2288 lines
126 KiB
HTML
2288 lines
126 KiB
HTML
<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge">
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<meta name="viewport" content="width=device-width, initial-scale=1">
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<meta name="description" content="Rules that flag suboptimal code.">
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<meta name="keywords" content=" Performance, AddEmptyString, AppendCharacterWithChar, AvoidArrayLoops, AvoidFileStream, AvoidInstantiatingObjectsInLoops, AvoidUsingShortType, BigIntegerInstantiation, BooleanInstantiation, ByteInstantiation, ConsecutiveAppendsShouldReuse, ConsecutiveLiteralAppends, InefficientEmptyStringCheck, InefficientStringBuffering, InsufficientStringBufferDeclaration, IntegerInstantiation, LongInstantiation, OptimizableToArrayCall, RedundantFieldInitializer, SimplifyStartsWith, ShortInstantiation, StringInstantiation, StringToString, TooFewBranchesForASwitchStatement, UnnecessaryWrapperObjectCreation, UseArrayListInsteadOfVector, UseArraysAsList, UseIndexOfChar, UselessStringValueOf, UseStringBufferForStringAppends, UseStringBufferLength">
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<title>Performance | PMD Source Code Analyzer</title>
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<link rel="stylesheet" href="css/syntax.css">
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<link rel="stylesheet" type="text/css" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css">
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<!--<link rel="stylesheet" type="text/css" href="css/bootstrap.min.css">-->
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<link rel="stylesheet" href="css/modern-business.css">
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<link rel="stylesheet" href="css/lavish-bootstrap.css">
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<link rel="stylesheet" href="css/customstyles.css">
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<link rel="stylesheet" href="css/theme-blue.css">
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<link rel="stylesheet" href="css/pmd-customstyles.css">
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<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script>
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<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery-cookie/1.4.1/jquery.cookie.min.js"></script>
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<script src="js/jquery.navgoco.min.js"></script>
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<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js"></script>
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<script src="https://cdnjs.cloudflare.com/ajax/libs/anchor-js/2.0.0/anchor.min.js"></script>
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<script src="js/toc.js"></script>
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<script src="js/customscripts.js"></script>
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<link rel="shortcut icon" href="images/favicon.ico" type="image/x-icon">
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<link rel="icon" href="images/favicon.ico" type="image/x-icon">
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<!-- HTML5 Shim and Respond.js IE8 support of HTML5 elements and media queries -->
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<!--[if lt IE 9]>
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<script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>
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<script src="https://oss.maxcdn.com/libs/respond.js/1.4.2/respond.min.js"></script>
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<![endif]-->
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<link rel="alternate" type="application/rss+xml" title="" href="https://pmd.github.io/pmd/feed.xml">
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<script>
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$(document).ready(function() {
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// Initialize navgoco with default options
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$("#mysidebar").navgoco({
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caretHtml: '',
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accordion: true,
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openClass: 'active', // open
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save: false, // leave false or nav highlighting doesn't work right
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cookie: {
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name: 'navgoco',
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expires: false,
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path: '/'
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},
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slide: {
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duration: 400,
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easing: 'swing'
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}
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});
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$("#collapseAll").click(function(e) {
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e.preventDefault();
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$("#mysidebar").navgoco('toggle', false);
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});
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$("#expandAll").click(function(e) {
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e.preventDefault();
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$("#mysidebar").navgoco('toggle', true);
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});
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});
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</script>
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<script>
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$(function () {
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$('[data-toggle="tooltip"]').tooltip()
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})
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</script>
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<script>
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$(document).ready(function() {
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$("#tg-sb-link").click(function() {
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$("#tg-sb-sidebar").toggle();
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$("#tg-sb-content").toggleClass('col-md-9');
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$("#tg-sb-content").toggleClass('col-md-12');
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$("#tg-sb-icon").toggleClass('fa-toggle-on');
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$("#tg-sb-icon").toggleClass('fa-toggle-off');
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});
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});
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</script>
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</head>
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<body>
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<!-- Content is offset by the height of the topnav bar. -->
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<!-- There's already a padding-top rule in modern-business.css, but it apparently doesn't work on Firefox 60 and Chrome 67 -->
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<div id="topbar-content-offset">
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<!-- Navigation -->
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<nav class="navbar navbar-inverse navbar-fixed-top">
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<div class="container topnavlinks">
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<div class="navbar-header">
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<button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
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<span class="sr-only">Toggle navigation</span>
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<span class="icon-bar"></span>
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<span class="icon-bar"></span>
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<span class="icon-bar"></span>
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</button>
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<a class="fa fa-home fa-lg navbar-brand" href="index.html"> <span class="projectTitle"> PMD Source Code Analyzer Project</span></a>
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</div>
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<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
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<ul class="nav navbar-nav navbar-right">
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<!-- toggle sidebar button -->
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<li><a id="tg-sb-link" href="#"><i id="tg-sb-icon" class="fa fa-toggle-on"></i> Nav</a></li>
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<!-- entries without drop-downs appear here -->
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<li><a href="https://github.com/pmd/pmd/releases/latest" target="_blank">Download</a></li>
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<li><a href="https://github.com/pmd/pmd" target="_blank">Fork us on github</a></li>
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<!-- entries with drop-downs appear here -->
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<!-- conditional logic to control which topnav appears for the audience defined in the configuration file.-->
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<!--comment out this block if you want to hide search-->
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<li>
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<!--start search-->
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<div id="search-demo-container">
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<input type="text" id="search-input" placeholder="search...">
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<ul id="results-container"></ul>
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</div>
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<script src="js/jekyll-search.js" type="text/javascript"></script>
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<script type="text/javascript">
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SimpleJekyllSearch.init({
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searchInput: document.getElementById('search-input'),
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resultsContainer: document.getElementById('results-container'),
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dataSource: 'search.json',
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searchResultTemplate: '<li><a href="{url}" title="Performance">{title}</a></li>',
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noResultsText: 'No results found.',
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limit: 10,
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fuzzy: true,
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})
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</script>
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<!--end search-->
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</li>
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</ul>
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</div>
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</div>
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<!-- /.container -->
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</nav>
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<!-- Page Content -->
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<div class="container">
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<div class="col-lg-12"> </div>
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<!-- Content Row -->
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<div class="row">
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<!-- Sidebar Column -->
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<div class="col-md-3" id="tg-sb-sidebar">
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<ul id="mysidebar" class="nav">
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<li class="sidebarTitle">PMD 6.10.0</li>
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<li>
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<a href="#">About</a>
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<ul>
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<li><a href="index.html">Home</a></li>
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<li><a href="pmd_release_notes.html">Release notes</a></li>
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<li><a href="pmd_about_help.html">Getting help</a></li>
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</ul>
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</li>
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<li>
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<a href="#">User Documentation</a>
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<ul>
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<li><a href="pmd_userdocs_installation.html">Installation and basic CLI usage</a></li>
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<li><a href="pmd_userdocs_making_rulesets.html">Making rulesets</a></li>
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<li><a href="pmd_userdocs_configuring_rules.html">Configuring rules</a></li>
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<li><a href="pmd_userdocs_best_practices.html">Best practices</a></li>
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<li><a href="pmd_userdocs_suppressing_warnings.html">Suppressing warnings</a></li>
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<li><a href="pmd_userdocs_incremental_analysis.html">Incremental analysis</a></li>
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||
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||
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||
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||
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||
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||
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||
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||
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||
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<li><a href="pmd_userdocs_cli_reference.html">PMD CLI reference</a></li>
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||
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||
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||
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||
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||
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||
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||
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||
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||
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||
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||
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||
<li class="subfolders">
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||
<a href="#">Extending PMD</a>
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||
<ul>
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||
|
||
