Java-马士兵设计模式学习笔记-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.java
package decorator;

public interface Worker {
    public void doSomething();
}

2.Plumber.java

public class Plumber implements Worker {

    @Override
    public void doSomething() {
        System.out.println("修理水管");
    }

}

3.Carpenter

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

4.测试代码 Test.java

public 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：

 增加类 AWorker.java

 public class AWorker implements Worker {

     private Worker worker;

     //通过些构造函数，AWorker就可以得到具体工种的引用，
     //为下面的doSomething()方法中加入A公司的特殊要求做准备
     public AWorker(Worker worker){
         this.worker = worker;
     }

     @Override
     public void doSomething() {
         System.out.println("您好！我是A公司的员工");
         worker.doSomething();
     }

 }

 //增加类 BWorker.java

 public class BWorker implements Worker {

     private Worker worker;

     public BWorker(Worker worker){
         this.worker = worker;
     }

     @Override
     public void doSomething() {
         System.out.println("您好！我是B公司的员工。");
         worker.doSomething();
     }

 }

 //测试代码

 public static void main(String[] args) {

         //A公司
         Carpenter carpenterA = new Carpenter();
         Plumber plumberA = new Plumber();
         AWorker aWorker1 = new AWorker(carpenterA);
         AWorker aWorker2 = new AWorker(plumberA);

         aWorker1.doSomething();
         aWorker2.doSomething();

         System.out.println("==================================");

         //B公司
         Carpenter carpenterB = new Carpenter();
         Plumber plumberB = new Plumber();
         BWorker bWorker1 = new BWorker(carpenterB);
         BWorker bWorker2 = new BWorker(plumberB);

         bWorker1.doSomething();
         bWorker2.doSomething();
     }
 }

测试结果：