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Learning the Java Language
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Interfaces and Inheritance
Writing Final Classes and Methods
You can declare some or all of a class's methods
final.
You use the
final keyword in a method
declaration to indicate that the method cannot be overridden
by subclasses. The
Object class does this—a number
of its methods are
final.
You might wish to make a method final if it has an implementation
that should not be changed and it is critical to the consistent
state of the object. For example, you might want to make the
getFirstPlayer method in this
ChessAlgorithm class final:
class ChessAlgorithm {
enum ChessPlayer { WHITE, BLACK }
...
final ChessPlayer getFirstPlayer() {
return ChessPlayer.WHITE;
}
...
}
Methods called from constructors should generally be declared final.
If a constructor calls a non-final method, a subclass may redefine
that method with surprising or undesirable results.
Note that you can also declare an entire class final — this
prevents the class from being subclassed. This is particularly
useful, for example, when creating an immutable class like the String class.
