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» Suppressing warnings
<a
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<div class="post-header">
<h1 class="post-title-main">Suppressing warnings</h1>
</div>
<div class="post-content" data-github-edit-url="https://github.com/pmd/pmd/blob/main/docs/pages/pmd/userdocs/suppressing_warnings.md">
<div class="summary">Learn how to suppress some rule violations, from the source code using annotations or comments, or globally from the ruleset</div>
<details id="inline-toc-details">
<summary>Table of Contents</summary>
<div id="inline-toc"><!-- empty, move TOC here when screen size too small --></div>
</details>
<p>PMD provides several methods by which Rule violations can be suppressed.
Follow these steps to help you determine which expression method works best
for you:</p>
<ol>
<li>
<p>Is the thing you need to suppress universally appealing to other
users of PMD, or is it a false positive? Can you modify the Rule to
support this specific suppression via a configuration property, or to
fix the false positive? If you can do this, then please do so, and
submit a patch back to the PMD project. Since PMD is built by users
for users, your help would be greatly appreciated by everyone. If you
cannot…</p>
</li>
<li>
<p>Can you use Annotations or the NOPMD marker to work around your
particular issue on a case by case basis? If not…</p>
</li>
<li>
<p>Can a regular expression matching the violation message work
around your particular issue? If not…</p>
</li>
<li>
<p>Can a XPath query on the violation node work around your particular
issue? If not…</p>
</li>
<li>
<p>Your last and final option is to see the first point about
changing the Rule, but you do not need to submit a patch back to the
PMD project.</p>
</li>
</ol>
<p>If you need to modify the Rule, see <a href="pmd_userdocs_extending_writing_rules_intro.html">How to write a rule</a>.
Otherwise, the other suppression methods are explained in the following sections.</p>
<h2 id="annotations">Annotations</h2>
<p>When using Java 1.5 or later, you can use annotations to suppress PMD warnings, like this:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// This will suppress all the PMD warnings in this class</span>
<span class="nd">@SuppressWarnings</span><span class="o">(</span><span class="s">"PMD"</span><span class="o">)</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Bar</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="kt">int</span> <span class="n">foo</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre></div></div>
<p>When using Apex make sure to use single quotes instead of double quotes</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// This will suppress all the PMD warnings in this class</span>
<span class="nd">@SuppressWarnings</span><span class="o">(</span><span class="err">'</span><span class="no">PMD</span><span class="err">'</span><span class="o">)</span>
</code></pre></div></div>
<p>Or you can suppress one rule with an annotation like this:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// This will suppress UnusedLocalVariable warnings in this class</span>
<span class="nd">@SuppressWarnings</span><span class="o">(</span><span class="s">"PMD.UnusedLocalVariable"</span><span class="o">)</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Bar</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="kt">int</span> <span class="n">foo</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre></div></div>
<p>Multiple rules can be suppressed by providing multiple values, ie:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nd">@SuppressWarnings</span><span class="o">({</span><span class="s">"PMD.UnusedLocalVariable"</span><span class="o">,</span> <span class="s">"PMD.UnusedPrivateMethod"</span><span class="o">})</span>
</code></pre></div></div>
<p>For Apex, the syntax for this is slightly different:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nd">@SuppressWarnings</span><span class="o">(</span><span class="err">'</span><span class="no">PMD</span><span class="o">.</span><span class="na">UnusedLocalVariable</span><span class="o">,</span> <span class="no">PMD</span><span class="o">.</span><span class="na">UnusedPrivateMethod</span><span class="err">'</span><span class="o">)</span>
</code></pre></div></div>
<p>PMD Java also obeys the JDK annotation @SuppressWarnings(“unused”), which will apply to all rules in the unused ruleset.</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// This will suppress UnusedLocalVariable and UnusedPrivateMethod warnings in this class</span>
<span class="nd">@SuppressWarnings</span><span class="o">(</span><span class="s">"unused"</span><span class="o">)</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Bar</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="kt">int</span> <span class="n">foo</span><span class="o">;</span>
<span class="o">}</span>
<span class="kd">private</span> <span class="kt">void</span> <span class="nf">foobar</span><span class="o">(){}</span>
<span class="o">}</span>
</code></pre></div></div>
<h2 id="nopmd-comment">NOPMD comment</h2>
<p>Alternatively, you can tell PMD to ignore a specific line by using the “NOPMD” marker in a comment, like this:</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">Bar</span> <span class="o">{</span>
<span class="c1">// 'bar' is accessed by a native method, so we want to suppress warnings for it</span>
<span class="kd">private</span> <span class="kt">int</span> <span class="n">bar</span><span class="o">;</span> <span class="c1">//NOPMD</span>
<span class="o">}</span>
</code></pre></div></div>
<p>You can use whatever text string you want to suppress warnings, by using the <code class="language-plaintext highlighter-rouge">-suppressmarker</code> CLI option.