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||
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||
<li><a href="pmd_userdocs_extending_writing_pmd_rules.html">Writing a rule</a></li>
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||
|
||
|
||
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||
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||
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||
<li><a href="pmd_userdocs_extending_writing_xpath_rules.html">Writing XPath rules</a></li>
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||
|
||
|
||
|
||
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||
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||
<li><a href="pmd_userdocs_extending_defining_properties.html">Defining rule properties</a></li>
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||
|
||
|
||
|
||
|
||
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||
<li><a href="pmd_userdocs_extending_metrics_howto.html">Using and defining code metrics</a></li>
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||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_userdocs_extending_rule_guidelines.html">Rule guidelines</a></li>
|
||
|
||
|
||
|
||
|
||
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||
<li><a href="pmd_userdocs_extending_testing.html">Testing your rules</a></li>
|
||
|
||
|
||
|
||
</ul>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_userdocs_cpd.html">Copy-paste detection</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
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||
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||
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||
<li class="subfolders">
|
||
<a href="#">Tools / Integrations</a>
|
||
<ul>
|
||
|
||
|
||
|
||
<li><a href="pmd_userdocs_tools_maven.html">Maven PMD plugin</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_userdocs_tools_ant.html">Ant</a></li>
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||
|
||
|
||
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||
|
||
|
||
<li><a href="pmd_userdocs_tools_ci.html">CI integrations</a></li>
|
||
|
||
|
||
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||
|
||
|
||
<li><a href="pmd_userdocs_tools.html">Other Tools / Integrations</a></li>
|
||
|
||
|
||
|
||
</ul>
|
||
</li>
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||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
</ul>
|
||
</li>
|
||
|
||
|
||
|
||
<li>
|
||
|
||
<a href="#">Rule Reference</a>
|
||
|
||
<ul>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="subfolders">
|
||
<a href="#">Apex Rules</a>
|
||
<ul>
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_apex.html">Index</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_apex_bestpractices.html">Best Practices</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_apex_codestyle.html">Code Style</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_apex_design.html">Design</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_apex_errorprone.html">Error Prone</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_apex_performance.html">Performance</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_apex_security.html">Security</a></li>
|
||
|
||
|
||
|
||
</ul>
|
||
</li>
|
||
|
||
|
||
|
||
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||
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||
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||
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||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="subfolders">
|
||
<a href="#">Ecmascript Rules</a>
|
||
<ul>
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_ecmascript.html">Index</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_ecmascript_bestpractices.html">Best Practices</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_ecmascript_codestyle.html">Code Style</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_ecmascript_errorprone.html">Error Prone</a></li>
|
||
|
||
|
||
|
||
</ul>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="subfolders">
|
||
<a href="#">Java Rules</a>
|
||
<ul>
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_java.html">Index</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_java_bestpractices.html">Best Practices</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_java_codestyle.html">Code Style</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_java_design.html">Design</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_java_documentation.html">Documentation</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_java_errorprone.html">Error Prone</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_java_multithreading.html">Multithreading</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li class="active"><a href="pmd_rules_java_performance.html">Performance</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_java_security.html">Security</a></li>
|
||
|
||
|
||
|
||
</ul>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="subfolders">
|
||
<a href="#">Java Server Pages Rules</a>
|
||
<ul>
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_jsp.html">Index</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_jsp_bestpractices.html">Best Practices</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_jsp_codestyle.html">Code Style</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_jsp_design.html">Design</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_jsp_errorprone.html">Error Prone</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_jsp_security.html">Security</a></li>
|
||
|
||
|
||
|
||
</ul>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="subfolders">
|
||
<a href="#">Maven POM Rules</a>
|
||
<ul>
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_pom.html">Index</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_pom_errorprone.html">Error Prone</a></li>
|
||
|
||
|
||
|
||
</ul>
|
||
</li>
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="subfolders">
|
||
<a href="#">PLSQL Rules</a>
|
||
<ul>
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_plsql.html">Index</a></li>
|
||
|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_plsql_bestpractices.html">Best Practices</a></li>
|
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|
||
|
||
|
||
|
||
|
||
<li><a href="pmd_rules_plsql_codestyle.html">Code Style</a></li>
|
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|
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|
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|
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|
||
|
||
|
||
|
||
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|
||
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|
||
|
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|
||
|
||
|
||
|
||
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||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="subfolders">
|
||
<a href="#">Salesforce VisualForce Rules</a>
|
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|
||
|
||
|
||
|
||
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|
||
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||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
|
||
<li class="subfolders">
|
||
<a href="#">VM Rules</a>
|
||
<ul>
|
||
|
||
|
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|
||
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|
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|
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|
||
|
||
|
||
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|
||
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|
||
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||
|
||
|
||
|
||
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|
||
|
||
|
||
|
||
|
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||
|
||
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|
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|
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|
||
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|
||
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|
||
|
||
|
||
|
||
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|
||
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|
||
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||
|
||
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||
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<li class="subfolders">
|
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||
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|
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|
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|
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<li>
|
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|
||
<a href="#">Language Specific Documentation</a>
|
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|
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|
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|
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|
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|
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|
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|
||
|
||
<li><a href="pmd_java_metrics_index.html">Java code metrics</a></li>
|
||
|
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|
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|
||
|
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|
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|
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|
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|
||
|
||
|
||
<li><a href="pmd_apex_metrics_index.html">Apex code metrics</a></li>
|
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|
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|
||
|
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||
|
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|
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|
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|
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||
|
||
<li><a href="pmd_devdocs_building.html">Building PMD from source</a></li>
|
||
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|
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|
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|
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|
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|
||
|
||
|
||
<li><a href="https://github.com/pmd/pmd/blob/master/CONTRIBUTING.md" target="_blank">Contributing</a></li>
|
||
|
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|
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|
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|
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|
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||
|
||
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|
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|
||
|
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<li><a href="pmd_devdocs_how_pmd_works.html">How PMD works</a></li>
|
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|
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|
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|
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|
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<li><a href="pmd_devdocs_pmdtester.html">Pmdtester</a></li>
|
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|
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||
|
||
|
||
|
||
|
||
|
||
<li class="subfolders">
|
||
<a href="#">Major contributions</a>
|
||
<ul>
|
||
|
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|
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|
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<li><a href="pmd_devdocs_major_adding_new_language.html">Adding a new language</a></li>
|
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|
||
|
||
|
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|
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|
||
<li><a href="pmd_devdocs_major_adding_new_cpd_language.html">Adding a new CPD language</a></li>
|
||
|
||
|
||
|
||
|
||
|
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<li><a href="pmd_devdocs_major_adding_new_metrics_framework.html">Adding metrics support to a language</a></li>
|
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|
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|
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</ul>
|
||
</li>
|
||
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<li>
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<a href="#">Project documentation</a>
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<ul>
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|
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|
||
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<li class="subfolders">
|
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<a href="#">Trivia about PMD</a>
|
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<ul>
|
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<li><a href="pmd_projectdocs_trivia_news.html">PMD in the press</a></li>
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<li><a href="pmd_projectdocs_trivia_products.html">Products & books related to PMD</a></li>
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<li><a href="pmd_projectdocs_trivia_similarprojects.html">Similar projects</a></li>
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|
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<li><a href="pmd_projectdocs_trivia_meaning.html">What does 'PMD' mean?</a></li>
|
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||
|
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<li><a href="pmd_projectdocs_credits.html">Credits</a></li>
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||
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||
|
||
<li><a href="pmd_release_notes_old.html">Old release notes</a></li>
|
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|
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<a href="#">Project management</a>
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<li><a href="pmd_projectdocs_committers_merging_pull_requests.html">Merging pull requests</a></li>
|
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|
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|
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<!-- Content Column -->
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<div class="col-md-9" id="tg-sb-content">
|
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<div class="post-header">
|
||
<h1 class="post-title-main">Performance</h1>
|
||
</div>
|
||
|
||
|
||
|
||
<div class="post-content">
|
||
|
||
|
||
<div class="summary">Rules that flag suboptimal code.</div>
|
||
|
||
|
||
|
||
|
||
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<div id="toc"></div>
|
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|
||
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||
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||
|
||
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||
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||
|
||
<a target="_blank" href="https://github.com/pmd/pmd/blob/master/docs/../pmd-java/src/main/resources/category/java/performance.xml" class="btn btn-default githubEditButton" role="button"><i class="fa fa-github fa-lg"></i> Edit me</a>
|
||
|
||
|
||
|
||
<h2 id="addemptystring">AddEmptyString</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 4.0</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>The conversion of literals to strings by concatenating them with empty strings is inefficient.
