ActionScript 3.0 Design Patterns.pdf - VideoTutorials-bg.com

Example 6-1. Component.as (continued)
}
}
}
throw new IllegalOperationError
("remove operation not supported");
public function getChild(n:int):Component
{
throw new IllegalOperationError
("getChild operation not supported");
return null;
}
// ABSTRACT Method (must be overridden in a subclass)
public function operation( ):void {}
The Component class should behave as an abstract class and should not be instantiated.
It also defines the abstract interface for managing child components, and provides
default implementations for the add(c:Component), remove(c:Component) and
getChild(n:int) methods. The default implementations for these methods are
designed for leaf nodes and will raise an exception by throwing an
IllegalOperationError. This should be the case as leaf nodes cannot have children
and should not implement operations that deal with child nodes. In addition, the
operation( ) method is defined as an abstract method without implementation. It is
left up to the classes that subclass Component to provide an implementation for it.
Example 6-2. Leaf.as
package
{
public class Leaf extends Component
{
private var sName:String;
}
}
public function Leaf(sNodeName:String)
{
this.sName = sNodeName;
}
override public function operation( ):void
{
trace(this.sName);
}
The Leaf class extends the Component class. It declares a property called sName that
holds the name of the leaf. It also implements a parameterized constructor that takes
a string value that’s then set to the sName property. It implements the operation( )
208 | Chapter 6: Composite Pattern