纯粹学习笔记。

使用多个简单的对象构造成复杂对象。
一个builder会一步一步的构造成最终的对象。该builder类是独立于其他对象的。
主要用在一个复杂对象的创建。每个子对象实现逻辑可以改变，但是组合在一起之后的逻辑不变。
适用场景:生成的对象具有复杂的内部结构。生成的对象内部本身相互依赖。

案例

一个套餐: 汉堡(Burger)和冷饮(Colddrink)，汉堡可以是素食汉堡和鸡肉汉堡，包装是纸质的。冷饮可以是可乐(coke)和百事(pepsi)，包装是瓶子。

Item.java

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

Packing.java

  public interface Packing {
    public String pack();
  }

创建Packing接口的实体类。

Wrapper.java

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

Bottle.java

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

Burger.java

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

ColdDrink.java

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

VegBurger.java

  public class VegBurger extends Burger {
    @Override
    public String name() {
      return "VegBurger";
    }
    @Override
    public float price() {
      return 25.0f;
    }
  }

ChickenBurger.java

  public class ChickenBurger extends Burger {
    @Override
    public String name() {
      return "ChickenBurger";
    }
    @Override
    public float price() {
      return 50.5f;
    }
  }

Coke.java

  public class Coke extends ColdDrink {
    @Override
    public String name() {
      return "Coke";
    }
    @Override
    public float price() {
      return 30.0f;
    }
  }

Pepsi.java

  public class Pepsi extends ColdDrink {
    @Override
    public String name() {
      return "Pepsi";
    }
    @Override
    public float price() {
      return 35.0f;
    }
  }

Meal.java

  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 getCoat() {
      float coats = 0.0f;
      for (Item item : items) {
        coat += item.price();
      }
      return coats;
    }
  }

MealBuilder.java

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;
   }
}