Gettin枚举类型可能不会被实例化异常 [英] Gettin enum types may not be instantiated Exception

问题描述

我正在获得RuntimeException

I am getting RuntimeException

枚举类型可能未被实例化

Enum types may not be instantiated

我不知道为什么。我想要的是用一个整数值来识别一年，因为我有9，所以其他方法的年份是2006.代码：

I don't know why. What I want is to identify a year by an integer value like i have 9 so the year for other Methods is 2006. Code:

public class P21Make {

    enum Catalog {
        year2005(9),year2006(12),year2007(15),year2008(18),
        year2009(21),year2010(23),year2011(25),year2012(28),
        year2013(31),year2014(33),year2015(36),year2016(39),
        year2017(42),year2018(45),year2019(48),year2020(51);

        private int id;    

        Catalog(int c){
            this.id=c;
        }
    }

    public P21Make() {
        Catalog c = new Catalog(9);   // The Exception 
    }
}

推荐答案

你不能像这样实例化枚举。你有2个可能性

You cannot instantiate enum like this . You have 2 possiblities

1.Catalog c = Catalog.year2005;

2。通过添加可以根据代码（整数值）返回您的枚举的方法，在您的枚举中进行以下更改。例如

2. Make the following change in your enum by adding a method that can return you enum based on code(integer value) . E.g.

   enum Catalog {
      year2005(9),year2006(12),year2007(15),year2008(18),
      year2009(21),year2010(23),year2011(25),year2012(28),
      year2013(31),year2014(33),year2015(36),year2016(39),
      year2017(42),year2018(45),year2019(48),year2020(51);
      private int id;

      Catalog(int c){
         this.id=c;
      }


      static Map<Integer, Catalog> map = new HashMap<>();

      static {
         for (Catalog catalog : Catalog.values()) {
            map.put(catalog.id, catalog);
         }
      }

      public static Catalog getByCode(int code) {
         return map.get(code);
      }
   }

然后分配像这样

Catalog c = Catalog.getByCode(9);

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