《Effective Java》之Builder Pattern

如果类的构造器或静态工厂具有多个输入参数，在调用Object(1.0，2.0，3.0，4.0，5.0，6.0)的时候你也许会记不住这么多参数具体对应的属性，再者如果一个类具有较多的需要初始化的属性的时候，那么它的构造函数想必也是需要多个（依然免不了前面看起来较多的参数传入），你需要实现具有1，2，，，个参数的构造函数。

那么接下来这样的方法也许能够改变你上面的烦恼。

1.需要构造的类如下：

public class NutritionFacts {   
    //必选参数
    private final int servingSize;
    private final int servings;
    //可选参数
    private final int calories;
    private final int fat;
    private final int sodium;
    private final int carbohydrate;

    public static class Builder{//构造器
        //必选参数
        private final int servingSize;
        private final int servings;
        //可选参数
        private int calories=0;
        private int fat       =0;
        private int sodium=0;
        private int carbohydrate=0;

        public Builder(int servingSzie,int serings) {
            this.servingSize=servingSzie;
            this.servings=serings;
        }
        public Builder calories(int calories) {
            this.calories=calories;
            return this;
        }
        public Builder fat(int fat) {
            this.fat=fat;
            return this;
        }
        public Builder sodium(int sodium) {
            this.sodium=sodium;
            return this;
        }
        public Builder carbohydrate(int carbohydrate) {
            this.carbohydrate=carbohydrate;
            return this;
        }
        public NutritionFacts builder() {
            return new NutritionFacts(this);
        }
    }
    public NutritionFacts(Builder builder) {
        servingSize=builder.servingSize;
        servings=builder.servings;
        calories=builder.calories;
        fat=builder.fat;
        sodium=builder.sodium;
        carbohydrate=builder.carbohydrate;
    }
}

2.调用生成对象如下：

public class Main {

    public static void main(String[] args) {
        //分别设置每一个参数，
        NutritionFacts nutritionFacts=new NutritionFacts.Builder(15, 20).
                calories(1).carbohydrate(2).fat(3).sodium(4).builder();
    }

}

参考资料：
《Effective Java》