Gettin enum types may not be instantiated Exception

问题:

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      } } 

回答1:

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 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); 

回答2:

You Should not call constructor in enum.

You should call Catalog c = Catalog.year2005; like that.

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