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Java：设计模式之结构型-装饰者模式(decorator pattern)

web 2025/7/5 16:15:23

装饰者模式(decorator pattern): 动态地将责任附加到对象上

意图：为对象动态添加功能

类图
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实现

设计不同种类的饮料，饮料可以添加配料，比如可以添加牛奶，并且支持动态添加新配料。每增加一种配料，该饮料的价格就会增加，要求计算一种饮料的价格。
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项目结构

$ tree
.
├── Beverage.java                       # 接口
├── Client.java                         # 客户端调用方
└── impl├── CondimentDecorator.java         # 装饰器抽象类├── DarkRoast.java                  # Beverage的实现类├── HouseBlend.java                 # Beverage的实现类├── Milk.java                       # 装饰器抽象类的实现类└── Mocha.java                      # 装饰器抽象类的实现类

具体代码

public interface Beverage {double cost();
}

public class DarkRoast implements Beverage {@Overridepublic double cost() {return 1;}
}

public class HouseBlend implements Beverage {@Overridepublic double cost() {return 1;}
}

public abstract class CondimentDecorator implements Beverage {protected Beverage beverage;
}

public class Milk extends CondimentDecorator {public Milk(Beverage beverage) {this.beverage = beverage;}@Overridepublic double cost() {return 1 + beverage.cost();}
}

public class Mocha extends CondimentDecorator {public Mocha(Beverage beverage) {this.beverage = beverage;}@Overridepublic double cost() {return 1 + beverage.cost();}
}

public class Client {public static void main(String[] args) {Beverage beverage = new HouseBlend();beverage = new Mocha(beverage);beverage = new Milk(beverage);System.out.println(beverage.cost());// 3.0}
}