Java设计模式（3）-装饰者模式

一. 学习项目：咖啡馆订单系统

  咖啡馆订单：
  1）咖啡种类：Espresso,ShortBlack,LongBlack,Decaf
  2)调料：Milk,Soy,Chocolate
  3)扩展性好，改动方便，维护方便

1.一个差的解决方案：

       饮品超类：
      （1）<abstract>Drink
           description
           getDescription()
           cost()
           
       咖啡单品：
       (1) Decaf
           cost()
           
       (2) ShortBlack
           cost()              
      （3） LongBlack
            cost()
       (4) Espresso
            cost()
        
       添加调料咖啡：
       （1）Espresso && Milk
            cost()
            
       （3）Espresso  && Soy
            cost()
                 
       （3）Espresso && Milk && Soy
            cost()       
            
         ...   
         ...
   拓展性很差，到时可能遇见类爆炸。。。

2. 一个较好的设计方案

饮品超类：
    <abstract>Drink
        desciprtion
        milk
        soy
        chocolate
        
     getDescription()
     cost()
     hasMilk()
     setMilk()
     hasSoy()
     setSoy()
     hasChocolate()
     setChocolate()
 
  咖啡单品：
       (1) Decaf
           cost()
           
       (2) ShortBlack
           cost()              
      （3） LongBlack
            cost()
       (4) Espresso
            cost()
  
 存在一些问题：
   （1）增删调料种类
   （2）添加多份问题 

3.使用装饰者模式

 了解装饰者模式
 （1）装饰者模式就像打包的一个快递
      1）主体：陶瓷 ，衣服
      2）包装：报纸填充，塑料泡沫，纸盒，木盒
 （2）Component:
  
  (3)ConcreteComponent 和 Decorator        
  
  (4)装饰者模式：动态的将新的功能附加到对象上。在对象的扩展方面，它比继承更有弹性。

设计方案：

1.
<abstract>Drink
    description
    getDescription()
    cost()
  
2.
Decorator
   Drink obj
   getDescription()
   cost()
   ...

3.
    
     咖啡单品：
     (1) Decaf
         cost()
         
     (2) ShortBlack
         cost()              
    （3） LongBlack
          cost()
     (4) Espresso
          cost()
          
     调料单品：
     (1)Chocolate
           getDescription()
           cost()
     (2)Milk
           getDescription()
           cost()
     (3)Soy
           getDescription()
           cost()               
    

代码实现：

(1) Drink

package com.java.keen.coffeebar;
//饮品类：描述，价格
public abstract class Drink {
    public String description = "";
    private float price = 0f;
    
    public String getDescription() {
        return description+"  "+this.getPrice();
    }
    public void setDescription(String description) {
        this.description = description;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
    
    //花费是一个抽象方法，因为不知道顾客具体选喝啥
    public abstract float cost();
}

(2)Decorator

package com.java.keen.coffeebar.decorator;

import com.java.keen.coffeebar.Drink;

public class Decorator extends Drink{
   private Drink obj;
   public Decorator(Drink obj) {
       this.obj = obj;
   }
    @Override
    public float cost() {
        
        return super.getPrice() +obj.cost();
    }
   public String getDescription() {
       return super.description+"+"+super.getPrice()+"&&"+obj.getDescription();
   }
}

(3)Coffee

package com.java.keen.coffeebar.coffee;

import com.java.keen.coffeebar.Drink;

public class Coffee extends Drink {

    @Override
    public float cost() {
        
        return super.getPrice();
    }
    

}

(4)各种咖啡单品

//1.Decaf
package com.java.keen.coffeebar.coffee;

public class Decaf  extends Coffee{
    public Decaf() {
        super.setDescription("Decaf");
        super.setPrice(3.0f);
    }

}


//2.Espresso
package com.java.keen.coffeebar.coffee;

public class Espresso extends Coffee{
    public Espresso() {
        super.setDescription("Espresso");
        super.setPrice(4.0f);
    }

}

//3.LongBlack
package com.java.keen.coffeebar.coffee;

public class LongBlack  extends Coffee{
    public LongBlack() {
        super.setDescription("LongBlack");
        super.setPrice(5.0f);
    }

}

//4.ShortBlack 
package com.java.keen.coffeebar.coffee;

public class ShortBlack extends Coffee{
    public ShortBlack () {
        super.setDescription("ShortBlack ");
        super.setPrice(6.0f);
    }

}

(5)各种调料单品：

//1.Chocolate
package com.java.keen.coffeebar.decorator;

import com.java.keen.coffeebar.Drink;

public class Chocolate extends Decorator{

    public Chocolate(Drink obj) {
        super(obj);
        // TODO Auto-generated constructor stub
        super.setDescription("Chocolate");
        super.setPrice(3.0f);
    }

}


//2.Milk
package com.java.keen.coffeebar.decorator;

import com.java.keen.coffeebar.Drink;

public class Milk extends Decorator{

    public Milk(Drink obj) {
        super(obj);
        // TODO Auto-generated constructor stub
        super.setDescription("milk");
        super.setPrice(2.5f);
    }

}



//3.Soy
package com.java.keen.coffeebar.decorator;

import com.java.keen.coffeebar.Drink;

public class Soy extends Decorator{

    public Soy(Drink obj) {
        super(obj);
        // TODO Auto-generated constructor stub
        super.setDescription("soy");
        super.setPrice(1.5f);
    }

}

(6)测试类

package com.java.keen.coffeebar;

import com.java.keen.coffeebar.coffee.*;
import com.java.keen.coffeebar.decorator.*;

public class CoffeeBar {
    public static void main(String[] args) {
         Drink order;
         order = new Decaf();
         System.out.println("order1 price:  " +order.cost());
         System.out.println("order1 desc :  "+order.getDescription());
    
         System.out.println("***************");
         order = new LongBlack();
         order = new Milk(order);
         order =new Chocolate(order);
         order =new Chocolate(order);
         System.out.println("order2 price:  " +order.cost());
         System.out.println("order2 desc :  "+order.getDescription());
    
    
    }
}

output:

order1 price:  3.0
order1 desc :  Decaf  3.0
***************
order2 price:  13.5
order2 desc :  Chocolate+3.0&&Chocolate+3.0&&milk+2.5&&LongBlack  5.0

个人在极客学院的学习的笔记