设计模式之建造者模式(四)

设计模式之建造者模式(四)

建造者模式（Builder Pattern）使用多个简单的对象一步一步构建成一个复杂的对象。这种类型的设计模式属于创建型模式，它提供了一种创建对象的最佳方式。

一个 Builder 类会一步一步构造最终的对象。该 Builder 类是独立于其他对象的。

建造者的创建步骤：

1.创建一个表示食物条目和食物包装的接口

2.创建实现 Packing 接口的实体类

3.创建实现 Item 接口的抽象类，该类提供了默认的功能

4.创建扩展了 Burger 和 ColdDrink 的实体类

5.创建一个 Meal 类，带有上面定义的 Item 对象

6.创建一个 MealBuilder 类，实际的 builder 类负责创建 Meal 对象

7.使用 MealBuider 来演示建造者模式（Builder Pattern）

步骤一

public interface Item {   public String name();   public Packing packing();   public float price();}

public interface Packing {   public String pack();}

步骤二

public class Wrapper implements Packing {   @Override   public String pack() {      return "Wrapper";   }}

public class Bottle implements Packing {   @Override   public String pack() {      return "Bottle";   }}

步骤三

public abstract class Burger implements Item {   @Override   public Packing packing() {      return new Wrapper();   }   @Override   public abstract float price();}

public abstract class ColdDrink implements Item {@Overridepublic Packing packing() {       return new Bottle();}@Overridepublic abstract float price();}

步骤四

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";   }}

步骤五

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());      }   }}

步骤六

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;   }}

步骤七

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());   }}