策略模式（strategy pattern）

下面的例子是运用多态的一个例子

package com.interfaces;

public interface FlyBehavior {

	public void fly();
}

package com.interfaces;

public interface QuackBehavior {

	public void quack();
}

package com.interfaces.impl;

import com.interfaces.FlyBehavior;

public class FlyNoWay implements FlyBehavior {

	@Override
	public void fly() {
		System.out.println("I can't fly");
	}
}

package com.interfaces.impl;

import com.interfaces.FlyBehavior;

public class FlyRocketPowered implements FlyBehavior {

	@Override
	public void fly() {
		System.out.println("I'm flying with a rocket!");
	}
}

package com.interfaces.impl;

import com.interfaces.FlyBehavior;

public class FlyWithWings implements FlyBehavior {

	@Override
	public void fly() {
		System.out.println("I'm flying");
	}
}

package com.interfaces.impl;

import com.interfaces.QuackBehavior;

public class MuteQuack implements QuackBehavior {

	@Override
	public void quack() {
		System.out.println("<<Silence>>");
	}
}

package com.interfaces.impl;

import com.interfaces.QuackBehavior;

public class Quack implements QuackBehavior {

	@Override
	public void quack() {
		System.out.println("Quack");
	}
}

package com.interfaces.impl;

import com.interfaces.QuackBehavior;

public class Squeak implements QuackBehavior {

	@Override
	public void quack() {
		System.out.println("Squeak");
	}
}

package com.bean;

import com.interfaces.FlyBehavior;
import com.interfaces.QuackBehavior;

public abstract class Duck {

	FlyBehavior flyBehavior;

	QuackBehavior quackBehavior;
	
	public FlyBehavior getFlyBehavior() {
		return flyBehavior;
	}

	public void setFlyBehavior(FlyBehavior flyBehavior) {
		this.flyBehavior = flyBehavior;
	}

	public QuackBehavior getQuackBehavior() {
		return quackBehavior;
	}

	public void setQuackBehavior(QuackBehavior quackBehavior) {
		this.quackBehavior = quackBehavior;
	}

	public abstract void display();

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

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

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

}

package com.bean;

import com.interfaces.impl.FlyWithWings;
import com.interfaces.impl.Quack;

public class MallardDuck extends Duck {

	
	public MallardDuck(){
		quackBehavior = new Quack();
		flyBehavior = new FlyWithWings();
	}
	
	@Override
	public void display() {
      System.out.println("I'm a real Mallard duck");
	}
}

package com.bean;

import com.interfaces.impl.FlyNoWay;
import com.interfaces.impl.Quack;

public class ModelDuck extends Duck {

	public ModelDuck(){
		flyBehavior = new FlyNoWay();
		quackBehavior = new Quack();
	}

	@Override
	public void display() {
		System.out.println("I'm a model duck");
	}
}

package com.test;

import com.bean.Duck;
import com.bean.MallardDuck;
import com.bean.ModelDuck;
import com.interfaces.impl.FlyRocketPowered;

public class MiniDuckSimulator {
	public static void main(String[] args) {
		Duck mallard = new MallardDuck();
		mallard.performFly();
		mallard.performQuack();
		
		Duck model = new ModelDuck();
		model.performFly();
		model.setFlyBehavior(new FlyRocketPowered());
		model.performFly();
	}
}

输出结果为：

I'm flying
Quack
I can't fly
I'm flying with a rocket!