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 $
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionprivate void
private void
assertAEqualsB
(Object a, Object b) private void
private void
assertANotEqualC
(Object a, Object c) private void
assertCAllowedToBeNull
(Class clazz) C may not be null if it has a public non-default constructor or any setXX() methodsprivate void
private void
private void
assertNotNull
(Object object, String description) private void
assertNull
(Object object, String description) private void
assertSameClassAsA
(Object a, Object object, String name) private boolean
isClassFinal
(Class clazz) Methods inherited from class junit.framework.Assert
assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertEquals, assertFalse, assertFalse, assertNotNull, assertNotNull, assertNotSame, assertNotSame, assertNull, assertNull, assertSame, assertSame, assertTrue, assertTrue, fail, fail, failNotEquals, failNotSame, failSame, format
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Constructor Details
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EqualsTester
Perform the test. The act of instantiating one of these will run the test.- Parameters:
a
- The object to be testedb
- An object that is equal to Ac
- 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
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Method Details
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isClassFinal
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assertAEqualsA
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assertAEqualsB
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assertANotEqualC
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assertClassAndSubclass
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assertNotNull
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assertNull
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assertCAllowedToBeNull
C may not be null if it has a public non-default constructor or any setXX() methods- Parameters:
clazz
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assertSameClassAsA
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assertDDifferentClassThanA
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assertAEqualsNull
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