Java创建和销毁对象的几种方式

悠悠 2022-07-13 06:00 232阅读 0赞

# 创建对象的几种方式 #

1.  构造器
2.  静态工厂方法
3.  通过Builder  
    不直接生成想要的对象，而是让客户端利用所有必要的参数调用构造器，得到一个builder对象，然后客户端在builder对象上调用类似于setter的方法，来设置每个可选参数，最后在客户端调用无参的build()方法来生成对象。下面是一个简单的示例：

//builder pattern
    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 carbohydrate;
    
    
        public static class Builder{ 
            //required
            private final int servingSize;
            private final int servings;
    
            //optional
            private int calories =0;
            private int fat =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 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;
            }
    
            //build 构造对象
            public NutritionFacts build(){
                return new NutritionFacts(this);
            }
        }
    
        private NutritionFacts(Builder builder){
            servingSize = builder.servingSize;
            servings = builder.servings;
            calories = builder.calories;
            fat = builder.fat;
            sodium = builder.sodium;
            carbohydrate = builder.carbohydrate;
        }
    }
    
    //客户端调用
    NutritionFacts cocaCola = new NutritionFacts.Builder(20, 8).calories(100).sodium(35).carbohydrate(27).build()；