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Trail: Learning the Java Language
Lesson: Interfaces and Inheritance
Section: Inheritance
Interfaces and Inheritance
Interfaces
Defining an Interface
Implementing an Interface
Using an Interface as a Type
Rewriting Interfaces
Summary of Interfaces
Questions and Exercises
Inheritance
Overriding and Hiding Methods
Hiding Fields
Using the Keyword super
Object as a Superclass
Writing Final Classes and Methods
Abstract Methods and Classes
Summary of Inheritance
Questions and Exercises
Home Page > Learning the Java Language > 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.

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