The Strategy Pattern defines a family of algorithms,encapsulates each one, and makes them interchangeable.Strategy lets the algorithm vary independently fromclients that use it.

 

1.Duck 问题(head frist oop)

 

有的能飞，有的能叫，经典问题.

//Duck.javapublic abstract class Duck {FlyBehavior flyBehavior;QuackBehavior quackBehavior;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 class MallardDuck extends Duck {public MallardDuck() {quackBehavior = new Quack();flyBehavior = new FlyWithWings();}public void display() {System.out.println(“I’m a real Mallard duck”);}}

//Type and compile the FlyBehavior interface (FlyBehavior.java) and//the two behavior implementation classes (FlyWithWings.java and//FlyNoWay.java). 接口作为一个行为，因为有的能飞有的不能飞，所以不能够在父类里写fly(). 用一个interface作为一个行为汇总，interface下还有其他的行为.public interface FlyBehavior {public void fly();}

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public class FlyWithWings implements FlyBehavior {public void fly() {System.out.println(“I’m flying!!”);}}

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public class FlyNoWay implements FlyBehavior {public void fly() {System.out.println(“I can’t fly”);}}

 

public interface QuackBehavior {public void quack();}

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

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

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public class Squeak implements QuackBehavior {
   public void quack() {

System.out.println(“Squeak”);}}

Setting behavior dynamically

//Add two new methods to the Duck class:public void setFlyBehavior(FlyBehavior fb) {fl yBehavior = fb;}public void setQuackBehavior(QuackBehavior qb) {quackBehavior = qb;}

//Make a new Duck type (ModelDuck.java).public class ModelDuck extends Duck {public ModelDuck() {flyBehavior = new FlyNoWay();quackBehavior = new Quack();}public void display() {System.out.println(“I’m a model duck”);}}

//Make a new FlyBehavior type (FlyRocketPowered.java).public class FlyRocketPowered implements FlyBehavior {public void fly() {System.out.println(“I’m fl ying with a rocket!”);}}

//Change the test class (MiniDuckSimulator.java), add the//ModelDuck, and make the ModelDuck rocket-enabled.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();}}