Finish Future approach

docs/pages/pmd/rules/java.md

@@ -117,6 +117,7 @@ folder: pmd/rules
 *   [UnnecessaryLocalBeforeReturn](pmd_rules_java_codestyle.html#unnecessarylocalbeforereturn): Avoid the creation of unnecessary local variables
 *   [UnnecessaryModifier](pmd_rules_java_codestyle.html#unnecessarymodifier): Fields in interfaces and annotations are automatically 'public static final', and methods are 'pu...
 *   [UnnecessaryReturn](pmd_rules_java_codestyle.html#unnecessaryreturn): Avoid the use of unnecessary return statements.
+*   [UseDiamondOperator](pmd_rules_java_codestyle.html#usediamondoperator): Use the diamond operator to let the type be inferred automatically. With the Diamond operator it ...
 *   [UselessParentheses](pmd_rules_java_codestyle.html#uselessparentheses): Useless parentheses should be removed.
 *   [UselessQualifiedThis](pmd_rules_java_codestyle.html#uselessqualifiedthis): Reports qualified this usages in the same class.
 *   [UseUnderscoresInNumericLiterals](pmd_rules_java_codestyle.html#useunderscoresinnumericliterals): Since Java 1.7, numeric literals can use underscores to separate digits. This rule enforces that ...

docs/pages/pmd/rules/java/codestyle.md

@@ -5,7 +5,7 @@ permalink: pmd_rules_java_codestyle.html
 folder: pmd/rules/java
 sidebaractiveurl: /pmd_rules_java.html
 editmepath: ../pmd-java/src/main/resources/category/java/codestyle.xml
-keywords: Code Style, AbstractNaming, AtLeastOneConstructor, AvoidDollarSigns, AvoidFinalLocalVariable, AvoidPrefixingMethodParameters, AvoidProtectedFieldInFinalClass, AvoidProtectedMethodInFinalClassNotExtending, AvoidUsingNativeCode, BooleanGetMethodName, CallSuperInConstructor, ClassNamingConventions, CommentDefaultAccessModifier, ConfusingTernary, ControlStatementBraces, DefaultPackage, DontImportJavaLang, DuplicateImports, EmptyMethodInAbstractClassShouldBeAbstract, ExtendsObject, FieldDeclarationsShouldBeAtStartOfClass, FieldNamingConventions, ForLoopShouldBeWhileLoop, ForLoopsMustUseBraces, FormalParameterNamingConventions, GenericsNaming, IdenticalCatchBranches, IfElseStmtsMustUseBraces, IfStmtsMustUseBraces, LinguisticNaming, LocalHomeNamingConvention, LocalInterfaceSessionNamingConvention, LocalVariableCouldBeFinal, LocalVariableNamingConventions, LongVariable, MDBAndSessionBeanNamingConvention, MethodArgumentCouldBeFinal, MethodNamingConventions, MIsLeadingVariableName, NoPackage, UseUnderscoresInNumericLiterals, OnlyOneReturn, PackageCase, PrematureDeclaration, RemoteInterfaceNamingConvention, RemoteSessionInterfaceNamingConvention, ShortClassName, ShortMethodName, ShortVariable, SuspiciousConstantFieldName, TooManyStaticImports, UnnecessaryAnnotationValueElement, UnnecessaryConstructor, UnnecessaryFullyQualifiedName, UnnecessaryLocalBeforeReturn, UnnecessaryModifier, UnnecessaryReturn, UselessParentheses, UselessQualifiedThis, VariableNamingConventions, WhileLoopsMustUseBraces
+keywords: Code Style, AbstractNaming, AtLeastOneConstructor, AvoidDollarSigns, AvoidFinalLocalVariable, AvoidPrefixingMethodParameters, AvoidProtectedFieldInFinalClass, AvoidProtectedMethodInFinalClassNotExtending, AvoidUsingNativeCode, BooleanGetMethodName, CallSuperInConstructor, ClassNamingConventions, CommentDefaultAccessModifier, ConfusingTernary, ControlStatementBraces, DefaultPackage, DontImportJavaLang, DuplicateImports, EmptyMethodInAbstractClassShouldBeAbstract, ExtendsObject, FieldDeclarationsShouldBeAtStartOfClass, FieldNamingConventions, ForLoopShouldBeWhileLoop, ForLoopsMustUseBraces, FormalParameterNamingConventions, GenericsNaming, IdenticalCatchBranches, IfElseStmtsMustUseBraces, IfStmtsMustUseBraces, LinguisticNaming, LocalHomeNamingConvention, LocalInterfaceSessionNamingConvention, LocalVariableCouldBeFinal, LocalVariableNamingConventions, LongVariable, MDBAndSessionBeanNamingConvention, MethodArgumentCouldBeFinal, MethodNamingConventions, MIsLeadingVariableName, NoPackage, UseUnderscoresInNumericLiterals, OnlyOneReturn, PackageCase, PrematureDeclaration, RemoteInterfaceNamingConvention, RemoteSessionInterfaceNamingConvention, ShortClassName, ShortMethodName, ShortVariable, SuspiciousConstantFieldName, TooManyStaticImports, UnnecessaryAnnotationValueElement, UnnecessaryConstructor, UnnecessaryFullyQualifiedName, UnnecessaryLocalBeforeReturn, UnnecessaryModifier, UnnecessaryReturn, UseDiamondOperator, UselessParentheses, UselessQualifiedThis, VariableNamingConventions, WhileLoopsMustUseBraces
 language: Java
 ---
 <!-- DO NOT EDIT THIS FILE. This file is generated from file ../pmd-java/src/main/resources/category/java/codestyle.xml. -->
@@ -2072,6 +2072,44 @@ public class Foo {
 <rule ref="category/java/codestyle.xml/UnnecessaryReturn" />
 ```
 
+## UseDiamondOperator
+
+**Since:** PMD 6.11.0
+
+**Priority:** Medium (3)
+
+**Minimum Language Version:** Java 1.7
+
+Use the diamond operator to let the type be inferred automatically. With the Diamond operator it is possible
+to avoid duplication of the type parameters.
+Instead, the compiler is now able to infer the parameter types for constructor calls,
+which makes the code also more readable.
+
+**This rule is defined by the following XPath expression:**
+``` xpath
+//VariableInitializer
+//PrimaryExpression[not(PrimarySuffix)]
+[not(ancestor::ArgumentList)]
+/PrimaryPrefix/AllocationExpression[ClassOrInterfaceType[@AnonymousClass='false']/TypeArguments//ReferenceType[not(.//TypeArguments)]]
+|
+//StatementExpression[AssignmentOperator][PrimaryExpression/PrimaryPrefix[not(Expression)]]
+//PrimaryExpression[not(PrimarySuffix)]
+[not(ancestor::ArgumentList)]
+/PrimaryPrefix/AllocationExpression[ClassOrInterfaceType[@AnonymousClass='false']/TypeArguments//ReferenceType[not(.//TypeArguments)]]
+```
+
+**Example(s):**
+
+``` java
+List<String> strings = new ArrayList<String>(); // unnecessary duplication of type parameters
+List<String> stringsWithDiamond = new ArrayList<>(); // using the diamond operator is more concise
+```
+
+**Use this rule by referencing it:**
+``` xml
+<rule ref="category/java/codestyle.xml/UseDiamondOperator" />
+```
+
 ## UselessParentheses
 
 **Since:** PMD 5.0