|
||
It is much better to use one of the type-specific toString() methods instead.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">AdditiveExpression</span><span class="o">/</span><span class="nt">PrimaryExpression</span><span class="o">/</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Literal</span><span class="p">[</span><span class="na">@Image</span><span class="err">=</span><span class="s1">'""'</span><span class="p">]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">String</span> <span class="n">s</span> <span class="o">=</span> <span class="s">""</span> <span class="o">+</span> <span class="mi">123</span><span class="o">;</span> <span class="c1">// inefficient</span>
|
||
<span class="n">String</span> <span class="n">t</span> <span class="o">=</span> <span class="n">Integer</span><span class="o">.</span><span class="na">toString</span><span class="o">(</span><span class="mi">456</span><span class="o">);</span> <span class="c1">// preferred approach</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/AddEmptyString"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="appendcharacterwithchar">AppendCharacterWithChar</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.5</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Avoid concatenating characters as strings in StringBuffer/StringBuilder.append methods.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/AppendCharacterWithCharRule.java">net.sourceforge.pmd.lang.java.rule.performance.AppendCharacterWithCharRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">StringBuffer</span> <span class="n">sb</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuffer</span><span class="o">();</span>
|
||
<span class="n">sb</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"a"</span><span class="o">);</span> <span class="c1">// avoid this</span>
|
||
|
||
<span class="n">StringBuffer</span> <span class="n">sb</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuffer</span><span class="o">();</span>
|
||
<span class="n">sb</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="sc">'a'</span><span class="o">);</span> <span class="c1">// use this instead</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/AppendCharacterWithChar"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="avoidarrayloops">AvoidArrayLoops</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.5</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Instead of manually copying data between two arrays, use the efficient Arrays.copyOf or System.arraycopy method instead.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">Statement</span><span class="p">[(</span><span class="nt">ForStatement</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="nt">WhileStatement</span><span class="p">)</span><span class="w"> </span><span class="ow">and</span><span class="w">
|
||
</span><span class="nf">count</span><span class="p">(</span><span class="err">*</span><span class="o">//</span><span class="nt">AssignmentOperator</span><span class="p">[</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="s1">'='</span><span class="p">])</span><span class="err">=</span><span class="m">1</span><span class="w">
|
||
</span><span class="ow">and</span><span class="w">
|
||
</span><span class="err">*</span><span class="o">/</span><span class="nt">Statement</span><span class="w">
|
||
</span><span class="p">[</span><span class="w">
|
||
</span><span class="p">.</span><span class="o">/</span><span class="nt">Block</span><span class="o">/</span><span class="nt">BlockStatement</span><span class="o">/</span><span class="nt">Statement</span><span class="o">/</span><span class="nt">StatementExpression</span><span class="o">/</span><span class="nt">PrimaryExpression</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="err">/</span><span class="p">..</span><span class="err">/</span><span class="p">..</span><span class="o">/</span><span class="nt">PrimarySuffix</span><span class="o">/</span><span class="nt">Expression</span><span class="w">
|
||
</span><span class="p">[(</span><span class="nt">PrimaryExpression</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="nt">AdditiveExpression</span><span class="p">)</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="nf">count</span><span class="w">
|
||
</span><span class="p">(.</span><span class="o">//</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="p">)</span><span class="err">=</span><span class="m">1</span><span class="p">]</span><span class="o">//</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="err">/</span><span class="na">@Image</span><span class="w">
|
||
</span><span class="ow">and</span><span class="w">
|
||
</span><span class="p">.</span><span class="o">/</span><span class="nt">Block</span><span class="o">/</span><span class="nt">BlockStatement</span><span class="o">/</span><span class="nt">Statement</span><span class="o">/</span><span class="nt">StatementExpression</span><span class="o">/</span><span class="nt">Expression</span><span class="o">/</span><span class="nt">PrimaryExpression</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="err">/</span><span class="p">..</span><span class="err">/</span><span class="p">..</span><span class="o">/</span><span class="nt">PrimarySuffix</span><span class="p">[</span><span class="nf">count</span><span class="w">
|
||
</span><span class="p">(..</span><span class="o">//</span><span class="nt">PrimarySuffix</span><span class="p">)</span><span class="err">=</span><span class="m">1</span><span class="p">]</span><span class="o">/</span><span class="nt">Expression</span><span class="p">[(</span><span class="nt">PrimaryExpression</span><span class="w">
|
||
</span><span class="ow">or</span><span class="w"> </span><span class="nt">AdditiveExpression</span><span class="p">)</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="nf">count</span><span class="p">(.</span><span class="o">//</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="p">)</span><span class="err">=</span><span class="m">1</span><span class="p">]</span><span class="w">
|
||
</span><span class="o">//</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="err">/</span><span class="na">@Image</span><span class="w">
|
||
</span><span class="p">]]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Test</span> <span class="o">{</span>
|
||
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">bar</span><span class="o">()</span> <span class="o">{</span>
|
||
<span class="kt">int</span><span class="o">[]</span> <span class="n">a</span> <span class="o">=</span> <span class="k">new</span> <span class="kt">int</span><span class="o">[</span><span class="mi">10</span><span class="o">];</span>
|
||
<span class="kt">int</span><span class="o">[]</span> <span class="n">b</span> <span class="o">=</span> <span class="k">new</span> <span class="kt">int</span><span class="o">[</span><span class="mi">10</span><span class="o">];</span>
|
||
<span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="o">;</span><span class="n">i</span><span class="o"><</span><span class="mi">10</span><span class="o">;</span><span class="n">i</span><span class="o">++)</span> <span class="o">{</span>
|
||
<span class="n">b</span><span class="o">[</span><span class="n">i</span><span class="o">]=</span><span class="n">a</span><span class="o">[</span><span class="n">i</span><span class="o">];</span>
|
||
<span class="o">}</span>
|
||
|
||
<span class="kt">int</span><span class="o">[]</span> <span class="n">c</span> <span class="o">=</span> <span class="k">new</span> <span class="kt">int</span><span class="o">[</span><span class="mi">10</span><span class="o">];</span>
|
||
<span class="c1">// this will trigger the rule</span>
|
||
<span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="o">;</span><span class="n">i</span><span class="o"><</span><span class="mi">10</span><span class="o">;</span><span class="n">i</span><span class="o">++)</span> <span class="o">{</span>
|
||
<span class="n">b</span><span class="o">[</span><span class="n">i</span><span class="o">]=</span><span class="n">a</span><span class="o">[</span><span class="n">c</span><span class="o">[</span><span class="n">i</span><span class="o">]];</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/AvoidArrayLoops"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="avoidfilestream">AvoidFileStream</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 6.0.0</p>
|
||
|
||
<p><strong>Priority:</strong> High (1)</p>
|
||
|
||
<p><strong>Minimum Language Version:</strong> Java 1.7</p>
|
||
|
||
<p>The FileInputStream and FileOutputStream classes contains a finalizer method which will cause garbage collection pauses. See <a href="https://bugs.openjdk.java.net/browse/JDK-8080225">JDK-8080225</a> for details.</p>
|
||
|
||
<p>The FileReader and FileWriter constructors instantiate FileInputStream and FileOutputStream, again causing garbage collection issues while finalizer methods are called.</p>
|
||
|
||
<ul>
|
||
<li>Use <code class="highlighter-rouge">Files.newInputStream(Paths.get(fileName))</code> instead of <code class="highlighter-rouge">new FileInputStream(fileName)</code>.</li>
|
||
<li>Use <code class="highlighter-rouge">Files.newOutputStream(Paths.get(fileName))</code> instead of <code class="highlighter-rouge">new FileOutputStream(fileName)</code>.</li>
|
||
<li>Use <code class="highlighter-rouge">Files.newBufferedReader(Paths.get(fileName))</code> instead of <code class="highlighter-rouge">new FileReader(fileName)</code>.</li>
|
||
<li>Use <code class="highlighter-rouge">Files.newBufferedWriter(Paths.get(fileName))</code> instead of <code class="highlighter-rouge">new FileWriter(fileName)</code>.</li>
|
||
</ul>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">AllocationExpression</span><span class="o">/</span><span class="nt">ClassOrInterfaceType</span><span class="p">[</span><span class="w">
|
||
</span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.io.FileInputStream'</span><span class="p">)</span><span class="w">
|
||
</span><span class="ow">or</span><span class="w"> </span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.io.FileOutputStream'</span><span class="p">)</span><span class="w">
|
||
</span><span class="ow">or</span><span class="w"> </span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.io.FileReader'</span><span class="p">)</span><span class="w">
|
||
</span><span class="ow">or</span><span class="w"> </span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.io.FileWriter'</span><span class="p">)</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// these instantiations cause garbage collection pauses, even if properly closed</span>
|
||
|
||
<span class="n">FileInputStream</span> <span class="n">fis</span> <span class="o">=</span> <span class="k">new</span> <span class="n">FileInputStream</span><span class="o">(</span><span class="n">fileName</span><span class="o">);</span>
|
||
<span class="n">FileOutputStream</span> <span class="n">fos</span> <span class="o">=</span> <span class="k">new</span> <span class="n">FileOutputStream</span><span class="o">(</span><span class="n">fileName</span><span class="o">);</span>
|
||
<span class="n">FileReader</span> <span class="n">fr</span> <span class="o">=</span> <span class="k">new</span> <span class="n">FileReader</span><span class="o">(</span><span class="n">fileName</span><span class="o">);</span>
|
||
<span class="n">FileWriter</span> <span class="n">fw</span> <span class="o">=</span> <span class="k">new</span> <span class="n">FileWriter</span><span class="o">(</span><span class="n">fileName</span><span class="o">);</span>
|
||
|
||
<span class="c1">// the following instantiations help prevent Garbage Collection pauses, no finalization</span>
|
||
|
||
<span class="k">try</span><span class="o">(</span><span class="n">InputStream</span> <span class="n">is</span> <span class="o">=</span> <span class="n">Files</span><span class="o">.</span><span class="na">newInputStream</span><span class="o">(</span><span class="n">Paths</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="n">fileName</span><span class="o">)))</span> <span class="o">{</span>
|
||
<span class="o">}</span>
|
||
<span class="k">try</span><span class="o">(</span><span class="n">OutputStream</span> <span class="n">os</span> <span class="o">=</span> <span class="n">Files</span><span class="o">.</span><span class="na">newOutputStream</span><span class="o">(</span><span class="n">Paths</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="n">fileName</span><span class="o">)))</span> <span class="o">{</span>
|
||
<span class="o">}</span>
|
||
<span class="k">try</span><span class="o">(</span><span class="n">BufferedReader</span> <span class="n">br</span> <span class="o">=</span> <span class="n">Files</span><span class="o">.</span><span class="na">newBufferedReader</span><span class="o">(</span><span class="n">Paths</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="n">fileName</span><span class="o">),</span> <span class="n">StandardCharsets</span><span class="o">.</span><span class="na">UTF_8</span><span class="o">))</span> <span class="o">{</span>
