策略模式

策略模式定义了算法族，分别封装起来，让他们之间可以互相替换，此模式让算法的变化独立于实用算法的客户。

类图

java代码

// 飞行接口
public interface Fly {
    void fly();
}

// 不会飞
public class FlyCanNot implements Fly {
    @Override
    public void fly() {
        System.out.println("can not fly!!!");
    }
}

// 用火箭飞
public class FlyWithRocket implements Fly {
    @Override
    public void fly() {
        System.out.println("fly with rocket!!!");
    }
}

// 用翅膀飞
public class FlyWithWing implements Fly {
    @Override
    public void fly() {
        System.out.println("fly with wing!!!");
    }
}

// 游泳接口
public interface Swim {
    void swim();
}

// 不会游泳
public class SwimCanNot implements Swim {
    @Override
    public void swim() {
        System.out.println("can not swim!");
    }
}

// 用脚游泳
public class SwimWithFoot implements Swim {
    @Override
    public void swim() {
        System.out.println("swim with foot!");
    }
}

// 鸭子抽象类
public abstract class Duck {

    protected Fly fly;
    protected Swim swim;

    public abstract void show();

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

    public void swim() {
        swim.swim();
    }


    public void setFly(Fly fly) {
        this.fly = fly;
    }

    public void setSwim(Swim swim) {
        this.swim = swim;
    }
}

// 机械鸭
public class MachineDuck extends Duck {

    public MachineDuck() {
        fly = new FlyWithWing();
        swim = new SwimWithFoot();
    }

    @Override
    public void show() {
        System.out.println("i ~ am ~ machine ~ duck ~");
    }
}

// 模型鸭
public class ModelDuck extends Duck {

    public ModelDuck() {
        fly = new FlyCanNot();
        swim = new SwimCanNot();
    }

    @Override
    public void show() {
        System.out.println("i am model duck.");
    }
}

// 测试类
public class Test {

    public static void main(String[] args) {
        new Test().test();
    }

    private void test() {

        ModelDuck modelDuck = new ModelDuck();
        modelDuck.show();
        modelDuck.fly();
        modelDuck.swim();

        MachineDuck machineDuck = new MachineDuck();
        machineDuck.show();
        machineDuck.fly();
        machineDuck.swim();
        machineDuck.setFly(new FlyWithRocket());
        machineDuck.fly();

    }
}

注：

鸭子现在将飞行和呱呱叫的动作委托别人处理，而不是使用定义在Duck类中的呱呱叫和飞行方法。

参考文章
Head First 设计模式