For example, here’s how to use <code class="language-plaintext highlighter-rouge">TURN_OFF_WARNINGS</code> as the suppressor:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="err">$</span> <span class="n">cat</span> <span class="nc">Foo</span><span class="o">.</span><span class="na">java</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="o">{</span>
<span class="kt">void</span> <span class="nf">bar</span><span class="o">()</span> <span class="o">{</span>
<span class="kt">int</span> <span class="n">x</span> <span class="o">=</span> <span class="mi">2</span><span class="o">;</span> <span class="c1">// TURN_OFF_WARNINGS</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="err">$</span> <span class="n">pmd</span> <span class="n">check</span> <span class="o">-</span><span class="n">d</span> <span class="nc">Foo</span><span class="o">.</span><span class="na">java</span> <span class="o">-</span><span class="n">f</span> <span class="n">text</span> <span class="o">-</span><span class="no">R</span> <span class="n">java</span><span class="o">-</span><span class="n">unusedcode</span> <span class="o">--</span><span class="n">suppress</span><span class="o">-</span><span class="n">marker</span> <span class="no">TURN_OFF_WARNINGS</span>
<span class="nc">No</span> <span class="n">problems</span> <span class="n">found</span><span class="o">!</span>
<span class="nc">UnusedLocalVariable</span> <span class="n">rule</span> <span class="n">violation</span> <span class="n">suppressed</span> <span class="n">by</span> <span class="c1">//NOPMD in /home/tom/pmd/pmd/bin/Foo.java</span>
</code></pre></div></div>
<p>Note that PMD expects the //NOPMD marker to be on the same line as the violation. So, for
example, if you want to suppress an “empty <code class="language-plaintext highlighter-rouge">if</code> statement” warning, you’ll need to place it on
the line containing the <code class="language-plaintext highlighter-rouge">if</code> keyword, e.g.:</p>
<div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="err">$</span> <span class="n">cat</span> <span class="o">~/</span><span class="n">tmp</span><span class="o">/</span><span class="nc">Foo</span><span class="o">.</span><span class="na">java</span>
<span class="kd">public</span> <span class="kd">class</span> <span class="nc">Foo</span> <span class="o">{</span>
<span class="kt">void</span> <span class="nf">bar</span><span class="o">()</span> <span class="o">{</span>
<span class="kt">int</span> <span class="n">x</span> <span class="o">=</span> <span class="mi">42</span><span class="o">;</span>
<span class="k">if</span> <span class="o">(</span><span class="n">x</span> <span class="o">&gt;</span> <span class="mi">5</span><span class="o">)</span> <span class="o">{</span> <span class="c1">// NOPMD</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="o">}</span>
<span class="err">$</span> <span class="n">java</span> <span class="n">net</span><span class="o">.</span><span class="na">sourceforge</span><span class="o">.</span><span class="na">pmd</span><span class="o">.</span><span class="na">PMD</span> <span class="o">-</span><span class="n">d</span> <span class="o">~/</span><span class="n">tmp</span><span class="o">/</span><span class="nc">Foo</span><span class="o">.</span><span class="na">java</span> <span class="o">-</span><span class="n">f</span> <span class="n">text</span> <span class="o">-</span><span class="no">R</span> <span class="n">java</span><span class="o">-</span><span class="n">basic</span>
<span class="nc">No</span> <span class="n">problems</span> <span class="n">found</span><span class="o">!</span>
</code></pre></div></div>
<p>A message placed after the NOPMD marker will get placed in the report, e.g.:</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="k">try</span> <span class="o">{</span>
<span class="n">bar</span><span class="o">();</span>
<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="nc">FileNotFoundException</span> <span class="n">e</span><span class="o">)</span> <span class="o">{}</span> <span class="c1">// NOPMD - this surely will never happen</span>
<span class="o">}</span>
<span class="o">}</span>
</code></pre></div></div>
<h2 id="xpath-and-regex-message-suppression">XPath and Regex message suppression</h2>
<p>If a particular rule consistently reports a warning in a particular context, you can fall
back to disabling the rule for all these contexts using one of two rule properties
that are defined on every rule. Depending on what you’re after, you can suppress
violations for <strong>specific messages</strong> using regular expressions, or <strong>specific nodes</strong>
using an XPath expression.</p>
<h3 id="the-property-violationsuppressregex">The property <code class="language-plaintext highlighter-rouge">violationSuppressRegex</code></h3>
<p>This property defines a regular expression to match against the
message of the violation. If the regular expression matches,
then the violation will be suppressed.</p>
<p>For example, to suppress reporting specifically named parameters which
are unused:</p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;rule</span> <span class="na">ref=</span><span class="s">"rulesets/java/unusedcode.xml/UnusedFormalParameter"</span><span class="nt">&gt;</span>
<span class="nt">&lt;properties&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"violationSuppressRegex"</span> <span class="na">value=</span><span class="s">".*'mySpecialParameterName'.*"</span><span class="nt">/&gt;</span>
<span class="nt">&lt;/properties&gt;</span>
<span class="nt">&lt;/rule&gt;</span>
</code></pre></div></div>
<p>Note for message based suppression to work, you must know how to write
a regular expression that matches the message of violations you wish to
suppress. Regular expressions are explained in the JavaDoc for standard
Java class java.util.regex.Pattern.</p>
<p>This technique of course relies on how the rule’s message is implemented.
