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面向对象设计之建造者模式

2019-05-12 分类 编程基础, 设计模式 作者 云海鹰影 ~5.44K 字

建造者模式使用多个简单的对象一步一步构建成一个复杂的对象。可以将复杂对象的创建过程独立出来，简化逻辑。

直接从代码感受吧

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//考虑肯德基点餐，一个典型的套餐可以是一个汉堡和一杯冷饮。汉堡可以是素食汉堡或鸡肉汉堡，它们是包在纸盒中。冷饮可以是可口可乐或百事可乐，它们是装在瓶子中。

//先创建一个表示食物条目和食物包装的接口。
public interface Item {
   public String name();
   public Packing packing();
   public float price();
}
public interface Packing {
   public String pack();
}

//实现包装的实体类。
public class Wrapper implements Packing {
   @Override
   public String pack() {
      return "Wrapper";
   }
}
public class Bottle implements Packing {
   @Override
   public String pack() {
      return "Bottle";
   }
}

//抽象出汉堡类和冷饮类
public abstract class Burger implements Item {
   @Override
   public Packing packing() {
      return new Wrapper();
   }
}
public abstract class ColdDrink implements Item {
    @Override
    public Packing packing() {
       return new Bottle();
    }
}

//实现出汉堡和冷饮的具体类
public class VegBurger extends Burger {
   @Override
   public float price() {
      return 25.0f;
   }
   @Override
   public String name() {
      return "Veg Burger";
   }
}
public class ChickenBurger extends Burger {
   @Override
   public float price() {
      return 50.5f;
   }
   @Override
   public String name() {
      return "Chicken Burger";
   }
}
public class Coke extends ColdDrink {
   @Override
   public float price() {
      return 30.0f;
   }
   @Override
   public String name() {
      return "Coke";
   }
}
public class Pepsi extends ColdDrink {
   @Override
   public float price() {
      return 35.0f;
   }
   @Override
   public String name() {
      return "Pepsi";
   }
}

至此，组成几分套餐的基本成分就齐了，接下来我们再定义出套餐类

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public class Meal {
   private List<Item> items = new ArrayList<Item>();
	
   public void addItem(Item item){
      items.add(item);
   }
	
   public float getCost(){
      float cost = 0.0f;
      for (Item item : items) {
         cost += item.price();
      }
      return cost;
   }
	
   public void showItems(){
      for (Item item : items) {
         System.out.print("Item : "+item.name());
         System.out.print(", Packing : "+item.packing().pack());
         System.out.println(", Price : "+item.price());
      }
   }
}

有了套餐元素和套餐类，我们就可以创建一个Builder对象，用于创建各种套餐。

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public class MealBuilder {
   public Meal prepareVegMeal (){
      Meal meal = new Meal();
      meal.addItem(new VegBurger());
      meal.addItem(new Coke());
      return meal;
   }
 
   public Meal prepareNonVegMeal (){
      Meal meal = new Meal();
      meal.addItem(new ChickenBurger());
      meal.addItem(new Pepsi());
      return meal;
   }
}

//测试刚刚完成的MealBuilder
public class BuilderPatternDemo {
   public static void main(String[] args) {
      MealBuilder mealBuilder = new MealBuilder();
 
      Meal vegMeal = mealBuilder.prepareVegMeal();
      System.out.println("Veg Meal");
      vegMeal.showItems();
      System.out.println("Total Cost: " +vegMeal.getCost());
 
      Meal nonVegMeal = mealBuilder.prepareNonVegMeal();
      System.out.println("\n\nNon-Veg Meal");
      nonVegMeal.showItems();
      System.out.println("Total Cost: " +nonVegMeal.getCost());
   }
}

有时候可能情况会更复杂一些，我们可能会这样定义MealBuilder:

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public abstract class MealBuilder {
	Meal m;
	public void buildFood();
	public void buildDrink();
	public Meal getMeal() {
		return m;
	}
}
public class VegMealBuilder implements MealBuilder {
    @Override
    public void buildFood() {
       m..addItem(new VegBurger());
    }
    @Override
    public void buildDrink() {
       m..addItem(new Coke());
    }
}
public class NonVegMealBuilder implements MealBuilder {
    @Override
    public void buildFood() {
       m..addItem(new ChickenBurger());
    }
    @Override
    public void buildDrink() {
       m..addItem(new Pepsi());
    }
}

为了让各种不同的建造者工作起来，就需要引入监工(Director)角色，通过监工来实现使不同的建造者通过统一的流程创建出不同的产品。

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public class MealDirector {
	MealBuilder builder;
	
	MealDirector(MealBuilder b)  {
		this.builder = b;
	}
    public void setBuilder(MealBuilder b) {
        this.builder = b;
    }
	
	public Meal buildMeal() {
		this.builder.buildFood();
		this.builder.buildDrink();
		return this.builder.getMeal();
	}
}

public class BuilderPatternDemo {
   public static void main(String[] args) {
		VegMealBuilder b1 = new VegMealBuilder();
		NonVegMealBuilder b2 = new NonVegMealBuilder();
		
		MealDirector director = new MealDirector(b1);
		Meal vegMeal = director.buildMeal();
		System.out.println("Veg Meal");
		vegMeal.showItems();
		System.out.println("Total Cost: " +vegMeal.getCost());
	   
	   director.setBuilder(b2);
		Meal nonVegMeal = director.buildMeal();
		System.out.println("\n\nNon-Veg Meal");
nonVegMeal.showItems();
		System.out.println("Total Cost: " +nonVegMeal.getCost());
	}
}
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最后编辑：2021-02-01