Package com.puppycrawl.tools.checkstyle.checks.coding

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

    • Field Detail

      • MSG_KEY_HASHCODE

        public static final java.lang.String MSG_KEY_HASHCODE
        A key is pointing to the warning message text in "messages.properties" file.
        See Also:
        Constant Field Values

      • MSG_KEY_EQUALS

        public static final java.lang.String MSG_KEY_EQUALS
        A key is pointing to the warning message text in "messages.properties" file.
        See Also:
        Constant Field Values

    • Constructor Detail

      • EqualsHashCodeCheck

        public EqualsHashCodeCheck()

    • Method Detail

      • getDefaultTokens

        public int[] getDefaultTokens()
        Description copied from class: AbstractCheck
        Returns the default token a check is interested in. Only used if the configuration for a check does not define the tokens.
        Specified by:
        getDefaultTokens in class AbstractCheck
        Returns:
        the default tokens
        See Also:
        TokenTypes

      • 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

      • getRequiredTokens

        public int[] getRequiredTokens()
        Description copied from class: AbstractCheck
        The tokens that this check must be registered for.
        Specified by:
        getRequiredTokens in class AbstractCheck
        Returns:
        the token set this must be registered 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

      • 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