设计模式——装饰者模式

装饰者模式：

 

首先定义抽象的组件类，子类继承该类后持有抽象类的引用，在抽象类的基础上可以在调用父类方法前后分别执行自己的行为。从而实现装饰添加新的功能特性。再次强调了使用组合的好处。

强调对扩展开放，对修改关闭。

在Java I/O中应用了装饰者模式。

 

装饰者模式类图：

 

 

以下程序来自Head First设计模式中的实例代码，模拟了不同种类的饮料不同的售价计算方法。

 

1.定义饮料接口

 

package net.dp.decorator;

public abstract class Beverage {
	protected String description = "Unknown Beverage";

	public String getDescription() {
		return description;
	}

	public abstract double cost();
}

2.实现三种不同种类的饮料　　

package net.dp.decorator.coffee;

import net.dp.decorator.Beverage;

public class Espresso extends Beverage {

	public Espresso() {
		description = "Espresso";
	}

	public double cost() {
		return 1.99;
	}
}

　　

package net.dp.decorator;

public abstract class Beverage {
	protected String description = "Unknown Beverage";

	public String getDescription() {
		return description;
	}

	public abstract double cost();
}

　

package net.dp.decorator.coffee;

import net.dp.decorator.Beverage;

public class HouseBlend extends Beverage {

	public HouseBlend() {
		description = "House Blend Coffee";
	}

	public double cost() {
		return .89;
	}
}

　　

3.定义添加了调料的饮料抽象类

package net.dp.decorator;

public abstract class CondimentDecorator extends Beverage {
	public abstract String getDescription();
}

　　

4.实现不同调料的饮料

package net.dp.decorator.flovoring;

import net.dp.decorator.Beverage;
import net.dp.decorator.CondimentDecorator;

public class Mocha extends CondimentDecorator {
	Beverage beverage;

	public Mocha(Beverage beverage) {
		this.beverage = beverage;
	}

	public String getDescription() {
		return beverage.getDescription() + ", Mocha";
	}

	public double cost() {
		return .20 + beverage.cost();
	}
}

　　

package net.dp.decorator.flovoring;

import net.dp.decorator.Beverage;
import net.dp.decorator.CondimentDecorator;

public class Soy extends CondimentDecorator {
	Beverage beverage;

	public Soy(Beverage beverage) {
		this.beverage = beverage;
	}

	public String getDescription() {
		return beverage.getDescription() + ", Soy";
	}

	public double cost() {
		return .15 + beverage.cost();
	}
}

　　

package net.dp.decorator.flovoring;

import net.dp.decorator.Beverage;
import net.dp.decorator.CondimentDecorator;

public class Whip extends CondimentDecorator {
	Beverage beverage;

	public Whip(Beverage beverage) {
		this.beverage = beverage;
	}

	public String getDescription() {
		return beverage.getDescription() + ", Whip";
	}

	public double cost() {
		return .10 + beverage.cost();
	}
}

　　

5.终于大功告成！跑一把！

package net.dp.decorator;

import net.dp.decorator.coffee.DarkRoast;
import net.dp.decorator.coffee.Espresso;
import net.dp.decorator.coffee.HouseBlend;
import net.dp.decorator.flovoring.Mocha;
import net.dp.decorator.flovoring.Soy;
import net.dp.decorator.flovoring.Whip;

public class StarbuzzCoffee {

	public static void main(String[] args) {
		Beverage beverage = new Espresso();
		System.out.println(beverage.getDescription() + " $" + beverage.cost());

		Beverage beverage2 = new DarkRoast();
		beverage2 = new Mocha(beverage2);
		beverage2 = new Mocha(beverage2);
		beverage2 = new Whip(beverage2);
		System.out
				.println(beverage2.getDescription() + " $" + beverage2.cost());

		Beverage beverage3 = new HouseBlend();
		beverage3 = new Soy(beverage2);
		beverage3 = new Mocha(beverage2);
		beverage3 = new Whip(beverage2);
		System.out
				.println(beverage3.getDescription() + " $" + beverage3.cost());
	}
}

可以看到不同种类的饮料得出了不同的价格。