//构建器抽象类，为不同类的实现提供
public interface Builder<T> {public T build();
}/*** @描述: 营养表*/
public class NutritionFacts {private final int servingSize;// requiredprivate final int servings;// requiredprivate final int calories;// optionalprivate final int fat;// optionalprivate final int sodium;// optionalprivate final int carbohydrate;// optionalpublic static class Builder1 implements Builder<NutritionFacts>{private final int servingSize;// required 食用分量private final int servings;// required （食品等的）一份private int calories;// optional 卡路里 private int fat;// optionalprivate int sodium;// optional 钠private int carbohydrate;// optional 碳水化合物；糖类public Builder1(int servingSize,int servings){this.servingSize = servingSize;this.servings = servings;}public Builder1 calories(int calories) {this.calories = calories;return this;}public Builder1 fat(int fat) {this.fat = fat;return this;}public Builder1 sodium(int sodium) {this.sodium = sodium;return this;}public Builder1 carbohydrate(int carbohydrate) {this.carbohydrate = carbohydrate;return this;}@Overridepublic NutritionFacts build() {return new NutritionFacts(this);}}private NutritionFacts(Builder1 builder){this.servingSize = builder.servingSize;this.servings = builder.servings;this.calories = builder.calories;this.fat = builder.fat;this.sodium = builder.sodium;this.carbohydrate = builder.carbohydrate;}public static void main(String[] args) {NutritionFacts cocacola = new NutritionFacts.Builder1(240, 80).calories(100).sodium(35).carbohydrate(27).build();}
}
为非必须参数设置值，返回Build自身可以把调用链接起来
好处：
1、可以用单个builder创建多个对象，builder的参数可以在创建对象期间调整，可以随着对象不同而改变。builder可以自动填充某些域，例如每次创建对象时自动增加序号。
2、这是一个很好的抽象工厂（abstract factory）。客户端只要将这样一个builder传给方法，该方法能为客户端创建一个或多个对象。
一个通用类型的bulider
public interface Builder<T>{public T build();
}