讀書筆記1：Head First設計模式——策略模式

設計原則：

 1. 找出應用中可能需要變化之處，把它們獨立出來，不要和那些不需要變化的代碼混在一起

 2. 針對介面編程，而不是針對試下編程

 3. 多用組合，少用繼承

 策略模式：

             定義了演算法族，分別封裝起來，讓它們之間可以相互替換，此模式讓演算法的變化獨立於使用演算法的客戶。

Duck問題:

public abstract class Duck {QuackBehavior quackBehavior;FlyBehavior flyBehavior;//more...public Duck() {}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!");}public void setFlyBehavior(FlyBehavior fb){flyBehavior = fb;}public void setQuackBehavior(QuackBehavior qb){quackBehavior = qb;}}

public interface FlyBehavior {public void fly();}

public interface QuackBehavior {public void quack();}

public class FlyWitheWings implements FlyBehavior {@Overridepublic void fly() {// TODO Auto-generated method stubSystem.out.println("I am flying!!");}}

public class FlyNoWay implements FlyBehavior {@Overridepublic void fly() {// TODO Auto-generated method stubSystem.out.println("I cannot fly...");}}

public class FlyRocketPowered implements FlyBehavior {@Overridepublic void fly() {System.out.println("I am flying with a rocket!");}}

public class Quack implements QuackBehavior {@Overridepublic void quack() {// TODO Auto-generated method stubSystem.out.println("Quack");}}

public class MuteQuack implements QuackBehavior {@Overridepublic void quack() {// TODO Auto-generated method stubSystem.out.println("<<Silence>>");}}

public class Squeek implements QuackBehavior {@Overridepublic void quack() {// TODO Auto-generated method stubSystem.out.println("Squeak");}}

public class MallardDuck extends Duck{public MallardDuck(){quackBehavior = new Quack();flyBehavior = new FlyWitheWings();}@Overridepublic void display() {// TODO Auto-generated method stub}}

public class ModelDuck extends Duck {public ModelDuck() {flyBehavior = new FlyNoWay();quackBehavior = new Quack();}@Overridepublic void display() {System.out.println("I am a model duck");}}

//測試類別

public class MiniDuckSimulator {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();}}

輸出：

Quack
I am flying!!
I cannot fly...
I am flying with a rocket!