结构型模式--装饰模式（Decorator）_JAVA_编程开发_程序员俱乐部

顾名思义，装饰模式就是给一个对象增加一些新的功能，而且是动态的，要求装饰对象和被装饰对象实现同一个接口，装饰对象持有被装饰对象的实例，关系图如下：

Source类是被装饰类，Decorator类是一个装饰类，可以为Source类动态的添加一些功能，代码如下：

1. public?interface?Sourceable?{??
2. ????public?void?method();??
3. }??

1. public?class?Source?implements?Sourceable?{??
2. ??
3. ????@Override??
4. ????public?void?method()?{??
5. ????????System.out.println("the?original?method!");??
6. ????}??
7. }??

1. public?class?Decorator?implements?Sourceable?{??
2. ??
3. ????private?Sourceable?source;??
4. ??????
5. ????public?Decorator(Sourceable?source){??
6. ????????super();??
7. ????????this.source?=?source;??
8. ????}??
9. ????@Override??
10. ????public?void?method()?{??
11. ????????System.out.println("before?decorator!");??
12. ????????source.method();??
13. ????????System.out.println("after?decorator!");??
14. ????}??
15. }??

测试类：

1. public?class?DecoratorTest?{??
2. ??
3. ????public?static?void?main(String[]?args)?{??
4. ????????Sourceable?source?=?new?Source();??
5. ????????Sourceable?obj?=?new?Decorator(source);??
6. ????????obj.method();??
7. ????}??
8. }??

输出：

before decorator!
the original method!
after decorator!

装饰器模式的应用场景：

1、需要扩展一个类的功能。

2、动态的为一个对象增加功能，而且还能动态撤销。（继承不能做到这一点，继承的功能是静态的，不能动态增删。）

缺点：产生过多相似的对象，不易排错！

?

==================================================================
?另外一个例子：

/** * Test.java 
* Created on 2013-8-1 上午10:02:29 
*/

package my;

/** 
 * <p>Project: Test2</p> 
 * <p>Title: Test.java</p> 
 * <p>Description: </p> 
 * <p>Copyright (c) 2013 Wilmar Consultancy Services</p>
 * <p>All Rights Reserved.</p>
 * @author <a href="mailto:liyong@wcs-global.com">liyong</a>
 */

public class Test {

	public static void main(String[] args) {

		Teacher t1 = new SimpleTeacher();

		Teacher t2 = new CppTeacher(t1);

		Teacher t3 = new JavaTeacher(t2);

		t3.teach();

		// t.teach();

	}

}

abstract class Teacher {

	public abstract void teach();

}

class SimpleTeacher extends Teacher {

	public void teach() {

		System.out.println("Good Good Study, Day Day Up");

	}

}

class JavaTeacher extends Teacher {

	Teacher teacher;

	public JavaTeacher(Teacher t) {

		this.teacher = t;
	}

	public void teach() {

		teacher.teach();

		System.out.println("Teach Java");

	}

}

class CppTeacher extends Teacher {

	Teacher teacher;

	public CppTeacher(Teacher t) {

		this.teacher = t;

	}

	public void teach() {

		teacher.teach();

		System.out.println("Teach C++");

	}

}

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