《设计模式(三)之——装饰者模式》

浅浅的花香味﹌ 2022-12-12 12:30 167阅读 0赞

#### 一、情景： ####

> **老王在卖的煎饼摊子开张了，主营产品有煎饼、鸡蛋、火腿。  
> 问题：1、有顾客想买加了鸡蛋的煎饼、或者加了火腿、鸡蛋的煎饼，那么该如何改造呢？**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczMjk1NQ_size_16_color_FFFFFF_t_70_pic_center]

#### 二、情景后续 ####

> **设计模式大佬、推荐他用装饰者模式，进行包装、包装出带有鸡蛋的煎饼**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczMjk1NQ_size_16_color_FFFFFF_t_70_pic_center 1]

#### 三、装饰者模式（Decorator） ####

*  **定义：动态的将责任附加到对象上若老扩展功能，装饰者提供老比继承更有弹性的替代方案**
 *  重要组件
 *  Component 被包装的原始组件
 *  Decorator 实现与原始组件相同的接口，并且组合了一个原始组件的引用

#### 四、代码演示 ####

##### 4.1类图 #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczMjk1NQ_size_16_color_FFFFFF_t_70_pic_center 2]

##### 4.2 煎饼、鸡蛋、火腿公共接口(Component) #####

/** * @author liuzihao * @create 2020-10-07-11:45 * 煎饼摊子基本接口 */
    public interface JbComponent { 
        /** * 描述 * @return */
        public String desc();
    
        /** * 价格 * @return */
        public BigDecimal price();
    }

##### 4.3 各自的实现(ConcreteComponent) #####

/** * @author liuzihao * @create 2020-10-07-11:48 * 鸡蛋 */
    public class JbComponenteEgg implements JbComponent { 
        @Override
        public String desc() { 
            return "鸡蛋";
        }
    
        @Override
        public BigDecimal price() { 
            return new BigDecimal("1");
        }
    }
    
    /** * @author liuzihao * @create 2020-10-07-11:47 */
    public class JbComponentPancakes implements  JbComponent{ 
        @Override
        public String desc() { 
            return "煎饼";
        }
    
        @Override
        public BigDecimal price() { 
            return new BigDecimal(2);
        }
    }
    /** * @author liuzihao * @create 2020-10-07-11:48 */
    public class JbComponenthHotDog implements JbComponent { 
        @Override
        public String desc() { 
            return "火腿";
        }
    
        @Override
        public BigDecimal price() { 
            return new BigDecimal(1);
        }
    }

##### 4.4 装饰者——带有鸡蛋煎饼(ConcreteDecoratoerA) #####

/** * @author liuzihao * @create 2020-10-07-11:51 */
    public class DecoratorPancakesWithEgg implements JbComponent { 
        private JbComponent jbComponent;
    
        public DecoratorPancakesWithEgg(JbComponent jbComponent) { 
            this.jbComponent = jbComponent;
        }
        @Override
        public String desc() { 
            return jbComponent.desc() + "\t" + "加鸡蛋";
        }
    
        @Override
        public BigDecimal price() { 
            return jbComponent.price().add(BigDecimal.ONE);
        }
    }

##### 4.5 装饰者——带有鸡蛋、火腿的煎饼(ConcreteDecoratoerB) #####

/** * @author liuzihao * @create 2020-10-07-11:54 */
    public class DecoratorPancakesWithHotDog implements JbComponent{ 
    	// 传入已经加了鸡蛋的煎饼
        private JbComponent jbComponent;
    
        public DecoratorPancakesWithHotDog(JbComponent jbComponent) { 
            this.jbComponent = jbComponent;
        }
        @Override
        public String desc() { 
            return jbComponent.desc() +"\t" + "加热狗";
        }
    
        @Override
        public BigDecimal price() { 
            return jbComponent.price().add(BigDecimal.ONE);
        }
    }

##### 4.6 代码测试 #####

public class DemoMain { 
        public static void main(String[] args) { 
            JbComponent jbComponent1 = new JbComponenthHotDog();
            System.out.println("卖" + jbComponent1.desc() + "\t 价格" +jbComponent1.price());
            JbComponent jbComponent2 = new JbComponenteEgg();
            System.out.println("卖" + jbComponent2.desc() + "\t 价格" +jbComponent2.price());
            JbComponent jbComponent3 = new JbComponentPancakes();
            System.out.println("卖" + jbComponent3.desc() + "\t 价格" +jbComponent3.price());
    
            System.out.println("==开始卖包装产品==");
            JbComponent jbComponent4 = new DecoratorPancakesWithEgg(jbComponent3);
            System.out.println("卖" + jbComponent4.desc() + "\t 价格" +jbComponent4.price());
            JbComponent jbComponent5 = new DecoratorPancakesWithEgg(jbComponent4);
            System.out.println("卖" + jbComponent5.desc() + "\t 价格" +jbComponent5.price());
    
    
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczMjk1NQ_size_16_color_FFFFFF_t_70_pic_center 3]

#### 五、小结 ####

##### 5.1改造之后的煎饼摊子 #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczMjk1NQ_size_16_color_FFFFFF_t_70_pic_center 4]

##### 5.2总结 #####

*  装饰者模式同继承一样，可以扩展行为，这符合开闭原则，但是有一个不好的地方就是这样会到账设计中出现很多小对象，程序的复杂性会增加。
 *  装饰者可以不断的叠加，例如上述案例中，可以用完包装完鸡蛋后，继续包装鸡蛋、不断重复包装行为。

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