再说装饰器模式

男娘i 2022-06-03 05:28 68阅读 0赞

> To extend or modify the behaviour of **an instance** at runtime decorator design pattern is used. Inheritance is used to extend the abilities of **a class**. Unlike inheritance, you can choose any single object of a class and modify its behaviour leaving the other instances unmodified.

这是我们生活中一种常见的美味，其制作过程就是一种典型的装饰器模式，除了原味，我们可以额外添加坚果、草莓等额外的美味，同时还保持了原有冰淇淋的美味。

![这里写图片描述][SouthEast]

装饰器模式的UML类图

![这里写图片描述][SouthEast 1]

*  定义冰淇淋制作接口**Icecream**

public interface Icecream {
        String makeIcecream();
    }

*  原味冰淇淋：SimpleIcecream

public class SimpleIcecream implements Icecream { 
    
      @Override
      public String makeIcecream() {
        return "Base Icecream";
      }
    
    }

*  冰淇淋装饰器抽象类

abstract public class IcecreamDecorator implements Icecream { 
        protected Icecream specialIcecream;
    
        public IcecreamDecorator(Icecream specialIcecream) {
            this.specialIcecream = specialIcecream;
        }
    
        public String makeIcecream() {
            return specialIcecream.makeIcecream();
        }
    
    }

*  坚果冰淇淋装饰

public class NuttyDecorator extends IcecreamDecorator { 
        public NuttyDecorator(Icecream specialIcecream) {
            super(specialIcecream);
        }
    
        public String makeIcecream() {
            System.out.println("NuttyDecorator makeIcecream");
            return specialIcecream.makeIcecream() + addNuts();
        }
    
        private String addNuts() {
            return " + cruncy nuts";
        }
    }

*  草莓冰淇淋装饰

public class StrawberryDecorator extends IcecreamDecorator { 
        public StrawberryDecorator(Icecream specialIcecream) {
            super(specialIcecream);
        }
    
        public String makeIcecream() {
            System.out.println("StrawberryDecorator makeIcecream");
            return super.makeIcecream() + " + strawberry";
        }
    }

*  可爱甜心冰淇淋装饰

public class HoneyDecorator extends IcecreamDecorator { 
    
        public HoneyDecorator(Icecream specialIcecream) {
            super(specialIcecream);
        }
    
        public String makeIcecream() {
            System.out.println("HoneyDecorator makeIcecream");
            return specialIcecream.makeIcecream() + addHoney();
        }
    
        private String addHoney() {
            return " + sweet honey";
        }
    }

*  最后我们来制作一个多味的冰淇淋，同时添加了坚果、草莓与可爱甜心

public class TestDecorator {
        public static void main(String args[]) {
    
            Icecream icecream = new StrawberryDecorator(new HoneyDecorator(new NuttyDecorator(new SimpleIcecream())));
            System.out.println(icecream.makeIcecream());
    
        }
    }

[https://javapapers.com/design-patterns/decorator-pattern/][https_javapapers.com_design-patterns_decorator-pattern]

[SouthEast]: /images/20220603/238e8bf7fefe4fc0ad8e66348e7d8f00.png
[SouthEast 1]: /images/20220603/b02185c2cf7e4b6ba63f69c0c133a29a.png
[https_javapapers.com_design-patterns_decorator-pattern]: https://javapapers.com/design-patterns/decorator-pattern/