layout: post
title: "Design Patterns"
category:
tags: [“Java”, "设计模式"]
{% include JB/setup %}
Adapter
保持系统的多态性。让第三方接口符合系统已定义的的接口。
你把数据给我，我来带你转给第三方办，你不要关心我是怎么办到的，你不关心我找谁办的，反正肯定给你办成。
我的系统里已经实现了点、线、正方形，现在客户要求我们实现一个圆形
我们会建立一个Circle类来继承Shape，然后需要去实现display、fill、undisplay方法
但是这时我发现同事已经实现了一个画圆的类，但是他的方法名为displayIt、fillIt、undisplayIt
我们不能直接使用这个类，因为那样无法保持多态性，
class Circle extends Shape
{
private XXCircle pxc;
public Circle()
{
pxc = new XXCircle();
}
public void display()
{
pxc.displayIt();
}
}
Abstract Factory
public interface Creator
{
public ProductA factoryA();
public ProductB factoryB();
}
具体工厂类1：
public class ConcreteCreator1 implements Creator
{
public ProductA factoryA()
{
return new ProductA1();
}
public ProductB factoryB()
{
return new ProductB1();
}
}
具体工厂类2：
public class ConcreteCreator2 implements Creator
{
public ProductA factoryA()
{
return new ProductA2();
}
public ProductB factoryB()
{
return new ProductB2();
}
}
Factory--->UnixFactory/WinFactory
Button--->UnixButton/WinButton
Text----->UnixText/WinText
Unix产品族和Windows产品族，不会同时使用。
//两种抽象产品：水果、蔬菜
public interface Fruit
{
}
public interface Veggie
{
}
//四种具体产品：北方水果，热带水果，北方蔬菜，热带蔬菜
//Northern Fruit
public class NorthernFruit implements Fruit
{
private String name;
public NorthernFruit(String name)
{
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
}
//TropicalFruit
public class TropicalFruit implements Fruit
{
private String name;
public TropicalFruit(String name)
{
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
}
//NorthernVeggie
public class NorthernVeggie implements Veggie
{
private String name;
public NorthernVeggie(String name)
{
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
}
//TropicalVeggie
public class TropicalVeggie implements Veggie
{
private String name;
public TropicalVeggie(String name)
{
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
}
//抽象工厂角色
public interface Gardener
{
public Fruit createFruit(String name);
public Veggie createVeggie(String name);
}
//具体工厂角色：北方工厂，热带角色
public class NorthernGardener implements Gardener
{
public Fruit createFruit(String name)
{
return new NorthernFruit(name);
}
public Veggie createVeggie(String name)
{
return new NorthernVeggie(name);
}
}
public class TropicalGardener implements Gardener
{
public Fruit createFruit(String name)
{
return new TropicalFruit(name);
}
public Veggie createVeggie(String name)
{
return new TropicalVeggie(name);
}
}
Facade
Decorator
要点喝的，有奶茶，咖啡，茶。另外每一种饮品还能加上珍珠，糖，布丁之类的料。
最后我点：奶茶加珍珠加布丁。
public abstract class Beverage
{
String description = "Unknow Beverage";
public String getDescription()
{
return description;
}
public abstract double cost();
}
public abstract class CondimentDecorator extends Beverage
{
public abstract String getDescription();
}
public class Espresso extends Beverage
{
public Espresso()
{
description = "Espresso";
}
public double cost()
{
return 1.99;
}
}
public class Mocha extends CondimentDecorator
{
Beverage beverage;
public Mocha(Beverage beverage)
{
this.beverage = beverage;
}
public String getDescription
{
return beverage.getDescription + ", Mocha";
}
public double cost()
{
return .2 + beverage.cost();
}
}
public class Whip extends CondimentDecorator
{
Beverage beverage;
public Mocha(Beverage beverage)
{
this.beverage = beverage;
}
public String getDescription
{
return beverage.getDescription + ", Whip";
}
public double cost()
{
return .9 + beverage.cost();
}
}
public class StarbuzzCoffee
{
public static void main(String args[])
{
Beverage beverage = new Espresso();
beverage = new Mocha(beverage);
beverage = new Mocha(beverage);
beverage = new Whip(beverage);
System.out.println(beverage.getDescription + " $"
+ beverage.cost());
}
}
Singleton
Observer
Observer更多的体现的是订阅与发布的思想
举个例子说明，Bea论坛上都会定期发布一些举办活动的通告，而想参加活动的都需要先去注册一下，然后报名
报名后，Bea会给所有的参加者发一封通知信，告诉又有人参加了
当然了，如果你取消注册，那么到时候将收不到通知了。
public interface BeaNotice
{
public void addObserver(Observer o);
public void removeObserver(Observer o);
public void addUser();
}
public class BeaNoticeImpl implements BeaNotice
{
private List observers = new ArrayList();
public void addObserver(Observer o){
observers.add(o);
}
public void removeObserver(Observer o){
observers.remove(o);
}
public void notifyAllObservers(){
for(int i = 0; i < observers.size(); i++){
((Observer)observers.get(i)).update(this);
}
}
public void addUser(){
//数据库操作，向数据库插入一个用户的信息，然后通知所有注册的用户
notifyAllObservers();
}
}
public interface Observer
{
public void update(BeaNoticeImpl bns);
}
public class WelcomeLetterObserver implements Observer
{
BeaNotice beaNotice = null;
public WelcomeLetterObserver(BeaNotice beaNotice){
this.beaNotice = beaNotice;
beaNotice.addObserver(this);
}
public void update(BeaNoticeImpl bns) {
System.out.println("This is a welocme letter!");
}
}
public class OtherNoticeObserver implements Observer
{
BeaNotice beaNotice = null;
public OtherNoticeObserver(BeaNotice beaNotice){
this.beaNotice = beaNotice;
beaNotice.addObserver(this);
}
public void update(BeaNoticeImpl bns) {
System.out.println("there is other Notice!");
}
}
Strategy
Proxy
有两个同学B和C，B是男的，C是女的，你晚上想给女同学C打电话咨询点事，
但是你女友不让所以，你只能通过你的男同学B和C通话，
然后把让B把反馈的结果告诉你
public interface IStudent
{
public String answerSomeQuestion();
}
public class IGirlImpl implements IStudent
{
public String answerSomeQuestion()
{
System.out.println("answer some question");
return "this is my answer";
}
}
public class IBoyProxyImpl implements IStudent
{
IGirlImpl girl = null;
public String answerSomeQuestion()
{
System.out.println("do someting before method invoke");
if(girl == null)
{
girl = new IGirlImpl();
}
String returnValue = girl.answerSomeQuestion();
System.out.println("do someting after method invoke");
return returnValue;
}
}
Reference
设计模式之Adapter模式, http://lizwjiang.iteye.com/blog/86391