第四个设计模式：装饰模式

第四个设计模式：装饰模式

装饰模式是对对象功能增强时，平时使用继承的一种替代方案一．UML示意图：二．组成部分：1.?????? 抽象构件：原始的功能接口2.?????? 具体构件：具体的原始功能类3.?????? 装饰角色：持有具体构件类的对象，以便执行原有功能4.?????? 具体装饰：具体扩展的功能在这里三．例子代码:使用装饰模式来演示一个对”行走”功能扩展的例子(听音乐+行走和唱歌+行走)1．?抽象构件package com.eekq.decorator;?publicinterface Component {??? /**原始接口*/??? publicvoid go();}2．?具体构件package com.eekq.decorator;?publicclass ConcreteComponent implements Component {???? publicvoid go() {???? ??????? System.out.println("行走");??? }?}3．装饰角色来了package com.eekq.decorator;?publicclass Decorator implements Component {??? /**持有私有的原始构件*/??? private Component component;???? /**构造子，委派给原始构件*/??? protected Decorator(Component component) {??????? this.component = component;??? }???? /**调用原始构件功能，通常就可直接把扩展功能加在此方法中*/??? publicvoid go() {??????? this.component.go();??? }?}4．具体装饰（这里演示了两种扩展的情况，走路+听音乐和唱歌s）(1).package com.eekq.decorator;?publicclass ConcreteDecoratorListen extends Decorator {???? /**构造子，相关初始化*/??? public ConcreteDecoratorListen(Component component) {??????? super(component);??????? // code is here??? }???? /**商业逻辑，对原始构件功能的扩展*/??? publicvoid go() {???? ??????? listen("听音乐");//执行扩展功能??????? super.go();??? }??? ??? privatevoid listen(Object obj){??????? System.out.println(obj);??????? ??? }?}(2).package com.eekq.decorator;?publicclass ConcreteDecoratorSing extends Decorator {???? /**构造子，相关初始化*/??? public ConcreteDecoratorSing(Component component) {??????? super(component);??????? // code is here??? }???? /**商业逻辑，对原始构件功能的扩展*/??? publicvoid go() {???? ??????? super.go();??????? System.out.println(sing());;// 执行扩展功能??? }???? private String sing() {??????? return"唱歌";??? }}5．客户端调用package com.eekq.decorator;?publicclass Main {???? publicstaticvoid main(String[] args) {??????? /**原始构件*/??????? Component component = new ConcreteComponent();??????? /**边听音乐，边走路*/??????? ConcreteDecoratorListen cdl = new ConcreteDecoratorListen(component);??????? cdl.go();??????? System.out.println();??????? /**边走路，边唱歌*/??????? ConcreteDecoratorSing cds = new ConcreteDecoratorSing(component);??????? cds.go();??? }?}四．总结优点：装饰模式和继承都是对功能的扩展,而装饰模式使用的是组合,可以不用继承而达到这一效果.使用过多的继承会增加系统的复杂性和偶合性缺点：装饰模式要产生一些辅助性的对象,但这些对象看上去都比较像,不是很容易检查(好的命名应该是提高检查的一个办法)