|
||
<span class="o">}</span>
|
||
<span class="k">try</span><span class="o">(</span><span class="n">BufferedWriter</span> <span class="n">wr</span> <span class="o">=</span> <span class="n">Files</span><span class="o">.</span><span class="na">newBufferedWriter</span><span class="o">(</span><span class="n">Paths</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="n">fileName</span><span class="o">),</span> <span class="n">StandardCharsets</span><span class="o">.</span><span class="na">UTF_8</span><span class="o">))</span> <span class="o">{</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/AvoidFileStream"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="avoidinstantiatingobjectsinloops">AvoidInstantiatingObjectsInLoops</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 2.2</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>New objects created within loops should be checked to see if they can created outside them and reused.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/AvoidInstantiatingObjectsInLoopsRule.java">net.sourceforge.pmd.lang.java.rule.performance.AvoidInstantiatingObjectsInLoopsRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Something</span> <span class="o">{</span>
|
||
<span class="kd">public</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">main</span><span class="o">(</span> <span class="n">String</span> <span class="n">as</span><span class="o">[]</span> <span class="o">)</span> <span class="o">{</span>
|
||
<span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o"><</span> <span class="mi">10</span><span class="o">;</span> <span class="n">i</span><span class="o">++)</span> <span class="o">{</span>
|
||
<span class="n">Foo</span> <span class="n">f</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Foo</span><span class="o">();</span> <span class="c1">// Avoid this whenever you can it's really expensive</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/AvoidInstantiatingObjectsInLoops"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="avoidusingshorttype">AvoidUsingShortType</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 4.1</p>
|
||
|
||
<p><strong>Priority:</strong> High (1)</p>
|
||
|
||
<p>Java uses the ‘short’ type to reduce memory usage, not to optimize calculation. In fact, the JVM does not have any
|
||
arithmetic capabilities for the short type: the JVM must convert the short into an int, do the proper calculation
|
||
and convert the int back to a short. Thus any storage gains found through use of the ‘short’ type may be offset by
|
||
adverse impacts on performance.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">FieldDeclaration</span><span class="o">/</span><span class="nt">Type</span><span class="o">/</span><span class="nt">PrimitiveType</span><span class="p">[</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="s1">'short'</span><span class="p">]</span><span class="w">
|
||
</span><span class="p">|</span><span class="w">
|
||
</span><span class="o">//</span><span class="nt">ClassOrInterfaceBodyDeclaration</span><span class="p">[</span><span class="ow">not</span><span class="p">(</span><span class="nt">Annotation</span><span class="o">/</span><span class="nt">MarkerAnnotation</span><span class="o">/</span><span class="nt">Name</span><span class="p">[</span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.lang.Override'</span><span class="p">)])]</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">MethodDeclaration</span><span class="o">/</span><span class="nt">ResultType</span><span class="o">/</span><span class="nt">Type</span><span class="o">/</span><span class="nt">PrimitiveType</span><span class="p">[</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="s1">'short'</span><span class="p">]</span><span class="w">
|
||
</span><span class="p">|</span><span class="w">
|
||
</span><span class="o">//</span><span class="nt">ClassOrInterfaceBodyDeclaration</span><span class="p">[</span><span class="ow">not</span><span class="p">(</span><span class="nt">Annotation</span><span class="o">/</span><span class="nt">MarkerAnnotation</span><span class="o">/</span><span class="nt">Name</span><span class="p">[</span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.lang.Override'</span><span class="p">)])]</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">MethodDeclaration</span><span class="o">/</span><span class="nt">MethodDeclarator</span><span class="o">/</span><span class="nt">FormalParameters</span><span class="o">/</span><span class="nt">FormalParameter</span><span class="o">/</span><span class="nt">Type</span><span class="o">/</span><span class="nt">PrimitiveType</span><span class="p">[</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="s1">'short'</span><span class="p">]</span><span class="w">
|
||
</span><span class="p">|</span><span class="w">
|
||
</span><span class="o">//</span><span class="nt">LocalVariableDeclaration</span><span class="o">/</span><span class="nt">Type</span><span class="o">/</span><span class="nt">PrimitiveType</span><span class="p">[</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="s1">'short'</span><span class="p">]</span><span class="w">
|
||
</span><span class="p">|</span><span class="w">
|
||
</span><span class="o">//</span><span class="nt">AnnotationMethodDeclaration</span><span class="o">/</span><span class="nt">Type</span><span class="o">/</span><span class="nt">PrimitiveType</span><span class="p">[</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="s1">'short'</span><span class="p">]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">UsingShort</span> <span class="o">{</span>
|
||
<span class="kd">private</span> <span class="kt">short</span> <span class="n">doNotUseShort</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
|
||
|
||
<span class="kd">public</span> <span class="nf">UsingShort</span><span class="o">()</span> <span class="o">{</span>
|
||
<span class="kt">short</span> <span class="n">shouldNotBeUsed</span> <span class="o">=</span> <span class="mi">1</span><span class="o">;</span>
|
||
<span class="n">doNotUseShort</span> <span class="o">+=</span> <span class="n">shouldNotBeUsed</span><span class="o">;</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/AvoidUsingShortType"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="bigintegerinstantiation">BigIntegerInstantiation</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.9</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Don’t create instances of already existing BigInteger (BigInteger.ZERO, BigInteger.ONE) and
|
||
for Java 1.5 onwards, BigInteger.TEN and BigDecimal (BigDecimal.ZERO, BigDecimal.ONE, BigDecimal.TEN)</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/BigIntegerInstantiationRule.java">net.sourceforge.pmd.lang.java.rule.performance.BigIntegerInstantiationRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">BigInteger</span> <span class="n">bi</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BigInteger</span><span class="o">(</span><span class="mi">1</span><span class="o">);</span> <span class="c1">// reference BigInteger.ONE instead</span>
|
||
<span class="n">BigInteger</span> <span class="n">bi2</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BigInteger</span><span class="o">(</span><span class="s">"0"</span><span class="o">);</span> <span class="c1">// reference BigInteger.ZERO instead</span>
|
||
<span class="n">BigInteger</span> <span class="n">bi3</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BigInteger</span><span class="o">(</span><span class="mf">0.0</span><span class="o">);</span> <span class="c1">// reference BigInteger.ZERO instead</span>
|
||
<span class="n">BigInteger</span> <span class="n">bi4</span><span class="o">;</span>
|
||
<span class="n">bi4</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BigInteger</span><span class="o">(</span><span class="mi">0</span><span class="o">);</span> <span class="c1">// reference BigInteger.ZERO instead</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/BigIntegerInstantiation"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="booleaninstantiation">BooleanInstantiation</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 1.2</p>
|
||
|
||
<p><strong>Priority:</strong> Medium High (2)</p>
|
||
|
||
<p>Avoid instantiating Boolean objects; you can reference Boolean.TRUE, Boolean.FALSE, or call Boolean.valueOf() instead.
|
||
Note that new Boolean() is deprecated since JDK 9 for that reason.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/BooleanInstantiationRule.java">net.sourceforge.pmd.lang.java.rule.performance.BooleanInstantiationRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">Boolean</span> <span class="n">bar</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Boolean</span><span class="o">(</span><span class="s">"true"</span><span class="o">);</span> <span class="c1">// unnecessary creation, just reference Boolean.TRUE;</span>
|
||
<span class="n">Boolean</span> <span class="n">buz</span> <span class="o">=</span> <span class="n">Boolean</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="kc">false</span><span class="o">);</span> <span class="c1">// ...., just reference Boolean.FALSE;</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/BooleanInstantiation"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="byteinstantiation">ByteInstantiation</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 4.0</p>
|
||
|
||
<p><strong>Priority:</strong> Medium High (2)</p>
|
||
|
||
<p>Calling new Byte() causes memory allocation that can be avoided by the static Byte.valueOf().
|
||
It makes use of an internal cache that recycles earlier instances making it more memory efficient.
|
||
Note that new Byte() is deprecated since JDK 9 for that reason.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">AllocationExpression</span><span class="w">
|
||
</span><span class="p">[</span><span class="ow">not</span><span class="w"> </span><span class="p">(</span><span class="nt">ArrayDimsAndInits</span><span class="p">)</span><span class="w">
|
||
</span><span class="ow">and</span><span class="w"> </span><span class="nt">ClassOrInterfaceType</span><span class="p">[</span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.lang.Byte'</span><span class="p">)]]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="o">{</span>
|
||
<span class="kd">private</span> <span class="n">Byte</span> <span class="n">i</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Byte</span><span class="o">(</span><span class="mi">0</span><span class="o">);</span> <span class="c1">// change to Byte i = Byte.valueOf(0);</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/ByteInstantiation"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="consecutiveappendsshouldreuse">ConsecutiveAppendsShouldReuse</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 5.1</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Consecutive calls to StringBuffer/StringBuilder .append should be chained, reusing the target object. This can improve the performance
|
||
by producing a smaller bytecode, reducing overhead and improving inlining. A complete analysis can be found <a href="https://github.com/pmd/pmd/issues/202#issuecomment-274349067">here</a></p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/ConsecutiveAppendsShouldReuseRule.java">net.sourceforge.pmd.lang.java.rule.performance.ConsecutiveAppendsShouldReuseRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">String</span> <span class="n">foo</span> <span class="o">=</span> <span class="s">" "</span><span class="o">;</span>
|
||
|
||
<span class="n">StringBuffer</span> <span class="n">buf</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuffer</span><span class="o">();</span>
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"Hello"</span><span class="o">);</span> <span class="c1">// poor</span>
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="n">foo</span><span class="o">);</span>
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"World"</span><span class="o">);</span>
|
||
|
||
<span class="n">StringBuffer</span> <span class="n">buf</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuffer</span><span class="o">();</span>
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"Hello"</span><span class="o">).</span><span class="na">append</span><span class="o">(</span><span class="n">foo</span><span class="o">).</span><span class="na">append</span><span class="o">(</span><span class="s">"World"</span><span class="o">);</span> <span class="c1">// good</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/ConsecutiveAppendsShouldReuse"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="consecutiveliteralappends">ConsecutiveLiteralAppends</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.5</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Consecutively calling StringBuffer/StringBuilder.append(…) with literals should be avoided.
