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[Java教程]Java装饰者模式


Java装饰者模式简介

 一、假设有一个Worker接口,它有一个doSomething方法,Plumber和Carpenter都实现了Worker接口,代码及关系如下:

 

1.Worker.javapackage decorator;public interface Worker {  public void doSomething();}

 

2.Plumber.javapublic class Plumber implements Worker {  @Override  public void doSomething() {    System.out.println("修理水管");  }}

 

3.Carpenterpublic class Carpenter implements Worker{  public void doSomething(){    System.out.println("修门窗");  }}

4.测试代码 Test.javapublic class Test {  public static void main(String[] args) {    Worker worker = null;    Carpenter carpenter = new Carpenter();    Plumber plumber = new Plumber();    worker = carpenter;    worker.doSomething();    worker = plumber;    worker.doSomething();  }}

测试结果如下:

 

二、现有A、B两家公司,都有木工(Carpenter)和水管工(Plumber),但两公司的对两个工种的要求都不同,A公司要求员工在doSomething前自己介绍“我是A公司的”;B公司要求员工在doSomething前自己介绍“我是B公司的”;一个直接但不科学的设计方法是为每个公司都设计各自的木工(Carpenter)和水管工(Plumber),若公司增加到100个,则类要增加到200个,若再增加其他工种,则类会更多,关系如下:

 

三、此情况适合采用装饰者模式,为每个公司设计一个装饰类xWorker,xWorker也实现Worker接口,且有一个参数类型为Worker的构造函数和一个类型为Worker的成员变量,这样xWorker就可以取得相应类型worker的引用,在xWorker的doSomething()方法里处理各自公司的特殊要求:

 

 

 1 增加类 AWorker.java 2  3 public class AWorker implements Worker { 4  5   private Worker worker; 6    7   //通过些构造函数,AWorker就可以得到具体工种的引用, 8   //为下面的doSomething()方法中加入A公司的特殊要求做准备 9   public AWorker(Worker worker){10     this.worker = worker;11   }12   13   @Override14   public void doSomething() {15     System.out.println("您好!我是A公司的员工");16     worker.doSomething();17   }18 19 }

 

 1 //增加类 BWorker.java 2  3 public class BWorker implements Worker { 4  5   private Worker worker; 6    7   public BWorker(Worker worker){ 8     this.worker = worker; 9   }10   11   @Override12   public void doSomething() {13     System.out.println("您好!我是B公司的员工。");14     worker.doSomething();15   }16 17 }

 

 1 //测试代码 2    3 public static void main(String[] args) { 4      5     //A公司 6     Carpenter carpenterA = new Carpenter(); 7     Plumber plumberA = new Plumber(); 8     AWorker aWorker1 = new AWorker(carpenterA); 9     AWorker aWorker2 = new AWorker(plumberA);10     11     aWorker1.doSomething();12     aWorker2.doSomething();13   14     System.out.println("==================================");15     16     //B公司17     Carpenter carpenterB = new Carpenter();18     Plumber plumberB = new Plumber();19     BWorker bWorker1 = new BWorker(carpenterB);20     BWorker bWorker2 = new BWorker(plumberB);21     22     bWorker1.doSomething();23     bWorker2.doSomething();24   }25 }

测试结果: