ActionScript 3.0 Design Patterns

240 | Chapter 6: Composite Pattern

Calculating the Total Weight of the Airplane

Line 56 of theMainclass shown in Example 6-25 calls thegetWeight( )method on the

root node of the airplane. The following output is the result of this statement.

Weight of airplane: 2100

ThegetWeight( )method calculates the weight iteratively by adding the weights of all

components in the airplane structure. This is a very powerful way of keeping track of

an overall parameter in a comple xcomposite structure. If this airplane were used in a

game, the weight is essential to craft realistic movement dynamics using motion

physics. The weight of the plane can change dynamically. For example, the plane

could be carrying passengers, bombs, and a fuel tank. Adding passengers will

increase weight; dropping bombs will reduce weight, and flight will progressively

reduce weight by using up fuel. ThegetWeight( )method will work exactly the same

way if we extend the airplane to add and remove other components such as passen-

gers, fuel, etc.

31 leftWing.scaleX = -1; // flip on vertical axis

32 leftWing.x = -20; leftWing.y = 50;

33 fuselage.addChild(leftWing);

34

35 // add engine to right wing

36 var rightEngine:Component = new Engine(300, 0);

37 rightEngine.x = 50; rightEngine.y = -20;

38 rightWing.addChild(rightEngine);

39

40 // add engine to left wing

41 var lefttEngine:Component = new Engine(300, 0);

42 lefttEngine.x = 50; lefttEngine.y = -20;

43 leftWing.addChild(lefttEngine);

44

45 // add tail wing on the right

46 var leftTailWing:Component = new TailWing(50, 0);

47 leftTailWing.scaleX = -1; // flip on vertical axis

48 leftTailWing.x = -20; leftTailWing.y = 150;

49 fuselage.addChild(leftTailWing);

50

51 // add tail wing on the left

52 var rightTailWing:Component = new TailWing(50, 0);

53 rightTailWing.x = 20; rightTailWing.y = 150;

54 fuselage.addChild(rightTailWing);

55

56 trace('Weight of airplane: ' + airPlane.getWeight( ));

57 //total weight

58 }

59 }

60 }

Example 6-25. Main.as (continued)