|
||
Since the literals are constants, they can already be combined into a single String literal and this String
|
||
can be appended in a single method call.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/ConsecutiveLiteralAppendsRule.java">net.sourceforge.pmd.lang.java.rule.performance.ConsecutiveLiteralAppendsRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">StringBuilder</span> <span class="n">buf</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuilder</span><span class="o">();</span>
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"Hello"</span><span class="o">).</span><span class="na">append</span><span class="o">(</span><span class="s">" "</span><span class="o">).</span><span class="na">append</span><span class="o">(</span><span class="s">"World"</span><span class="o">);</span> <span class="c1">// poor</span>
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"Hello World"</span><span class="o">);</span> <span class="c1">// good</span>
|
||
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="sc">'h'</span><span class="o">).</span><span class="na">append</span><span class="o">(</span><span class="sc">'e'</span><span class="o">).</span><span class="na">append</span><span class="o">(</span><span class="sc">'l'</span><span class="o">).</span><span class="na">append</span><span class="o">(</span><span class="sc">'l'</span><span class="o">).</span><span class="na">append</span><span class="o">(</span><span class="sc">'o'</span><span class="o">);</span> <span class="c1">// poor</span>
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"hello"</span><span class="o">);</span> <span class="c1">// good</span>
|
||
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="mi">1</span><span class="o">).</span><span class="na">append</span><span class="o">(</span><span class="sc">'m'</span><span class="o">);</span> <span class="c1">// poor</span>
|
||
<span class="n">buf</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"1m"</span><span class="o">);</span> <span class="c1">// good</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>This rule has the following properties:</strong></p>
|
||
|
||
<table>
|
||
<thead>
|
||
<tr>
|
||
<th>Name</th>
|
||
<th>Default Value</th>
|
||
<th>Description</th>
|
||
<th>Multivalued</th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr>
|
||
<td>threshold</td>
|
||
<td>1</td>
|
||
<td>Max consecutive appends</td>
|
||
<td>no</td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/ConsecutiveLiteralAppends"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="inefficientemptystringcheck">InefficientEmptyStringCheck</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.6</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>String.trim().length() == 0 (or String.trim().isEmpty() for the same reason) is an inefficient
|
||
way to check if a String is really blank, as it creates a new String object just to check its size.
|
||
Consider creating a static function that loops through a string, checking Character.isWhitespace()
|
||
on each character and returning false if a non-whitespace character is found. A Smarter code to
|
||
check for an empty string would be:</p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">private</span> <span class="kt">boolean</span> <span class="nf">checkTrimEmpty</span><span class="o">(</span><span class="n">String</span> <span class="n">str</span><span class="o">)</span> <span class="o">{</span>
|
||
<span class="k">for</span><span class="o">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">str</span><span class="o">.</span><span class="na">length</span><span class="o">();</span> <span class="n">i</span><span class="o">++)</span> <span class="o">{</span>
|
||
<span class="k">if</span><span class="o">(!</span><span class="n">Character</span><span class="o">.</span><span class="na">isWhitespace</span><span class="o">(</span><span class="n">str</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="n">i</span><span class="o">)))</span> <span class="o">{</span>
|
||
<span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
<span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p>You can refer to Apache’s StringUtils#isBlank (in commons-lang),
|
||
Spring’s StringUtils#hasText (in the Spring framework) or Google’s
|
||
CharMatcher#whitespace (in Guava) for existing implementations (some might
|
||
include the check for != null).</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/InefficientEmptyStringCheckRule.java">net.sourceforge.pmd.lang.java.rule.performance.InefficientEmptyStringCheckRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kt">void</span> <span class="nf">bar</span><span class="o">(</span><span class="n">String</span> <span class="n">string</span><span class="o">)</span> <span class="o">{</span>
|
||
<span class="k">if</span> <span class="o">(</span><span class="n">string</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">&&</span> <span class="n">string</span><span class="o">.</span><span class="na">trim</span><span class="o">().</span><span class="na">length</span><span class="o">()</span> <span class="o">></span> <span class="mi">0</span><span class="o">)</span> <span class="o">{</span>
|
||
<span class="n">doSomething</span><span class="o">();</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/InefficientEmptyStringCheck"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="inefficientstringbuffering">InefficientStringBuffering</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.4</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Avoid concatenating non-literals in a StringBuffer constructor or append() since intermediate buffers will
|
||
need to be be created and destroyed by the JVM.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/InefficientStringBufferingRule.java">net.sourceforge.pmd.lang.java.rule.performance.InefficientStringBufferingRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// Avoid this, two buffers are actually being created here</span>
|
||
<span class="n">StringBuffer</span> <span class="n">sb</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuffer</span><span class="o">(</span><span class="s">"tmp = "</span><span class="o">+</span><span class="n">System</span><span class="o">.</span><span class="na">getProperty</span><span class="o">(</span><span class="s">"java.io.tmpdir"</span><span class="o">));</span>
|
||
|
||
<span class="c1">// do this instead</span>
|
||
<span class="n">StringBuffer</span> <span class="n">sb</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuffer</span><span class="o">(</span><span class="s">"tmp = "</span><span class="o">);</span>
|
||
<span class="n">sb</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="n">System</span><span class="o">.</span><span class="na">getProperty</span><span class="o">(</span><span class="s">"java.io.tmpdir"</span><span class="o">));</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/InefficientStringBuffering"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="insufficientstringbufferdeclaration">InsufficientStringBufferDeclaration</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.6</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Failing to pre-size a StringBuffer or StringBuilder properly could cause it to re-size many times
|
||
during runtime. This rule attempts to determine the total number the characters that are actually
|
||
passed into StringBuffer.append(), but represents a best guess “worst case” scenario. An empty
|
||
StringBuffer/StringBuilder constructor initializes the object to 16 characters. This default
|
||
is assumed if the length of the constructor can not be determined.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/InsufficientStringBufferDeclarationRule.java">net.sourceforge.pmd.lang.java.rule.performance.InsufficientStringBufferDeclarationRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">StringBuffer</span> <span class="n">bad</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuffer</span><span class="o">();</span>
|
||
<span class="n">bad</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"This is a long string that will exceed the default 16 characters"</span><span class="o">);</span>
|
||
|
||
<span class="n">StringBuffer</span> <span class="n">good</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuffer</span><span class="o">(</span><span class="mi">41</span><span class="o">);</span>
|
||
<span class="n">good</span><span class="o">.</span><span class="na">append</span><span class="o">(</span><span class="s">"This is a long string, which is pre-sized"</span><span class="o">);</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/InsufficientStringBufferDeclaration"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="integerinstantiation">IntegerInstantiation</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.5</p>
|
||
|
||
<p><strong>Priority:</strong> Medium High (2)</p>
|
||
|
||
<p>Calling new Integer() causes memory allocation that can be avoided by the static Integer.valueOf().
|
||
It makes use of an internal cache that recycles earlier instances making it more memory efficient.
|
||
Note that new Integer() is deprecated since JDK 9 for that reason.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">AllocationExpression</span><span class="w">
|
||
</span><span class="p">[</span><span class="ow">not</span><span class="w"> </span><span class="p">(</span><span class="nt">ArrayDimsAndInits</span><span class="p">)</span><span class="w">
|
||
</span><span class="ow">and</span><span class="w"> </span><span class="nt">ClassOrInterfaceType</span><span class="p">[</span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.lang.Integer'</span><span class="p">)]]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="o">{</span>
|
||
<span class="kd">private</span> <span class="n">Integer</span> <span class="n">i</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Integer</span><span class="o">(</span><span class="mi">0</span><span class="o">);</span> <span class="c1">// change to Integer i = Integer.valueOf(0);</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/IntegerInstantiation"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="longinstantiation">LongInstantiation</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 4.0</p>
|
||
|
||
<p><strong>Priority:</strong> Medium High (2)</p>
|
||
|
||
<p>Calling new Long() causes memory allocation that can be avoided by the static Long.valueOf().
|
||
It makes use of an internal cache that recycles earlier instances making it more memory efficient.
