Builder模式--用于多个构造器参数时使用

package com.zxm;

/**
 * Creator:zxm
 * Date:2017/2/23
 * Description:
 */
public class NutritionFacts {
    private final int servingSize ;
    private final int servings ;
    private final int calories ;
    private final int fat ;
    private final int sodium ;
    private final int carbonhydrate ;

    public static class Builder{
        //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 carbonhydrate = 0;

        public Builder(int servingSize,int servings){
            this.servingSize = servingSize;
            this.servings = servings;
        }

        public Builder calories(int val){
            calories = val;
            return this;
        }

        public Builder fat(int val){
            fat = val;
            return this;
        }

        public Builder sodium(int val){
            sodium = val;
            return this;
        }

        public Builder carbonhydrate(int val){
            carbonhydrate = val;
            return this;
        }

        public NutritionFacts bulid(){
            return new NutritionFacts(this);
        }
    }

    private NutritionFacts(Builder builder){
        servingSize = builder.servingSize;
        servings = builder.servings;
        calories = builder.calories;
        fat  = builder.fat;
        sodium = builder.sodium;
        carbonhydrate = builder.carbonhydrate;
    }

    public static void main(String[] args) {
        NutritionFacts cocaCola = new NutritionFacts.Builder(240,8).calories(100).sodium(35).carbonhydrate(27).bulid();
    }
}
Bulider模式：

不直接生成想要的对象，而是让客户端利用所有必要参数调用构造器（或者静态工厂），得到一个Builder对象。然后在Builder对象上调用类似setter的方法来设置每个相关的可选参数。最后，客户端调用无参的build()方法来生成不可变的对象。这个Builder是它构建的类的静态成员类。

Builder的setter方法返回builder本身，以便把调用链接起来。