What is the difference between identity and equality in OOP?

• identity: a variable holds the same instance as another variable.
• equality: two distinct objects can be used interchangeably. they often have the same id.

For example:

Integer a = new Integer(1);
Integer b = a;

a is identical to b.

Integer c =  new Integer(1);
Integer d = new Integer(1);

c is equal but not identical to d.

Of course, two identical variables are always equal.

In Java, equality is defined by the equals method. Keep in mind, if you implement equals you must also implement hashCode.

http://stackoverflow.com/questions/1692863/what-is-the-difference-between-identity-and-equality-in-oop