Some rules always report the same message, in which case this property is
of no use.</p>
<h3 id="the-property-violationsuppressxpath">The property <code class="language-plaintext highlighter-rouge">violationSuppressXPath</code></h3>
<p>This property defines an XPath query to be executed <em>using the
violation node as the context node</em>. If the XPath query matches anything,
then the violation will be suppressed. Note that the query shouldn’t be finding
the violation nodes to suppress, but rather, finding a non-empty sequence of nodes
when evaluated with the violation node as a context node.</p>
<p>The XPath version used by those queries is XPath 3.1 since PMD 7. Before then XPath 1.0 was used.</p>
<p>For example, to suppress reporting specifically “String” parameters which are unused:</p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;rule</span> <span class="na">ref=</span><span class="s">"rulesets/java/unusedcode.xml/UnusedFormalParameter"</span><span class="nt">&gt;</span>
<span class="nt">&lt;properties&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"violationSuppressXPath"</span> <span class="na">value=</span><span class="s">".[typeIs('java.lang.String')]"</span><span class="nt">/&gt;</span>
<span class="nt">&lt;/properties&gt;</span>
<span class="nt">&lt;/rule&gt;</span>
</code></pre></div></div>
<p>Note the use of <code class="language-plaintext highlighter-rouge">.</code> to refer to the context node. Using <code class="language-plaintext highlighter-rouge">//</code> at the start of the
expression should be avoided, as it would test all nodes in the file, and suppress
more violations than expected.</p>
<p>Another example, to suppress violations occurring in classes whose name contains <code class="language-plaintext highlighter-rouge">Bean</code>:</p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"violationSuppressXPath"</span> <span class="na">value=</span><span class="s">"./ancestor-or-self::ClassDeclaration[contains(@SimpleName, 'Bean')]"</span><span class="nt">/&gt;</span>
</code></pre></div></div>
<p>And an example to suppress violations occurring in <code class="language-plaintext highlighter-rouge">equals</code> or <code class="language-plaintext highlighter-rouge">hashCode</code> methods:</p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"violationSuppressXPath"</span> <span class="na">value=</span><span class="s">"./ancestor-or-self::MethodDeclaration[@Name = ('equals', 'hashCode')]"</span><span class="nt">/&gt;</span>
</code></pre></div></div>
<p>Note the use of a sequence comparison, which tests for true if any member of one sequence matches any other member of the other.
Here this test is true if the <code class="language-plaintext highlighter-rouge">@Name</code> attribute is any of the given names.</p>
<p>You can also use regex for string comparison. The next example suppresses violations in classes ending with <code class="language-plaintext highlighter-rouge">Bean</code>:</p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"violationSuppressXPath"</span> <span class="na">value=</span><span class="s">"./ancestor-or-self::ClassDeclaration[matches(@SimpleName, '^.*Bean$')]"</span><span class="nt">/&gt;</span>
</code></pre></div></div>
<p>Note here the usage of the <code class="language-plaintext highlighter-rouge">./ancestor-or-self::</code> axis instead of <code class="language-plaintext highlighter-rouge">//</code>. The latter would match
any ClassDeclaration in the file, while the former matches only class
declaration nodes that <em>enclose the violation node</em>, which is usually what you’d want.</p>
<p>Note the context node in this expression is the node the violation was reported on. Different
rules report on different nodes, for instance, <a href="pmd_rules_java_bestpractices.html#unusedformalparameter"><code class="language-plaintext highlighter-rouge">UnusedFormalParameter</code></a> reports
on the <code class="language-plaintext highlighter-rouge">ASTVariableId</code> for the parameter, and <a href="pmd_rules_java_bestpractices.html#missingoverride"><code class="language-plaintext highlighter-rouge">MissingOverride</code></a> reports on
the <code class="language-plaintext highlighter-rouge">ASTMethodDeclaration</code> node. You have to take this into account when using the context node directly,
although many <code class="language-plaintext highlighter-rouge">violationSuppressXPath</code> expressions will check for some ancestor node like an enclosing class or method,
instead of testing the context node directly.
The nodes which a rule reports on can only be determined by looking at the implementation of the rule.</p>
<p>Note for XPath based suppression to work, you must know how to write
an XPath query that matches the AST structure of the nodes of the
violations you wish to suppress. XPath queries are explained in
<a href="pmd_userdocs_extending_writing_xpath_rules.html">XPath Rule tutorial</a>.</p>
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