HeadFirst设计模式之策略模式

什么是策略模式：它定义了一系列算法，可以根据不同的实现调用不同的算法

大多数的设计模式都是为了解决系统中变化部分的问题

一、OO基础

抽象、封装、多态、继承

二、OO原则

1.封装变化，如把FlyBehavious、QuackBehavior从Duck中抽离出来

2.组合优于继承

3.面向抽象(接口、抽象类)编程而不是面向实现

4.为对象的解耦设计而努力

5.类应该对扩展开放，对修改封闭

6.依赖抽象，不要依赖具体

7.Principle of Least Knowledge -talk only to your immediate friends.

8.A class should have only one reason to change.

三、设计过程

1.不合理地用继承

2.需求变化，要增加飞行

3.继承的弊端出现，不需要的也会被继承

4.用接口也不合适

5.封装变化部分

6.策略模式，使不同的子类可以重用行为，且可以随时添加新行为而不影响现有代码

7.

四、代码实现

1.

 package headfirst.designpatterns.strategy;

 public abstract class Duck {
     FlyBehavior flyBehavior;
     QuackBehavior quackBehavior;

     public Duck() {
     }

     public void setFlyBehavior(FlyBehavior fb) {
         flyBehavior = fb;
     }

     public void setQuackBehavior(QuackBehavior qb) {
         quackBehavior = qb;
     }

     abstract void display();

     public void performFly() {
         flyBehavior.fly();
     }

     public void performQuack() {
         quackBehavior.quack();
     }

     public void swim() {
         System.out.println("All ducks float, even decoys!");
     }
 }

2.

package headfirst.designpatterns.strategy;

public interface FlyBehavior {
    public void fly();
}

3.

package headfirst.designpatterns.strategy;

public interface QuackBehavior {
    public void quack();
}

4.

 package headfirst.designpatterns.strategy;

 public class MallardDuck extends Duck {

     public MallardDuck() {

         quackBehavior = new Quack();
         flyBehavior = new FlyWithWings();

     }

     public void display() {
         System.out.println("I'm a real Mallard duck");
     }
 }

5.

package headfirst.designpatterns.strategy;

public class RedHeadDuck extends Duck {

    public RedHeadDuck() {
        flyBehavior = new FlyWithWings();
        quackBehavior = new Quack();
    }

    public void display() {
        System.out.println("I'm a real Red Headed duck");
    }
}

6.

package headfirst.designpatterns.strategy;

public class FlyWithWings implements FlyBehavior {
    public void fly() {
        System.out.println("I'm flying!!");
    }
}

7.

 package headfirst.designpatterns.strategy;

 public class FlyRocketPowered implements FlyBehavior {
     public void fly() {
         System.out.println("I'm flying with a rocket");
     }
 }

8.

package headfirst.designpatterns.strategy;

public class Quack implements QuackBehavior {
    public void quack() {
        System.out.println("Quack");
    }
}

9.

 package headfirst.designpatterns.strategy;

 public class Squeak implements QuackBehavior {
     public void quack() {
         System.out.println("Squeak");
     }
 }

10.

 package headfirst.designpatterns.strategy;

 public class MiniDuckSimulator {

     public static void main(String[] args) {

         MallardDuck    mallard = new MallardDuck();
         RubberDuck    rubberDuckie = new RubberDuck();
         DecoyDuck    decoy = new DecoyDuck();

         Duck     model = new ModelDuck();

         mallard.performQuack();
         rubberDuckie.performQuack();
         decoy.performQuack();

         model.performFly();
         model.setFlyBehavior(new FlyRocketPowered());
         model.performFly();
     }
 }

11.

 package headfirst.designpatterns.strategy;

 public class MiniDuckSimulator1 {

     public static void main(String[] args) {

         Duck mallard = new MallardDuck();
         mallard.performQuack();
         mallard.performFly();

         Duck model = new ModelDuck();
         model.performFly();
         model.setFlyBehavior(new FlyRocketPowered());
         model.performFly();

     }
 }

五.练习：在游戏中如何给不同角色赋予不同的武器