ActionScript 3.0 Design Patterns

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Chapter 7
CHAPTER 7

Command Pattern 7

To command is to serve, nothing more and nothing

less.

—Andre Malraux

When you do the common things in life in an

uncommon way, you will command the attention of

the world.

—George Washington Carver

Create like a god, command like a king, work like a

slave.

—Constantin Brancusi

What Is the Command Pattern?

The command pattern allows a client to issue requests to an object without making

any assumptions about the request, or the receiving object. Think of the request as a

command sent to an object to engage in a known behavior. The straightforward way

to do this would be to create an instance of the object, and call the method that

implements the required command (or behavior). For example, let’s assume that

we’re building a house that allows computer control of many of its components such

as lights, doors, heating, etc. Let’s look at the code that would turn on a light bulb.

TheLightclass implements a method calledon( )that turns on a light. A client

would execute the following code to turn the light on.

var light = new Light( );

light.on( );

Let’s look at another command to open a door. In this case, thereceiverof the com-

mand is an instance of theDoorclass, which implements a method calledopen( )that

opens the front door.

var frontdoor = new Door( );

frontdoor.open( );