1.建造者模式
使用简单的对象构造复杂的对象。
2.举例:
我们假设一个快餐店的商业案例,其中,一个典型的套餐可以是一个汉堡(Burger)和一杯冷饮(Cold drink)。汉堡(Burger)可以是素食汉堡(Veg Burger)或鸡肉汉堡(Chicken Burger),它们是包在纸盒中。冷饮(Cold drink)可以是可口可乐(coke)或百事可乐(pepsi),它们是装在瓶子中。
我们将创建一个表示食物条目(比如汉堡和冷饮)的Food 接口和实现 Food 接口的实体类,以及一个表示食物包装的 Packing 接口和实现 Packing 接口的实体类,汉堡是包在纸盒中,冷饮是装在瓶子中。
然后我们创建一个 Meal 类,带有 Item 的 ArrayList 和一个通过结合 Item 来创建不同类型的 Meal 对象的 MealBuilder。BuilderPatternDemo,我们的演示类使用 MealBuilder 来创建一个 Meal。
3.UML
4.代码实现
public interface Food { /** * 食物的名称 * @return */ String name(); /** * 食物的包装方式 * @return */ Packing packing(); /** * 食物的价格 * @return */ BigDecimal price(); }
public interface Packing { String pack(); }
public class Bottle implements Packing{ @Override public String pack() { return "Bottle"; } }
public class Wrapper implements Packing{ @Override public String pack() { return "Wrapper"; } }
public abstract class Burger implements Food{ @Override public Packing packing() { return new Wrapper(); } }
public abstract class ColdDrink implements Food{ @Override public Packing packing(){ return new Bottle(); } }
public class ChickenBurger extends Burger{ @Override public String name() { return "Chicken Burger"; } @Override public BigDecimal price() { return BigDecimal.valueOf(50.5); } }
public class VegBurger extends Burger{ @Override public String name() { return "Veg Burger"; } @Override public BigDecimal price() { return BigDecimal.valueOf(25.0); } }
public class CocaCola extends ColdDrink{ @Override public String name() { return "CocaCola"; } @Override public BigDecimal price() { return BigDecimal.valueOf(30.0); } }
public class PepsiCola extends ColdDrink{ @Override public String name() { return "PepsiCola"; } @Override public BigDecimal price() { return BigDecimal.valueOf(35.0); } }
public class Meal { private List<Food> items = new ArrayList<>(); public void addItem(Food item) { items.add(item); } public BigDecimal getCost() { BigDecimal cost = BigDecimal.ZERO; for (Food item : items) { cost = cost.add(item.price()); } return cost; } public void showItems() { for (Food 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 static Meal prepareVegMeal() { Meal meal = new Meal(); meal.addItem(new VegBurger()); meal.addItem(new CocaCola()); return meal; } public static Meal prepareNonVegMeal() { Meal meal = new Meal(); meal.addItem(new ChickenBurger()); meal.addItem(new PepsiCola()); return meal; } }
5 测试类
public class MealBuilderTest { @Test public void test() { Meal nonvegmeal = MealBuilder.prepareNonVegMeal(); System.out.println("Non-Veg Meal"); nonvegmeal.showItems(); System.out.println("Total Cost: " + nonvegmeal.getCost()); Meal vegMeal = MealBuilder.prepareVegMeal(); System.out.println("\n\nVeg Meal"); vegMeal.showItems(); System.out.println("Total Cost: " + vegMeal.getCost()); } }
测试结果:
Non-Veg Meal Item : Chicken Burger, Packing : Wrapper, Price : 50.5 Item : PepsiCola, Packing : Bottle, Price : 35.0 Total Cost: 85.5 Veg Meal Item : Veg Burger, Packing : Wrapper, Price : 25.0 Item : CocaCola, Packing : Bottle, Price : 30.0 Total Cost: 55.0