读《effective java》笔记一：遇到多个构造器参数时要考虑用构造器

  第二条  遇到多个构造器参数时要考虑用构造器

这里考虑的是参数多的情况，如果参数个数比较少，那直接采用一般的构造方法就可以了。
   书中介绍了写构造方法的时候几种方式：
    1. 重叠构造方法模式:
       缺点：有许多参数的时候，客户端代码会很难写，而且较难以阅读。

     2. javaBeans模式：
       缺点：  
            在构造过程中JavaBean可能处于不一致的状态，类本身无法判断是否有效性。
            类做成不可变的可能。

     3. builder模式：
       优点：
            在build方法生成对象的时候，可以做检查，判断是否符合要求
            参数灵活
       缺点：
            创建对象必须先创建构造器，如果对性能要求非常高的应用少用为妙



具体实现代码：

1.重叠构造方法模式：

public class NutritionFacts {
    private final int servingSize;
    
    private final int serviings;
    
    private final int calories;
    
    private final int fat;
    
    private int sodium;
    
    private int carbohydrate;
    
    public NutritionFacts(int servingSize, int serviings){
        this(servingSize, serviings, 0);
    }
    
    public NutritionFacts(int servingSize, int serviings, int calories){
        this(servingSize, serviings, calories, 0);
    }
    
    public NutritionFacts(int servingSize, int serviings, int calories, int fat){
        this(servingSize, serviings, calories, fat,0);
    }
    
    public NutritionFacts(int servingSize, int serviings, int calories, int fat, int sodium){
        this(servingSize, serviings, calories, fat, sodium,0);
    }
    
    public NutritionFacts(int servingSize, int serviings, int calories, int fat, int sodium, int carbohydrate){
        this.servingSize = servingSize;
        this.serviings = serviings;
        this.calories = calories;
        this.fat = fat;
        this.sodium = sodium;
        this.carbohydrate = carbohydrate;
    }
}

2. javaBeans模式：

public class NutritionFacts {
    private  int servingSize;
    
    private  int serviings;
    
    private  int calories;
    
    private  int fat;
    
    private int sodium;
    
    private int carbohydrate;
    
    public NutritionFacts(){}
    
    
    public void setServingSize(int servingSize) {
        this.servingSize = servingSize;
    }

    public void setServiings(int serviings) {
        this.serviings = serviings;
    }

    public void setCalories(int calories) {
        this.calories = calories;
    }

    public void setFat(int fat) {
        this.fat = fat;
    }

    public void setSodium(int sodium) {
        this.sodium = sodium;
    }

    public void setCarbohydrate(int carbohydrate) {
        this.carbohydrate = carbohydrate;
    }

3. builder模式

public class NutritionFacts {
    private final int servingSize;
    private final int serviings;
    private final int calories;
    private final int fat;
    private final int sodium;
    private final int carbohydrate;

    public static class Builder {
        private final int servingSize;
        private final int serviings;

        // 可以为空
        private int calories = 0;
        private int fat = 0;
        private int sodium = 0;
        private int carbohydrate = 0;

        public Builder(int servingSize, int serviings) {
            this.servingSize = servingSize;
            this.serviings = serviings;
        }
        
        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 carbohydrate(int val){
            carbohydrate = val;
            return this;
        }
        
        public NutritionFacts build(){
            return new NutritionFacts(this);
        }
        
    }

    public NutritionFacts(Builder builder) {
        servingSize = builder.servingSize;
        serviings = builder.serviings;
        calories = builder.calories;
        fat = builder.fat;
        sodium = builder.sodium;
        carbohydrate = builder.carbohydrate;
    }
}

这个调用的时候：
NutritionFacts cocaCola = new NutritionFacts.Builder(11,22).calories(1).fat(2).calories(3).build();