23種設計模式（4）建造者模式（Builder模式）

建造者模式是一步一步創建一個複雜的對象，它允許用戶只通過指定複雜對象的類型和內容就可以構建它們，用戶不需要知道內部的具體構建細節

以肯德基套餐爲例
1、產品角色
創建一個產品類Meal

public class Meal {
    private String food;
    private String drink;

    public String getFood() {
        return food;
    }	
    public void setFood(String food) {
        this.food = food;
    }	
    public String getDrink() {
        return drink;
    }	
    public void setDrink(String drink) {
        this.drink = drink;
    }
}

2、抽象建造者
創建一個Product對象的各個部件指定的抽象類

public abstract class MealBuilder {
    Meal meal = new Meal();
    
    public abstract void buildFood();
    
    public abstract void buildDrink();
    
    public Meal getMeal(){
        return meal;
    }
}

3、具體建造者
繼承抽象類，構建和裝配各個部件
A套餐：

public class MealA extends MealBuilder{
    public void buildDrink() {
        meal.setDrink("可樂");
    }
    public void buildFood() {
        meal.setFood("薯條");
    }
}

B套餐：

public class MealB extends MealBuilder{
    public void buildDrink() {
        meal.setDrink("檸檬果汁");
    }
    public void buildFood() {
        meal.setFood("雞翅");
    }
}

4、指揮官
構建一個使用Builder接口的對象

public class KFCWaiter {
    private MealBuilder mealBuilder;
    
    public KFCWaiter(MealBuilder mealBuilder) {
        this.mealBuilder = mealBuilder;
    }    
    public Meal construct(){
        //準備食物
        mealBuilder.buildFood();
        //準備飲料
        mealBuilder.buildDrink();        
        //準備完畢，返回一個完整的套餐給客戶
        return mealBuilder.getMeal();
	 }
}

5、測試類

public class Test {
   public static void main(String[] args) {
        //套餐A
        MealA a = new MealA();
        //準備套餐A的服務員
        KFCWaiter waiter = new KFCWaiter(a);
        //獲得套餐
        Meal mealA = waiter.construct();      
        System.out.print("套餐A的組成部分:");
        System.out.println("食物："+mealA.getFood()+"；   "+"飲品："+mealA.getDrink());
    }
}