Java 使用Builder解決構造函數參數過多的問題

原文：https://blog.csdn.net/michael_f2008/article/details/77715075

 

//Builder Pattern
public class NutritionFacts{
    public final int servingSize;
    public final int servings;
    public final int calories;
    public final int fat;
    public final int sodium;
    public final int carbohydrate;

    //靜態內部類Builder
    public static class Builder{
        //必選變量
        private final int servingSize;
        private final int servings;

        //可選變量
        private final int calories = 0;
        private final int fat = 0;
        private final int sodium= 0;
        private final int carbohydrate= 0;

        //Builder的構造函數
        public Builder(int servingSize, int servings){
            this. servingSize = servingSize;
            this.servings = servings;
        }


        //Builder的成員方法返回其自身，所以可以鏈式調用
        //類似於setter()方法
        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;
        }

        //Builder的build方法，返回外部類的實例
        public NutritionFacts build(){
            return new NutritionFacts(this);
        }
    }

    //外部類的構造函數
    private NutritionFacts(Builder build){
        servingSize = build.servingSize;
        servings = build.servings;
        calories = build.calories;
        fat = build.fat;
        sodium = build.sodium;
        carbohydrate = build.carbohydrate;
    }
}

 

示例：

NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8).calories(100).sodium(35).carbohydrate(27).build();