Java設計模式（3）-裝飾者模式

一. 學習專案：咖啡館訂單系統

  咖啡館訂單：
  1）咖啡種類：Espresso,ShortBlack,LongBlack,Decaf
  2)調料：Milk,Soy,Chocolate
  3)擴充套件性好，改動方便，維護方便

1.一個差的解決方案：

       飲品超類：
      （1）<abstract>Drink
           description
           getDescription()
           cost()
           
       咖啡單品：
       (1) Decaf
           cost()
           
       (2) ShortBlack
           cost()              
      （3） LongBlack
            cost()
       (4) Espresso
            cost()
        
       新增調料咖啡：
       （1）Espresso && Milk
            cost()
            
       （3）Espresso  && Soy
            cost()
                 
       （3）Espresso && Milk && Soy
            cost()       
            
         ...   
         ...
   擴充性很差，到時可能遇見類爆炸。。。

2. 一個較好的設計方案

飲品超類：
    <abstract>Drink
        desciprtion
        milk
        soy
        chocolate
        
     getDescription()
     cost()
     hasMilk()
     setMilk()
     hasSoy()
     setSoy()
     hasChocolate()
     setChocolate()
 
  咖啡單品：
       (1) Decaf
           cost()
           
       (2) ShortBlack
           cost()              
      （3） LongBlack
            cost()
       (4) Espresso
            cost()
  
 存在一些問題：
   （1）增刪調料種類
   （2）新增多份問題 

3.使用裝飾者模式

 瞭解裝飾者模式
 （1）裝飾者模式就像打包的一個快遞
      1）主體：陶瓷 ，衣服
      2）包裝：報紙填充，塑料泡沫，紙盒，木盒
 （2）Component:
  
  (3)ConcreteComponent 和 Decorator        
  
  (4)裝飾者模式：動態的將新的功能附加到物件上。在物件的擴充套件方面，它比繼承更有彈性。

設計方案：

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

3.
    
     咖啡單品：
     (1) Decaf
         cost()
         
     (2) ShortBlack
         cost()              
    （3） LongBlack
          cost()
     (4) Espresso
          cost()
          
     調料單品：
     (1)Chocolate
           getDescription()
           cost()
     (2)Milk
           getDescription()
           cost()
     (3)Soy
           getDescription()
           cost()               
    

程式碼實現：

(1) Drink

package com.java.keen.coffeebar;
//飲品類：描述，價格
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;
    }
    
    //花費是一個抽象方法，因為不知道顧客具體選喝啥
    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)各種咖啡單品

//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)各種調料單品：

//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)測試類

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

個人在極客學院的學習的筆記