Design Pattern - Factory Pattern (一)

SimpleFactory

假設有個飲料店

public class BeverageShop{

   Beverage beverage;

   public Beverage orderBeverage(String type){

       if(type.equals("紅茶")){
           beverage = new BlackTea();
       }else if(type.equals("奶茶")){
           beverage = new MilkTea();
       }

       beverage.prepare();
       beverage.box();
       return beverage;
   }
}

缺點:
1.未來要增加飲料種類, 要修改這class
2.prepare(),box()等等, 是固定不變的

Factory Pattern 的概念是怎麼把new一個object的處理封裝起來

現在把會變動的地方拉出來

public class SimpleBeverageFactry{

   public static Beverage createBeverage(String type){

       if(type.equals("紅茶")){
           beverage = new BlackTea();
       }else if(type.equals("奶茶")){
           beverage = new MilkTea();
       }
       return beverage;
   }
}

public class BeverageShop{

   SimpleBeverageFactry factory;

   //這裡把使用的factory寫死了, 不好
   public BeverageShop(SimpleBeverageFactry factory){
       this.factory = factory;
   }

   public Beverage orderBeverage(String type){

       Beverage beverage = factory.createBeverage(type);

       beverage.prepare();
       beverage.box();
       return beverage;
   }
}

優點:
1.把做飲料的步驟獨立出來, 未來只要有需要飲料的地方, 都可由這產生

上面是用一個factory來new object, 我們再來試試, 用extends

public atstract class BeverageShop{

   public Beverage orderBeverage(String type){

       Beverage beverage = createBeverage(type);

       beverage.prepare();
       beverage.box();
       return beverage;
   }

   //現在new obejct的方式, 就由extends的類別自已實作
   public abstract Beverage createBeverage(String type);
}

public class CocoBeverage extends Beverage{
   public Beverage createBeverage(String type){
       //做出coco獨特的飲料
   }
}
public class QKBeverage extends Beverage{
   public Beverage createBeverage(String type){
   //做出qk caffee獨特的飲料
   }
}

public class demo{
   public static void main(String[] args){
       BeverageShop coco = new CocoBeverage();
       Beverage beverage = coco.orderBeverage();

       xxx
   }
}

寫到這裡, 我覺factory不可能這麼單純, 上面的例子應該很好懂, 跟一般在實作時的寫法類似