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