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：