The JavaTM Tutorial

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Trail: Learning the Java Language
Lesson: More Features of the Java Language

## Implementing the Sleeper Interface

> Implementing an Interface in the previous lesson already showed you how to implement an interface. Here, the `GUIClock` class implements one interface--`Sleeper`:

> >     public class GUIClock extends Applet implements Sleeper {
> >         . . .
> >         public void wakeUp() {
> >             // update the display
> >         }
> >     }

> Remember that when a class implements an interface, it is essentially signing a contract. The class must provide method implementations for all of the methods declared in the interface and its superinterfaces. Or, the class must be declared `abstract`. The method signature (the name and the number and type of arguments) for the method in the class must match the method signature as it appears in the interface.

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