|
||
Note that new Long() is deprecated since JDK 9 for that reason.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">AllocationExpression</span><span class="w">
|
||
</span><span class="p">[</span><span class="ow">not</span><span class="w"> </span><span class="p">(</span><span class="nt">ArrayDimsAndInits</span><span class="p">)</span><span class="w">
|
||
</span><span class="ow">and</span><span class="w"> </span><span class="nt">ClassOrInterfaceType</span><span class="p">[</span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.lang.Long'</span><span class="p">)]]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="o">{</span>
|
||
<span class="kd">private</span> <span class="n">Long</span> <span class="n">i</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Long</span><span class="o">(</span><span class="mi">0</span><span class="o">);</span> <span class="c1">// change to Long i = Long.valueOf(0);</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/LongInstantiation"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="optimizabletoarraycall">OptimizableToArrayCall</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 1.8</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p><strong>Minimum Language Version:</strong> Java 1.6</p>
|
||
|
||
<p>Calls to a collection’s <code class="highlighter-rouge">toArray(E[])</code> method should specify a target array of zero size. This allows the JVM
|
||
to optimize the memory allocation and copying as much as possible.</p>
|
||
|
||
<p>Previous versions of this rule (pre PMD 6.0.0) suggested the opposite, but current JVM implementations
|
||
perform always better, when they have full control over the target array. And allocation an array via
|
||
reflection is nowadays as fast as the direct allocation.</p>
|
||
|
||
<p>See also <a href="https://shipilev.net/blog/2016/arrays-wisdom-ancients/">Arrays of Wisdom of the Ancients</a></p>
|
||
|
||
<p>Note: If you don’t need an array of the correct type, then the simple <code class="highlighter-rouge">toArray()</code> method without an array
|
||
is faster, but returns only an array of type <code class="highlighter-rouge">Object[]</code>.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">PrimaryExpression</span><span class="w">
|
||
</span><span class="p">[</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="p">[</span><span class="nf">ends-with</span><span class="p">(</span><span class="na">@Image</span><span class="p">,</span><span class="w"> </span><span class="s1">'toArray'</span><span class="p">)]]</span><span class="w">
|
||
</span><span class="p">[</span><span class="w">
|
||
</span><span class="nt">PrimarySuffix</span><span class="o">/</span><span class="nt">Arguments</span><span class="o">/</span><span class="nt">ArgumentList</span><span class="o">/</span><span class="nt">Expression</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">PrimaryExpression</span><span class="o">/</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">AllocationExpression</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">ArrayDimsAndInits</span><span class="o">/</span><span class="nt">Expression</span><span class="o">/</span><span class="nt">PrimaryExpression</span><span class="o">/</span><span class="nt">PrimaryPrefix</span><span class="p">[</span><span class="ow">not</span><span class="p">(</span><span class="nt">Literal</span><span class="p">[</span><span class="na">@Image</span><span class="err">=</span><span class="s1">'0'</span><span class="p">])]</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">List</span><span class="o"><</span><span class="n">Foo</span><span class="o">></span> <span class="n">foos</span> <span class="o">=</span> <span class="n">getFoos</span><span class="o">();</span>
|
||
|
||
<span class="c1">// much better; this one allows the jvm to allocate an array of the correct size and effectively skip</span>
|
||
<span class="c1">// the zeroing, since each array element will be overridden anyways</span>
|
||
<span class="n">Foo</span><span class="o">[]</span> <span class="n">fooArray</span> <span class="o">=</span> <span class="n">foos</span><span class="o">.</span><span class="na">toArray</span><span class="o">(</span><span class="k">new</span> <span class="n">Foo</span><span class="o">[</span><span class="mi">0</span><span class="o">]);</span>
|
||
|
||
<span class="c1">// inefficient, the array needs to be zeroed out by the jvm before it is handed over to the toArray method</span>
|
||
<span class="n">Foo</span><span class="o">[]</span> <span class="n">fooArray</span> <span class="o">=</span> <span class="n">foos</span><span class="o">.</span><span class="na">toArray</span><span class="o">(</span><span class="k">new</span> <span class="n">Foo</span><span class="o">[</span><span class="n">foos</span><span class="o">.</span><span class="na">size</span><span class="o">()]);</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/OptimizableToArrayCall"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="redundantfieldinitializer">RedundantFieldInitializer</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 5.0</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Java will initialize fields with known default values so any explicit initialization of those same defaults
|
||
is redundant and results in a larger class file (approximately three additional bytecode instructions per field).</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/RedundantFieldInitializerRule.java">net.sourceforge.pmd.lang.java.rule.performance.RedundantFieldInitializerRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">C</span> <span class="o">{</span>
|
||
<span class="kt">boolean</span> <span class="n">b</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span> <span class="c1">// examples of redundant initializers</span>
|
||
<span class="kt">byte</span> <span class="n">by</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
|
||
<span class="kt">short</span> <span class="n">s</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
|
||
<span class="kt">char</span> <span class="n">c</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
|
||
<span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
|
||
<span class="kt">long</span> <span class="n">l</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
|
||
|
||
<span class="kt">float</span> <span class="n">f</span> <span class="o">=</span> <span class="o">.</span><span class="mi">0</span><span class="n">f</span><span class="o">;</span> <span class="c1">// all possible float literals</span>
|
||
<span class="n">doable</span> <span class="n">d</span> <span class="o">=</span> <span class="mi">0</span><span class="n">d</span><span class="o">;</span> <span class="c1">// all possible double literals</span>
|
||
<span class="n">Object</span> <span class="n">o</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
|
||
|
||
<span class="n">MyClass</span> <span class="n">mca</span><span class="o">[]</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
|
||
<span class="kt">int</span> <span class="n">i1</span> <span class="o">=</span> <span class="mi">0</span><span class="o">,</span> <span class="n">ia1</span><span class="o">[]</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
|
||
|
||
<span class="kd">class</span> <span class="nc">Nested</span> <span class="o">{</span>
|
||
<span class="kt">boolean</span> <span class="n">b</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/RedundantFieldInitializer"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="shortinstantiation">ShortInstantiation</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 4.0</p>
|
||
|
||
<p><strong>Priority:</strong> Medium High (2)</p>
|
||
|
||
<p>Calling new Short() causes memory allocation that can be avoided by the static Short.valueOf().
|
||
It makes use of an internal cache that recycles earlier instances making it more memory efficient.
|
||
Note that new Short() is deprecated since JDK 9 for that reason.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">AllocationExpression</span><span class="w">
|
||
</span><span class="p">[</span><span class="ow">not</span><span class="w"> </span><span class="p">(</span><span class="nt">ArrayDimsAndInits</span><span class="p">)</span><span class="w">
|
||
</span><span class="ow">and</span><span class="w"> </span><span class="nt">ClassOrInterfaceType</span><span class="p">[</span><span class="nn">pmd-java:</span><span class="nf">typeIs</span><span class="p">(</span><span class="s1">'java.lang.Short'</span><span class="p">)]]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="o">{</span>
|
||
<span class="kd">private</span> <span class="n">Short</span> <span class="n">i</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Short</span><span class="o">(</span><span class="mi">0</span><span class="o">);</span> <span class="c1">// change to Short i = Short.valueOf(0);</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/ShortInstantiation"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="simplifystartswith">SimplifyStartsWith</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.1</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Since it passes in a literal of length 1, calls to (string).startsWith can be rewritten using (string).charAt(0)
|
||
at the expense of some readability.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">PrimaryExpression</span><span class="w">
|
||
</span><span class="p">[</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="w">
|
||
</span><span class="p">[</span><span class="nf">ends-with</span><span class="p">(</span><span class="na">@Image</span><span class="p">,</span><span class="w"> </span><span class="s1">'.startsWith'</span><span class="p">)]</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="nt">PrimarySuffix</span><span class="p">[</span><span class="na">@Image</span><span class="err">=</span><span class="s1">'startsWith'</span><span class="p">]]</span><span class="w">
|
||
</span><span class="p">[</span><span class="nt">PrimarySuffix</span><span class="o">/</span><span class="nt">Arguments</span><span class="o">/</span><span class="nt">ArgumentList</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">Expression</span><span class="o">/</span><span class="nt">PrimaryExpression</span><span class="o">/</span><span class="nt">PrimaryPrefix</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">Literal</span><span class="w">
|
||
</span><span class="p">[</span><span class="nf">string-length</span><span class="p">(</span><span class="na">@Image</span><span class="p">)</span><span class="err">=</span><span class="m">3</span><span class="p">]</span><span class="w">
|
||
</span><span class="p">[</span><span class="nf">starts-with</span><span class="p">(</span><span class="na">@Image</span><span class="p">,</span><span class="w"> </span><span class="s1">'"'</span><span class="p">)]</span><span class="w">
|
||
