Class EqualsTester

java.lang.Object
junit.framework.Assert
com.gargoylesoftware.base.testing.EqualsTester

public class EqualsTester extends junit.framework.Assert
EqualsTester is used to test the equals contract on objects. The contract as specified by java.lang.Object states that if A.equals(B) is true then B.equals(A) is also true. It also specifies that if A.equals(B) is true then A.hashCode() will equals B.hashCode().

It is also common practice to implement equals using an instanceof check which will result in false positives in some cases. Specifically, it will result in false positives when comparing against a subclass with the same values. For an in-depth discussion of the common problems when implementing the equals contract, refer to the book "Practical Java" by Peter Haggar

 // WRONG way of implementing equals
 public boolean equals( final Object object ) {
     if( object instanceof this ) {
        // do check
     }
     return false;
 }
 
The correct way to implement equals is as follows
 public boolean equals( final Object object ) {
     if( object != null invalid input: '&'invalid input: '&' object.getClass() == this.getClass() ) {
        // do check
     }
     return false;
 }
 
EqualsTester ensures that the equals() and hashCode() methods have been implemented correctly.

 final Object a = new Foo(4); // original object
 final Object b = new Foo(4); // another object that has the same values as the original
 final Object c = new Foo(5); // another object with different values
 final Object d = new Foo(4) {}; // a subclass of Foo with the same values as the original
 new EqualsTester(a, b, c, d);
 
Version:
$Revision: 1.4 $
  • Constructor Details

    • EqualsTester

      public EqualsTester(Object a, Object b, Object c, Object d)
      Perform the test. The act of instantiating one of these will run the test.
      Parameters:
      a - The object to be tested
      b - An object that is equal to A
      c - An object of the same class that is not equal to A. If it is not possible to create a different one then pass null.
      d - A subclass of A with the same values. If A is an instance of a final class then this must be null
  • Method Details

    • isClassFinal

      private boolean isClassFinal(Class clazz)
    • assertAEqualsA

      private void assertAEqualsA(Object a)
    • assertAEqualsB

      private void assertAEqualsB(Object a, Object b)
    • assertANotEqualC

      private void assertANotEqualC(Object a, Object c)
    • assertClassAndSubclass

      private void assertClassAndSubclass(Object a, Object d)
    • assertNotNull

      private void assertNotNull(Object object, String description)
    • assertNull

      private void assertNull(Object object, String description)
    • assertCAllowedToBeNull

      private void assertCAllowedToBeNull(Class clazz)
      C may not be null if it has a public non-default constructor or any setXX() methods
      Parameters:
      clazz -
    • assertSameClassAsA

      private void assertSameClassAsA(Object a, Object object, String name)
    • assertDDifferentClassThanA

      private void assertDDifferentClassThanA(Object a, Object d)
    • assertAEqualsNull

      private void assertAEqualsNull(Object a)