装饰者模式——Head First Design Patterns

最新推荐文章于 2020-04-08 23:26:53 发布

peking1987

最新推荐文章于 2020-04-08 23:26:53 发布

阅读量440

点赞数

分类专栏：读书笔记

读书笔记专栏收录该内容

27 篇文章

订阅专栏

本文介绍了一种灵活的功能扩展方法——装饰者模式，它允许在运行时为已有对象添加额外功能，通过实例化扩展类来实现动态功能增强。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

定义：提供一种比扩展更灵活的选择（实际上还是用了组合），给对象动态地添加额外的功能。

使用场景： 当需要给已有功能添加额外的功能时

类图：

代码样例：JDK内置的输入流代码（如PushbackInputStream）

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

public abstract class Beverage {
	String description = "Unknown Beverage";
  
	public String getDescription() {
		return description;
	}
 
	public abstract double cost();
}

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

public class Milk extends CondimentDecorator {
	Beverage beverage;

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

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

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

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();
	}
}

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();
	}
}

优点：1）能够在运行时动态的给已有对象添加一些额外的功能；

缺点：1）增加了代码的复杂性

类似的设计模式：

配套的内功心法：1）类应该开放扩展功能，关闭修改功能（Open-Closed Principle），当然这个原则应该慎用，到处都使用会导致代码变得很复杂，可读性变差；