</span><span class="p">[</span><span class="nf">ends-with</span><span class="p">(</span><span class="na">@Image</span><span class="p">,</span><span class="w"> </span><span class="s1">'"'</span><span class="p">)]</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="o">{</span>
|
||
|
||
<span class="kt">boolean</span> <span class="nf">checkIt</span><span class="o">(</span><span class="n">String</span> <span class="n">x</span><span class="o">)</span> <span class="o">{</span>
|
||
<span class="k">return</span> <span class="n">x</span><span class="o">.</span><span class="na">startsWith</span><span class="o">(</span><span class="s">"a"</span><span class="o">);</span> <span class="c1">// suboptimal</span>
|
||
<span class="o">}</span>
|
||
|
||
<span class="kt">boolean</span> <span class="nf">fasterCheckIt</span><span class="o">(</span><span class="n">String</span> <span class="n">x</span><span class="o">)</span> <span class="o">{</span>
|
||
<span class="k">return</span> <span class="n">x</span><span class="o">.</span><span class="na">charAt</span><span class="o">(</span><span class="mi">0</span><span class="o">)</span> <span class="o">==</span> <span class="sc">'a'</span><span class="o">;</span> <span class="c1">// faster approach</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/SimplifyStartsWith"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="stringinstantiation">StringInstantiation</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 1.0</p>
|
||
|
||
<p><strong>Priority:</strong> Medium High (2)</p>
|
||
|
||
<p>Avoid instantiating String objects; this is usually unnecessary since they are immutable and can be safely shared.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/StringInstantiationRule.java">net.sourceforge.pmd.lang.java.rule.performance.StringInstantiationRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">private</span> <span class="n">String</span> <span class="n">bar</span> <span class="o">=</span> <span class="k">new</span> <span class="n">String</span><span class="o">(</span><span class="s">"bar"</span><span class="o">);</span> <span class="c1">// just do a String bar = "bar";</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/StringInstantiation"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="stringtostring">StringToString</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 1.0</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Avoid calling toString() on objects already known to be string instances; this is unnecessary.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/StringToStringRule.java">net.sourceforge.pmd.lang.java.rule.performance.StringToStringRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">private</span> <span class="n">String</span> <span class="nf">baz</span><span class="o">()</span> <span class="o">{</span>
|
||
<span class="n">String</span> <span class="n">bar</span> <span class="o">=</span> <span class="s">"howdy"</span><span class="o">;</span>
|
||
<span class="k">return</span> <span class="n">bar</span><span class="o">.</span><span class="na">toString</span><span class="o">();</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/StringToString"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="toofewbranchesforaswitchstatement">TooFewBranchesForASwitchStatement</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 4.2</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Switch statements are intended to be used to support complex branching behaviour. Using a switch for only a few
|
||
cases is ill-advised, since switches are not as easy to understand as if-then statements. In these cases use the
|
||
if-then statement to increase code readability.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">SwitchStatement</span><span class="p">[</span><span class="w">
|
||
</span><span class="p">(</span><span class="nf">count</span><span class="p">(.</span><span class="o">//</span><span class="nt">SwitchLabel</span><span class="p">)</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="nv">$minimumNumberCaseForASwitch</span><span class="p">)</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// With a minimumNumberCaseForASwitch of 3</span>
|
||
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="o">{</span>
|
||
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">bar</span><span class="o">()</span> <span class="o">{</span>
|
||
<span class="k">switch</span> <span class="o">(</span><span class="n">condition</span><span class="o">)</span> <span class="o">{</span>
|
||
<span class="k">case</span> <span class="nl">ONE:</span>
|
||
<span class="n">instruction</span><span class="o">;</span>
|
||
<span class="k">break</span><span class="o">;</span>
|
||
<span class="k">default</span><span class="o">:</span>
|
||
<span class="k">break</span><span class="o">;</span> <span class="c1">// not enough for a 'switch' stmt, a simple 'if' stmt would have been more appropriate</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>This rule has the following properties:</strong></p>
|
||
|
||
<table>
|
||
<thead>
|
||
<tr>
|
||
<th>Name</th>
|
||
<th>Default Value</th>
|
||
<th>Description</th>
|
||
<th>Multivalued</th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr>
|
||
<td>minimumNumberCaseForASwitch</td>
|
||
<td>3</td>
|
||
<td>Minimum number of branches for a switch</td>
|
||
<td>no</td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/TooFewBranchesForASwitchStatement"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="unnecessarywrapperobjectcreation">UnnecessaryWrapperObjectCreation</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.8</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Most wrapper classes provide static conversion methods that avoid the need to create intermediate objects
|
||
just to create the primitive forms. Using these avoids the cost of creating objects that also need to be
|
||
garbage-collected later.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/UnnecessaryWrapperObjectCreationRule.java">net.sourceforge.pmd.lang.java.rule.performance.UnnecessaryWrapperObjectCreationRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kt">int</span> <span class="nf">convert</span><span class="o">(</span><span class="n">String</span> <span class="n">s</span><span class="o">)</span> <span class="o">{</span>
|
||
<span class="kt">int</span> <span class="n">i</span><span class="o">,</span> <span class="n">i2</span><span class="o">;</span>
|
||
|
||
<span class="n">i</span> <span class="o">=</span> <span class="n">Integer</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="n">s</span><span class="o">).</span><span class="na">intValue</span><span class="o">();</span> <span class="c1">// this wastes an object</span>
|
||
<span class="n">i</span> <span class="o">=</span> <span class="n">Integer</span><span class="o">.</span><span class="na">parseInt</span><span class="o">(</span><span class="n">s</span><span class="o">);</span> <span class="c1">// this is better</span>
|
||
|
||
<span class="n">i2</span> <span class="o">=</span> <span class="n">Integer</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="n">i</span><span class="o">).</span><span class="na">intValue</span><span class="o">();</span> <span class="c1">// this wastes an object</span>
|
||
<span class="n">i2</span> <span class="o">=</span> <span class="n">i</span><span class="o">;</span> <span class="c1">// this is better</span>
|
||
|
||
<span class="n">String</span> <span class="n">s3</span> <span class="o">=</span> <span class="n">Integer</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="n">i2</span><span class="o">).</span><span class="na">toString</span><span class="o">();</span> <span class="c1">// this wastes an object</span>
|
||
<span class="n">s3</span> <span class="o">=</span> <span class="n">Integer</span><span class="o">.</span><span class="na">toString</span><span class="o">(</span><span class="n">i2</span><span class="o">);</span> <span class="c1">// this is better</span>
|
||
|
||
<span class="k">return</span> <span class="n">i2</span><span class="o">;</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/UnnecessaryWrapperObjectCreation"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="usearraylistinsteadofvector">UseArrayListInsteadOfVector</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.0</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>ArrayList is a much better Collection implementation than Vector if thread-safe operation is not required.</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">CompilationUnit</span><span class="p">[</span><span class="nf">count</span><span class="p">(</span><span class="nt">ImportDeclaration</span><span class="p">)</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="m">0</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="nf">count</span><span class="p">(</span><span class="nt">ImportDeclaration</span><span class="o">/</span><span class="nt">Name</span><span class="p">[</span><span class="na">@Image</span><span class="err">=</span><span class="s1">'java.util.Vector'</span><span class="p">])</span><span class="w"> </span><span class="o">></span><span class="w"> </span><span class="m">0</span><span class="p">]</span><span class="w">
|
||
</span><span class="o">//</span><span class="nt">AllocationExpression</span><span class="o">/</span><span class="nt">ClassOrInterfaceType</span><span class="w">
|
||
</span><span class="p">[</span><span class="na">@Image</span><span class="err">=</span><span class="s1">'Vector'</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="na">@Image</span><span class="err">=</span><span class="s1">'java.util.Vector'</span><span class="p">]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">SimpleTest</span> <span class="kd">extends</span> <span class="n">TestCase</span> <span class="o">{</span>
|
||
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">testX</span><span class="o">()</span> <span class="o">{</span>
|
||
<span class="n">Collection</span> <span class="n">c1</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Vector</span><span class="o">();</span>
|
||
<span class="n">Collection</span> <span class="n">c2</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o">();</span> <span class="c1">// achieves the same with much better performance</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/UseArrayListInsteadOfVector"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="usearraysaslist">UseArraysAsList</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.5</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>The java.util.Arrays class has a “asList” method that should be used when you want to create a new List from
|
||
an array of objects. It is faster than executing a loop to copy all the elements of the array one by one.</p>
|
||
|
||
<p>Note that the result of Arrays.asList() is backed by the specified array,
|
||
changes in the returned list will result in the array to be modified.
|
||
For that reason, it is not possible to add new elements to the returned list of Arrays.asList() (UnsupportedOperationException).
