Effective Java Second Edition --- Builder Pattern

如果类的构造器或者静态工厂中有多个参数，设计这种类时，Builder模式是一种不错的选择，特别是当大多数参数是可选的时候。

与使用传统的重载构造函数模式相比，使用Builder模式的客户端代码更易于阅读和编写，构造器也比javabeens更加安全。

代码如下：

 /**
  * Created by zhanga.fnst on 2016/3/14.
  */
 public class NutritionFacts {
     private final int servingSize;
     private final int servings;
     private final int calories;
     private final int flat;
     private final int sodium;
     private final int carbohydrate;

     public  static class Builder{
         //required parameters
         private final int servingSize;
         private final int servings;

         //Optional parameters
         private  int calories = 0;
         private  int flat = 0;
         private  int sodium = 0;
         private  int carbohydrate = 0;

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

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

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

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

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

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

     private NutritionFacts(Builder builder){
         servingSize = builder.servingSize;
         servings = builder.servings;
         calories = builder.calories;
         flat = builder.flat;
         sodium = builder.sodium;
         carbohydrate = builder.carbohydrate;
     }
 }

main方法：

 /**
  * Created by zhanga.fnst on 2016/3/14.
  */
 public class TestMain {
     NutritionFacts cocaCola = new NutritionFacts.Builder(240,8).
             calories(100).sodium(35).carbohydrate(27).build();
 }