Package com.qulice.checkstyle

Class DiamondOperatorCheck

java.lang.Object
com.puppycrawl.tools.checkstyle.AbstractAutomaticBean
com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
com.puppycrawl.tools.checkstyle.api.AbstractCheck
com.qulice.checkstyle.DiamondOperatorCheck
All Implemented Interfaces:
com.puppycrawl.tools.checkstyle.api.Configurable, com.puppycrawl.tools.checkstyle.api.Contextualizable
public final class DiamondOperatorCheck extends com.puppycrawl.tools.checkstyle.api.AbstractCheck
Checks if possible to use Diamond operator in generic instances creation.

Check is performed for variable declarations. Since parameterized types are invariant in generics, Diamond operator should always be used in variable declarations.

For example, 

     private List<Number> numbers = new ArrayList<Integer>(); // error
will return compilation error (because ArrayList<Integer> is not a subclass of List<Number>).

Hence, the only possible way to create a generic instance is copying type arguments from the variable declaration. 

     private List<Number> numbers = new ArrayList<Number>();
In that case, Diamond Operator should always be used. 
     private List<Number> numbers = new ArrayList<>();

Exceptions to the rule above are wildcards, with them it's possible to have different type parameters for left and right parts of variable declaration. 

     // will compile
     private List<? extends Number> numbers = new ArrayList<Integer>();
     private List<? super Integer> list = new ArrayList<Number>();
Although, this is not considered as good codestyle, so it's better to use diamond operator here either.

Since:
0.17

  • Nested Class Summary

    Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.AbstractAutomaticBean

    com.puppycrawl.tools.checkstyle.AbstractAutomaticBean.OutputStreamOptions

  • Constructor Summary

    Constructors
    Constructor
    Description
    DiamondOperatorCheck()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    int[]
    getAcceptableTokens()
     
    int[]
    getDefaultTokens()
     
    int[]
    getRequiredTokens()
     
    void
    visitToken(com.puppycrawl.tools.checkstyle.api.DetailAST node)
     

    Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractCheck

    beginTree, clearViolations, destroy, finishTree, getFileContents, getFilePath, getLine, getLineCodePoints, getLines, getTabWidth, getTokenNames, getViolations, init, isCommentNodesRequired, leaveToken, log, log, log, setFileContents, setTabWidth, setTokens

    Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter

    finishLocalSetup, getCustomMessages, getId, getMessageBundle, getSeverity, getSeverityLevel, setId, setSeverity

    Methods inherited from class com.puppycrawl.tools.checkstyle.AbstractAutomaticBean

    configure, contextualize, getConfiguration, setupChild

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • DiamondOperatorCheck

      public DiamondOperatorCheck()

  • Method Details

    • getDefaultTokens

      public int[] getDefaultTokens()
      Specified by:
      getDefaultTokens in class com.puppycrawl.tools.checkstyle.api.AbstractCheck

    • getAcceptableTokens

      public int[] getAcceptableTokens()
      Specified by:
      getAcceptableTokens in class com.puppycrawl.tools.checkstyle.api.AbstractCheck

    • getRequiredTokens

      public int[] getRequiredTokens()
      Specified by:
      getRequiredTokens in class com.puppycrawl.tools.checkstyle.api.AbstractCheck

    • visitToken

      public void visitToken(com.puppycrawl.tools.checkstyle.api.DetailAST node)
      Overrides:
      visitToken in class com.puppycrawl.tools.checkstyle.api.AbstractCheck