Zion Zion - 1 month ago 12
Java Question

Gettin enum types may not be instantiated Exception

I am getting RuntimeException


Enum types may not be instantiated


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
}
}

Answer

You cannot instantiate enum like this . You have 2 possiblities

1.Catalog c = Catalog.year2005;

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);
      }
   }

and then assign like this

Catalog c = Catalog.getByCode(9);
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