Effective JAVA 创建和销毁对象 遇到多参构造器考虑使用构建器

//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;// required
    private final int servings;// required
    private final int calories;// optional
    private final int fat;// optional
    private final int sodium;// optional
    private final int carbohydrate;// optional

    public 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;// optional
        private 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;
        }
        @Override
        public 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();  
}