设计模式二（建造者模式）

建造者模式

 

 

 

设计模式的关键步骤是

 

 

 

 

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("\n\nNon-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

 

 

 

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。