|
||
You must use new ArrayList<>(Arrays.asList(…)) if that is inconvenient for you (e.g. because of concurrent access).</p>
|
||
|
||
<p><strong>This rule is defined by the following XPath expression:</strong></p>
|
||
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">Statement</span><span class="p">[</span><span class="w">
|
||
</span><span class="p">(</span><span class="nt">ForStatement</span><span class="p">)</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="p">(</span><span class="nt">ForStatement</span><span class="o">//</span><span class="nt">VariableInitializer</span><span class="o">//</span><span class="nt">Literal</span><span class="p">[</span><span class="na">@IntLiteral</span><span class="err">=</span><span class="s1">'true'</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="na">@Image</span><span class="err">=</span><span class="s1">'0'</span><span class="p">])</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="p">(</span><span class="nf">count</span><span class="p">(.</span><span class="o">//</span><span class="nt">IfStatement</span><span class="p">)</span><span class="err">=</span><span class="m">0</span><span class="p">)</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span><span class="o">//</span><span class="nt">StatementExpression</span><span class="p">[</span><span class="w">
|
||
</span><span class="nt">PrimaryExpression</span><span class="o">/</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="p">[</span><span class="w">
|
||
</span><span class="nf">substring-before</span><span class="p">(</span><span class="na">@Image</span><span class="p">,</span><span class="s1">'.add'</span><span class="p">)</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="kn">ancestor::</span><span class="nt">MethodDeclaration</span><span class="o">//</span><span class="nt">LocalVariableDeclaration</span><span class="p">[</span><span class="w">
|
||
</span><span class="p">.</span><span class="o">/</span><span class="nt">Type</span><span class="o">//</span><span class="nt">ClassOrInterfaceType</span><span class="p">[</span><span class="w">
|
||
</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="s1">'Collection'</span><span class="w"> </span><span class="ow">or</span><span class="w">
|
||
</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="s1">'List'</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="na">@Image</span><span class="err">=</span><span class="s1">'ArrayList'</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">VariableDeclarator</span><span class="o">/</span><span class="nt">VariableDeclaratorId</span><span class="p">[</span><span class="w">
|
||
</span><span class="nf">count</span><span class="p">(..</span><span class="o">//</span><span class="nt">AllocationExpression</span><span class="o">/</span><span class="nt">ClassOrInterfaceType</span><span class="p">[</span><span class="w">
|
||
</span><span class="na">@Image</span><span class="err">=</span><span class="s2">"ArrayList"</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span><span class="p">)</span><span class="err">=</span><span class="m">1</span><span class="w">
|
||
</span><span class="p">]</span><span class="err">/</span><span class="na">@Image</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span><span class="ow">and</span><span class="w">
|
||
</span><span class="nt">PrimaryExpression</span><span class="o">/</span><span class="nt">PrimarySuffix</span><span class="o">/</span><span class="nt">Arguments</span><span class="o">/</span><span class="nt">ArgumentList</span><span class="o">/</span><span class="nt">Expression</span><span class="o">/</span><span class="nt">PrimaryExpression</span><span class="o">/</span><span class="nt">PrimaryPrefix</span><span class="o">/</span><span class="nt">Name</span><span class="w">
|
||
</span><span class="p">[</span><span class="w">
|
||
</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="kn">ancestor::</span><span class="nt">MethodDeclaration</span><span class="o">//</span><span class="nt">LocalVariableDeclaration</span><span class="p">[</span><span class="na">@Array</span><span class="err">=</span><span class="s2">"true"</span><span class="p">]</span><span class="o">/</span><span class="nt">VariableDeclarator</span><span class="o">/</span><span class="nt">VariableDeclaratorId</span><span class="err">/</span><span class="na">@Image</span><span class="w">
|
||
</span><span class="ow">or</span><span class="w">
|
||
</span><span class="na">@Image</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="kn">ancestor::</span><span class="nt">MethodDeclaration</span><span class="o">//</span><span class="nt">FormalParameter</span><span class="o">/</span><span class="nt">VariableDeclaratorId</span><span class="err">/</span><span class="na">@Image</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span><span class="err">/</span><span class="p">..</span><span class="err">/</span><span class="p">..[</span><span class="nf">count</span><span class="p">(.</span><span class="o">//</span><span class="nt">PrimarySuffix</span><span class="p">)</span><span class="w">
|
||
</span><span class="err">=</span><span class="m">1</span><span class="p">]</span><span class="o">/</span><span class="nt">PrimarySuffix</span><span class="o">/</span><span class="nt">Expression</span><span class="o">/</span><span class="nt">PrimaryExpression</span><span class="o">/</span><span class="nt">PrimaryPrefix</span><span class="w">
|
||
</span><span class="o">/</span><span class="nt">Name</span><span class="w">
|
||
</span><span class="p">]</span><span class="w">
|
||
</span></code></pre></div></div>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Test</span> <span class="o">{</span>
|
||
<span class="kd">public</span> <span class="kt">void</span> <span class="nf">foo</span><span class="o">(</span><span class="n">Integer</span><span class="o">[]</span> <span class="n">ints</span><span class="o">)</span> <span class="o">{</span>
|
||
<span class="c1">// could just use Arrays.asList(ints)</span>
|
||
<span class="n">List</span><span class="o"><</span><span class="n">Integer</span><span class="o">></span> <span class="n">l</span><span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o"><>(</span><span class="mi">100</span><span class="o">);</span>
|
||
<span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="o">;</span> <span class="n">i</span><span class="o"><</span> <span class="mi">100</span><span class="o">;</span> <span class="n">i</span><span class="o">++)</span> <span class="o">{</span>
|
||
<span class="n">l</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="n">ints</span><span class="o">[</span><span class="n">i</span><span class="o">]);</span>
|
||
<span class="o">}</span>
|
||
<span class="k">for</span> <span class="o">(</span><span class="kt">int</span> <span class="n">i</span><span class="o">=</span><span class="mi">0</span><span class="o">;</span> <span class="n">i</span><span class="o"><</span> <span class="mi">100</span><span class="o">;</span> <span class="n">i</span><span class="o">++)</span> <span class="o">{</span>
|
||
<span class="n">l</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="n">a</span><span class="o">[</span><span class="n">i</span><span class="o">].</span><span class="na">toString</span><span class="o">());</span> <span class="c1">// won't trigger the rule</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/UseArraysAsList"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="useindexofchar">UseIndexOfChar</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.5</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Use String.indexOf(char) when checking for the index of a single character; it executes faster.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/UseIndexOfCharRule.java">net.sourceforge.pmd.lang.java.rule.performance.UseIndexOfCharRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">String</span> <span class="n">s</span> <span class="o">=</span> <span class="s">"hello world"</span><span class="o">;</span>
|
||
<span class="c1">// avoid this</span>
|
||
<span class="k">if</span> <span class="o">(</span><span class="n">s</span><span class="o">.</span><span class="na">indexOf</span><span class="o">(</span><span class="s">"d"</span><span class="o">)</span> <span class="o">{}</span>
|
||
<span class="c1">// instead do this</span>
|
||
<span class="k">if</span> <span class="o">(</span><span class="n">s</span><span class="o">.</span><span class="na">indexOf</span><span class="o">(</span><span class="sc">'d'</span><span class="o">)</span> <span class="o">{}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/UseIndexOfChar"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="uselessstringvalueof">UselessStringValueOf</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.8</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>No need to call String.valueOf to append to a string; just use the valueOf() argument directly.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/UselessStringValueOfRule.java">net.sourceforge.pmd.lang.java.rule.performance.UselessStringValueOfRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="n">String</span> <span class="nf">convert</span><span class="o">(</span><span class="kt">int</span> <span class="n">i</span><span class="o">)</span> <span class="o">{</span>
|
||
<span class="n">String</span> <span class="n">s</span><span class="o">;</span>
|
||
<span class="n">s</span> <span class="o">=</span> <span class="s">"a"</span> <span class="o">+</span> <span class="n">String</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="n">i</span><span class="o">);</span> <span class="c1">// not required</span>
|
||
<span class="n">s</span> <span class="o">=</span> <span class="s">"a"</span> <span class="o">+</span> <span class="n">i</span><span class="o">;</span> <span class="c1">// preferred approach</span>
|
||
<span class="k">return</span> <span class="n">s</span><span class="o">;</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/UselessStringValueOf"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="usestringbufferforstringappends">UseStringBufferForStringAppends</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.1</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>The use of the ‘+=’ operator for appending strings causes the JVM to create and use an internal StringBuffer.
|
||
If a non-trivial number of these concatenations are being used then the explicit use of a StringBuilder or
|
||
threadsafe StringBuffer is recommended to avoid this.</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/UseStringBufferForStringAppendsRule.java">net.sourceforge.pmd.lang.java.rule.performance.UseStringBufferForStringAppendsRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="o">{</span>
|
||
<span class="kt">void</span> <span class="nf">bar</span><span class="o">()</span> <span class="o">{</span>
|
||
<span class="n">String</span> <span class="n">a</span><span class="o">;</span>
|
||
<span class="n">a</span> <span class="o">=</span> <span class="s">"foo"</span><span class="o">;</span>
|
||
<span class="n">a</span> <span class="o">+=</span> <span class="s">" bar"</span><span class="o">;</span>
|
||
<span class="c1">// better would be:</span>
|
||
<span class="c1">// StringBuilder a = new StringBuilder("foo");</span>
|
||
<span class="c1">// a.append(" bar");</span>
|
||
<span class="o">}</span>
|
||
<span class="o">}</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/UseStringBufferForStringAppends"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
<h2 id="usestringbufferlength">UseStringBufferLength</h2>
|
||
|
||
<p><strong>Since:</strong> PMD 3.4</p>
|
||
|
||
<p><strong>Priority:</strong> Medium (3)</p>
|
||
|
||
<p>Use StringBuffer.length() to determine StringBuffer length rather than using StringBuffer.toString().equals(“”)
|
||
or StringBuffer.toString().length() == …</p>
|
||
|
||
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/master/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/UseStringBufferLengthRule.java">net.sourceforge.pmd.lang.java.rule.performance.UseStringBufferLengthRule</a></p>
|
||
|
||
<p><strong>Example(s):</strong></p>
|
||
|
||
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">StringBuffer</span> <span class="n">sb</span> <span class="o">=</span> <span class="k">new</span> <span class="n">StringBuffer</span><span class="o">();</span>
|
||
|
||
<span class="k">if</span> <span class="o">(</span><span class="n">sb</span><span class="o">.</span><span class="na">toString</span><span class="o">().</span><span class="na">equals</span><span class="o">(</span><span class="s">""</span><span class="o">))</span> <span class="o">{}</span> <span class="c1">// inefficient</span>
|
||
|
||
<span class="k">if</span> <span class="o">(</span><span class="n">sb</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">==</span> <span class="mi">0</span><span class="o">)</span> <span class="o">{}</span> <span class="c1">// preferred</span>
|
||
</code></pre></div></div>
|
||
|
||
<p><strong>Use this rule by referencing it:</strong></p>
|
||
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt"><rule</span> <span class="na">ref=</span><span class="s">"category/java/performance.xml/UseStringBufferLength"</span> <span class="nt">/></span>
|
||
</code></pre></div></div>
|
||
|
||
|
||
|
||
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