设计模式-策略模式

1. publicabstractclassDuck{
2. FlyBehaviorflyBehavior;
3. QuackBehaviorquackBehavior;
5. publicDuck(){
6. }
8. publicvoidsetFlyBehavior(FlyBehaviorfb){
9. flyBehavior=fb;
10. }
12. publicvoidsetQuackBehavior(QuackBehaviorqb){
13. quackBehavior=qb;
14. }
16. abstractvoiddisplay();
18. publicvoidperformFly(){
19. flyBehavior.fly();
20. }
22. publicvoidperformQuack(){
23. quackBehavior.quack();
24. }
26. publicvoidswim(){
27. System.out.println("Allducksfloat,evendecoys!");
28. }
29. }

1. publicinterfaceFlyBehavior{
2. publicvoidfly();
3. }

1. publicinterfaceQuackBehavior{
2. publicvoidquack();
3. }

1. publicclassFlyWithWingsimplementsFlyBehavior{
2. publicvoidfly(){
3. System.out.println("I'mflying!!");
4. }
5. }

1. publicclassRedHeadDuckextendsDuck{
3. publicRedHeadDuck(){
4. flyBehavior=newFlyWithWings();//子类中改变实现，且互不影响。
5. quackBehavior=newQuack();
6. }
8. publicvoiddisplay(){
9. System.out.println("I'marealRedHeadedduck");
10. }
11. }

测试代码如下：

RedHeadDuck redHeadDuck = new RedHeadDuck();

redHeadDuck.performFly();
redHeadDuck.display();

输出结果：

I'm flying!!
I'm a real Red Headed duck

下面我们可以实现其他飞的方式，例如乘火箭

1. publicclassFlyRocketPoweredimplementsFlyBehavior{
2. publicvoidfly(){
3. System.out.println("I'mflyingwitharocket");
4. }
5. }

测试代码：

RedHeadDuck redHeadDuck = new RedHeadDuck();
redHeadDuck.setFlyBehavior(new FlyRocketPowered());
redHeadDuck.display();
redHeadDuck.performFly();

输出结果：

I'm a real Red Headed duck
I'm flying with a rocket

小结：

可见策略模式定义了算法，将他们分别封装，他们之间可以相互替换。（例如：FlyWithWings和FlyRocketPowered）

这样每个实现都相互不影响。