装饰者模式学习心得

Love The Way You Lie 2022-10-20 01:30 110阅读 0赞

# 装饰者模式定义 #

装饰者模式（Decorator Pattern）是指在不改变原有对象的基础之上，将功能附加到对象上，提供了比继承更有弹性的替代方案（扩展原有对象的功能），属于结构型模式。装饰者模式在我们生活中应用也比较多比如煎饼加鸡蛋加香肠。  
装饰者在代码程序中适用于以下场景：  
1，用于扩展一个类的功能或给一个类添加附加职责。  
2，动态的给一个对象添加功能，这些功能可以再动态的撤销。

# 下面我们以一个煎饼的例子 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zMDQwOTkyNw_size_16_color_FFFFFF_t_70]

## 创建一个建煎饼的抽象 Battercake 类 ##

package com.evan.spring.design.decorator;
    
    /** * @author evanYang * @version 1.0 * @date 2021/7/12 16:55 */
    public abstract class Battercake { 
    
        protected abstract String getMsg();
    
        protected abstract int getPrice();
    }

## 基本的煎饼（或者叫基础套餐）BaseBattercake ##

package com.evan.spring.design.decorator;
    
    /** * @author evanYang * @version 1.0 * @date 2021/7/12 17:00 */
    public class BaseBattercake extends Battercake{ 
        @Override
        protected String getMsg() { 
            return "煎饼";
        }
    
        @Override
        public int getPrice() { 
            return 5;
        }
    }

## 再创建一个扩展套餐的抽象装饰类BatterCakeDecotator类 ##

package com.evan.spring.design.decorator;
    
    /** * @author evanYang * @version 1.0 * @date 2021/7/12 17:03 */
    public abstract class BattercakeDectator extends Battercake{ 
        // 静态代理、委派
        private Battercake battercake;
    
        protected abstract void doSomething();
    
        public BattercakeDectator(Battercake battercake) { 
            this.battercake=battercake;
        }
    
        @Override
        protected String getMsg() { 
            return this.battercake.getMsg();
        }
    
        @Override
        protected int getPrice() { 
            return this.battercake.getPrice();
        }
    }

## 鸡蛋装饰者类 ##

package com.evan.spring.design.decorator;
    
    /** * @author evanYang * @version 1.0 * @date 2021/7/12 17:19 */
    public class EggDecorator extends BattercakeDectator{ 
        public EggDecorator(Battercake battercake) { 
            super(battercake);
        }
    
        @Override
        protected void doSomething() { 
    
        }
    
        @Override
        protected String getMsg(){ 
            return super.getMsg()+"加一个鸡蛋";
        }
    
        @Override
        protected int getPrice(){ 
            return super.getPrice()+1;
        }
    }

## 香肠装饰者类 ##

package com.evan.spring.design.decorator;
    
    import org.jcp.xml.dsig.internal.dom.DOMTransform;
    
    /** * @author evanYang * @version 1.0 * @date 2021/7/12 17:23 */
    public class SausageDecorator extends BattercakeDectator{ 
        public SausageDecorator(Battercake battercake) { 
            super(battercake);
        }
    
        @Override
        protected void doSomething() { 
    
        }
    
        @Override
        protected String getMsg(){ 
            return super.getMsg()+"+1根香肠";
        }
    
        @Override
        protected int getPrice(){ 
            return super.getPrice()+2;
        }
    }

## 测试代码 ##

package com.evan.spring.design.decorator;
    
    /** * @author evanYang * @version 1.0 * @date 2021/7/12 17:44 */
    public class BattercakeTest { 
        public static void main(String[] args) { 
            Battercake battercake;
            //路边摊买一个煎饼
            battercake=new BaseBattercake();
            //煎饼有点小，想在加个鸡蛋
            battercake=new EggDecorator(battercake);
            //想在加个鸡蛋
            battercake=new EggDecorator(battercake);
            //想在加个香肠
            battercake=new SausageDecorator(battercake);
            //和静态代理最大的区别就是职责不同
            //静态代理不一定要满足is-a的关系
            //静态代理会做功能增强，同一个职责变得不一样
            System.out.println(battercake.getMsg()+"总价："+battercake.getPrice());
        }
    }

测试结果

煎饼加一个鸡蛋加一个鸡蛋+1根香肠总价：9
    
    Process finished with exit code 0

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