装饰模式Decorator

1. 定义
动态地给一个对象添加一些额外的职责。就增加功能来说，装饰模式比生成子类更为灵活。

 

2. 结构图

Component：组件对象的接口，可以给这些对象动态地添加职责。
ConcreteComponent：具体的组件对象，实现组件对象接口，通常就是被装饰器装饰的原始对象，也就是可以给这个对象添加职责。
Decorator：所有装饰器的抽象父类，需要定义一个与组件接口一致的接口，并持有一个Component对象，其实就是持有一个被装饰的对象。注意这个被装饰的对象不一定是最原始的那个对象，也可能是被其他装饰器装饰过后的对象，反正都是实现的同一个接口，也就是同一类型。
ConcreteDecorator：实际的装饰器对象，实现具体要向被装饰器对象添加的功能。

 

3. 本质
装饰模式的本质：动态组合。

 

4. Code Demo

Component.java

package org.fool.decorator;

public interface Component {
	public void doSomething();
}

 

ConcreteComponent.java

package org.fool.decorator;

public class ConcreteComponent implements Component {
	@Override
	public void doSomething() {
		System.out.println("功能A");
	}

}

 

Decorator.java

package org.fool.decorator;

public class Decorator implements Component {
	private Component component;

	public Decorator(Component component) {
		this.component = component;
	}

	@Override
	public void doSomething() {
		component.doSomething();
	}
}

 

ConcreteDecorator1.java

package org.fool.decorator;

public class ConcreteDecorator1 extends Decorator {
	public ConcreteDecorator1(Component component) {
		super(component);
	}

	@Override
	public void doSomething() {
		super.doSomething();

		this.doAnotherThing();
	}

	private void doAnotherThing() {
		System.out.println("功能B");
	}

}

 

ConcreteDecorator2.java

package org.fool.decorator;

public class ConcreteDecorator2 extends Decorator {
	public ConcreteDecorator2(Component component) {
		super(component);
	}

	@Override
	public void doSomething() {
		super.doSomething();

		this.doAnotherThing();
	}

	private void doAnotherThing() {
		System.out.println("功能C");
	}
}

 

Client.java

package org.fool.decorator;

public class Client {
	public static void main(String[] args) {
		/*
		 * //节点流 Component component = new ConcreteComponent();
		 * 
		 * //过滤流 Component component2 = new ConcreteDecorator1(component);
		 * 
		 * component2.doSomething();
		 * 
		 * System.out.println("------------");
		 * 
		 * //过滤流 Component component3 = new ConcreteDecorator2(component2);
		 * 
		 * component3.doSomething();
		 */

		Component component = new ConcreteDecorator1(new ConcreteDecorator2(new ConcreteComponent()));

		component.doSomething();
	}
}