User Guide

180 Chapter 5: ActionScript Core Language Elements
interface
Availability
Flash Player 6.
Usage
interface InterfaceName [extends InterfaceName ] {}
Description
Keyword; defines an interface. An interface is similar to a class, with the following
important differences:
• Interfaces contain only declarations of methods, not their implementation. That is, every class
that implements an interface must provide an implementation for each method declared in
the interface.
• Only public members are allowed in an interface definition; instance and class members are
not permitted.
• The get and set statements are not allowed in interface definitions.
FFor more information, see “Creating and using interfaces” on page 58.
Example
The following example shows several ways to define and implement interfaces:
(in top-level package .as files Ia, B, C, Ib, D, Ic, E)
// filename Ia.as
interface Ia
{
function k():Number; // method declaration only
function n(x:Number):Number; // without implementation
}
// filename B.as
class B implements Ia
{
function k():Number {return 25;}
function n(x:Number):Number {return x+5;}
}
// script file
var mvar:B = new B();
trace(mvar.k()); // 25
trace(mvar.n(7)); // 12
// filename c.as
class C implements Ia
{
function k():Number {return 25;}
} // error: class must implement all interface methods
// filename Ib.as
interface Ib
{
CHAPTER 5
ActionScript Core Language Elements