Java Reference
In-Depth Information
10.6.1 An Actor interface
Code 10.9 shows Actor defined as an interface type.
Code 10.9
The Actor interface
* The interface to be extended by any class wishing
* to participate in the simulation.
public interface Actor
* Perform the actor's regular behavior.
* @param newActors A list for receiving newly created actors.
void act(List<Actor> newActors);
* Is the actor still active?
* @return true if still active, false if not.
boolean isActive();
Java interfaces have a number of significant features:
A Java interface
is a specification of
a type (in the form
of a type name and
a set of methods)
that does not
define any imple-
mentation for the
The keyword interface is used instead of class in the header of the declaration.
All methods in an interface are abstract; no method bodies are permitted. The abstract
keyword is not needed, therefore.
Interfaces do not contain any constructors.
All method headers in an interface have public visibility, so the public keyword is not needed.
Only public constant class fields ( static and final ) are allowed in an interface. The
public , static , and final keywords may be omitted, therefore.
A class can inherit from an interface in a similar way to that for inheriting from a class.
However, Java uses a different keyword— implements —for inheriting interfaces.
A class is said to implement an interface if it includes an implements clause in its class header.
For instance:
public class Fox extends Animal implements Drawable
// Body of class omitted.
As in this case, if a class both extends a class and implements an interface, then the extends
clause must be written first in the class header.
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