sun.com/docs/books/effective/index.html">Effective Java , by Joshua Bloch. In particular the rule for comparing
doubles,
floats, and arrays can be tricky. Also, making sure that
equals() and
hashCode() are consistent can be difficult.
Two Objects that compare as equals must generate the same hash code, but two Objects with the same hash code do not have to be equal.
All relevant fields should be included in the calculation of equals. Derived fields may be ignored. In particular, any field used in generating a hash code must be used in the equals method, and vice versa.
Typical use for the code is as follows:
public boolean equals(Object obj) { if (obj == null) { return false; } if (obj == this) { return true; } if (obj.getClass() != getClass()) { return false; } MyClass rhs = (MyClass) obj; return new EqualsBuilder() .appendSuper(super.equals(obj)) .append(field1, rhs.field1) .append(field2, rhs.field2) .append(field3, rhs.field3) .isEquals(); } Alternatively, there is a method that uses reflection to determine the fields to test. Because these fields are usually private, the method, reflectionEquals, uses AccessibleObject.setAccessible to change the visibility of the fields. This will fail under a security manager, unless the appropriate permissions are set up correctly. It is also slower than testing explicitly.
A typical invocation for this method would look like:
public boolean equals(Object obj) { return EqualsBuilder.reflectionEquals(this, obj); }
@author Apache Software Foundation
@author
Steve Downey
@author Gary Gregory
@author Pete Gieser
@author Arun Mammen Thomas
@author Oliver Sauder
@since 1.0
@version $Id: EqualsBuilder.java 925674 2010-03-20 20:20:26Z bayard $