Class EqualsHashCodeCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public class EqualsHashCodeCheck
    extends AbstractCheck

    Checks that classes that either override equals() or hashCode() also overrides the other. This check only verifies that the method declarations match Object.equals(Object) and Object.hashCode() exactly to be considered an override. This check does not verify invalid method names, parameters other than Object, or anything else.

    Rationale: The contract of equals() and hashCode() requires that equal objects have the same hashCode. Therefore, whenever you override equals() you must override hashCode() to ensure that your class can be used in hash-based collections.

    To configure the check:

     <module name="EqualsHashCode"/>
     

    Example:

     public static class Example1 {
         public int hashCode() {
             // code
         }
         public boolean equals(String o) { // violation, overloaded implementation of 'equals'
             // code
         }
     }
     public static class Example2 {
         public boolean equals(Object o) { // violation, no 'hashCode'
             // code
         }
         public boolean equals(String o) {
             // code
         }
     }
     public static class Example3 {
         public int hashCode() {
             // code
         }
         public boolean equals(Object o) { // OK
             // code
         }
         public boolean equals(String o) {
             // code
         }
     }
     public static class Example4 {
         public int hashCode() {
             // code
         }
         public boolean equals(java.lang.Object o) { // OK
             // code
        }
     }
     public static class Example5 {
         public static int hashCode(int i) {
             // code
         }
         public boolean equals(Object o) { // violation, overloaded implementation of 'hashCode'
             // code
         }
     }
     public static class Example6 {
         public int hashCode() { // violation, overloaded implementation of 'equals'
             // code
         }
         public static boolean equals(Object o, Object o2) {
             // code
         }
     }
     

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • equals.noEquals
    • equals.noHashCode
    Since:
    3.0
    • Method Detail

      • getAcceptableTokens

        public int[] getAcceptableTokens()
        Description copied from class: AbstractCheck
        The configurable token set. Used to protect Checks against malicious users who specify an unacceptable token set in the configuration file. The default implementation returns the check's default tokens.
        Specified by:
        getAcceptableTokens in class AbstractCheck
        Returns:
        the token set this check is designed for.
        See Also:
        TokenTypes
      • beginTree

        public void beginTree​(DetailAST rootAST)
        Description copied from class: AbstractCheck
        Called before the starting to process a tree. Ideal place to initialize information that is to be collected whilst processing a tree.
        Overrides:
        beginTree in class AbstractCheck
        Parameters:
        rootAST - the root of the tree
      • isEqualsMethod

        private static boolean isEqualsMethod​(DetailAST ast)
        Determines if an AST is a valid Equals method implementation.
        Parameters:
        ast - the AST to check
        Returns:
        true if the {code ast} is a Equals method.
      • isHashCodeMethod

        private static boolean isHashCodeMethod​(DetailAST ast)
        Determines if an AST is a valid HashCode method implementation.
        Parameters:
        ast - the AST to check
        Returns:
        true if the {code ast} is a HashCode method.
      • isObjectParam

        private static boolean isObjectParam​(DetailAST paramNode)
        Determines if an AST is a formal param of type Object.
        Parameters:
        paramNode - the AST to check
        Returns:
        true if firstChild is a parameter of an Object type.
      • finishTree

        public void finishTree​(DetailAST rootAST)
        Description copied from class: AbstractCheck
        Called after finished processing a tree. Ideal place to report on information collected whilst processing a tree.
        Overrides:
        finishTree in class AbstractCheck
        Parameters:
        rootAST - the root of the tree