Head First 策略模式

public interface FlyBehavior {
    public void fly();
}

public interface QuackBehavior {
    public void quack();
}

public class FlyNoWay implements FlyBehavior{
    public void fly() {
        System.out.println("I can‘t fly");
    }
}

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

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


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

public class MuteQuack implements QuackBehavior {
    public void quack() {
        System.out.println("<< Silence >>");
    }
}

public abstract class Duck {

    //为行为接口类型声明两个引用变量，所有的鸭子类都继承它们
    FlyBehavior flyBehavior;
    QuackBehavior quackBehavior;

    public Duck(){

    }

    public abstract void display();

    //委托给行为类
    public void performFly(){
        flyBehavior.fly();
    }
    public void performQuack(){
        quackBehavior.quack();
    }

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

    //动态设定行为
    public void setFlyBehavior(FlyBehavior fb){
        flyBehavior = fb;
    }
    public void setQuackBehavior(QuackBehavior qb){
        quackBehavior = qb;
    }

}

public class MallardDuck extends Duck {

    public MallardDuck(){
        //根据需求选择行为
        quackBehavior = new Quack();
        flyBehavior = new FlyWithWings();
    }

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

public class MinDuckSimulator {

    public static void main(String[] args){
        Duck mallard = new MallardDuck();
        mallard.performQuack();
        mallard.performFly();
    }

}