Java defines the equality operators == and != for testing reference equality but uses the Object.equals() method and its subclasses for testing abstract object equality. Naive programmers often confuse the intent of the == operation with that of the Object.equals() method. This confusion is frequently evident in the context of processing String processing objects.
As a general rule, use the Object.equals() method to check whether two objects are abstractly equal to each other and the equality operators == and != to test whether two references specifically refer to the same object. This latter test is referred to as referential equality. Also see MET09-J. Classes that define an equals() method must also define a hashCode() method .
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