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设计模式二(建造者模式)

开发技术 开发技术 2022-10-11 次浏览

建造者模式

设计模式二(建造者模式)

 

 

 

设计模式的关键步骤是

设计模式二(建造者模式)

 

 

 

 

import java.util.ArrayList;
import java.util.List;
 
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());
      }        
   }    
}

 

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;
   }
}

  

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("nnNon-Veg Meal");
      nonVegMeal.showItems();
      System.out.println("Total Cost: " +nonVegMeal.getCost());
   }
}

  可以看出 主干是BuilderPatternDemo 使用 MealBuilder ,而Meal 是MealBuilder 的成员变量,Item又组成了Meal

BuilderPatternDemo (运行代码)  ——MealBuilder(顶层的构造器java类)——Meal (次级的构造器java类)——Item(底层的物品,接口)

在其中Meal是成品, Item是最重要的抽象属性,提供了下面大多数类的属性。

实体类实现Item后可以变为

设计模式二(建造者模式)

 

 

 

public interface Item {
   public String name();
   public Packing packing();
   public float price();    
}
public interface Packing {
   public String pack();
}
public class Wrapper implements Packing {
 
   @Override
   public String pack() {
      return "Wrapper";
   }
}
public class Bottle implements Packing {
 
   @Override
   public String pack() {
      return "Bottle";
   }
}
public abstract class Burger implements Item {
 
   @Override
   public Packing packing() {
      return new Wrapper();
   }
 
   @Override
   public abstract float price();
}
public abstract class ColdDrink implements Item {
 
    @Override
    public Packing packing() {
       return new Bottle();
    }
 
    @Override
    public abstract float price();
}

接下来的核心是Item如何被实现,抽象类通过实现Item,重写了部分属性。其中,最关键的是,Packing作为返回值时候,可以返回Packing子类,变相拓展了Packing的选择范围。

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