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Trail: Learning the Java Language
Lesson: Classes, Interfaces, and Packages

## Using an Interface as a Type

> When you define a new interface, you are in essence defining a new reference data type. You can use interface names anywhere you can use any other data type name.

> For example, the `AlarmClock` class uses the `Sleeper` type in two places:

> - To declare an array of `Sleeper`s (shown in bold):

>   >     private Sleeper[] sleepers = new Sleeper[MAX_CAPACITY];

> - As an argument to `letMeSleepFor` (shown in bold):

>   >     private boolean letMeSleepFor(Sleeper theSleeper, int time)
>   >     {
>   >     . . .
>   >     }

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