策略模式定義了一系列的算法，並將每一個算法封裝起來，而且使它們可以相互替換，讓算法獨立於使用它的客戶而獨立變化，具體應用場景如第三方支付對接不同銀行的算法。

　　要點：1）抽象策略角色

　　　　 2）具體策略角色：包裝相關算法和行為

　　　　　3）環境角色：持有一個策略類的引用，最終給客戶端調用

1、抽象策略接口

public interface SwimmingStratege {
    public void swimming();
}

2、具體策略角色SwimmingWithFoot

public class SwimmingWithFoot implements SwimmingStratege {
    
 
public void swimming() {
        System.out.println("我借助腳滑動在水中遊走");
    }
}

3、具體策略角色SwimmingWithWind

public class SwimmingWithWind implements SwimmingStratege {
    public void swimming() {
        System.out.println("我借助風在水中遊走");
    }
}

4、環境角色Duck 抽象類

public abstract class Duck {

    public void
 
 quack() {
        System.out.println("嘎嘎嘎");
    }

    public abstract void display();

    private SwimmingStratege swimmingStratege;

    public void setSwimmingStratege(SwimmingStratege swimmingStratege) {
        this.swimmingStratege = swimmingStratege;
    }

    public void swimming() {
        swimmingStratege.swimming();
    }
}
 

5、環境角色RealDuck

public class RealDuck extends Duck {

    public RealDuck() {
        super();
        super.setSwimmingStratege(new SwimmingWithFoot());
    }

    @Override
    public void quack() {
        super.quack();
    }

    public void display() {
        System.out.println("我是真的鴨子");
    }
}

6、環境角色

public class YellowDuck extends Duck {

    public YellowDuck() {
        super();
        super.setSwimmingStratege(new SwimmingWithWind());
    }

    @Override
    public void quack() {
        super.quack();
    }

    public void display() {
        System.out.println("我是大黃鴨");
    }

}

7、測試

public class Model {

    public static void main(String[] args) {
        Duck duck = new RealDuck();
//        Duck duck = new YellowDuck();
        duck.display();
        duck.quack();
        duck.swimming();
    }

}

java設計模式（六）策略模式