Storing integer values as constants in Enum manner in java

Question

I m currently creating integer constants in the following manner   public class Constants       public static int SIGN CREATE 0      public static int SIGN CREATE 1      public static int HOME SCREEN 2      public static int REGISTER SCREEN 3      When i try to do this in enum manner   public enum PAGE SIGN CREATE SIGN CREATE HOME SCREEN REGISTER SCREEN    and When i used PAGE SIGN CREATE it should return 1

User · Answer

You can use ordinal  So PAGE SIGN CREATE ordinal   returns 1   EDIT   The only problem with doing this is that if you add  remove or reorder the enum values you will break the system  For many this is not an issue as they will not remove enums and will only add additional values to the end  It is also no worse than integer constants which also require you not to renumber them  However it is best to use a system like   public enum PAGE    SIGN CREATE0 0   SIGN CREATE 1   HOME SCREEN 2   REGISTER SCREEN 3     private int id     PAGE int id       this id   id         public int getID        return id           You can then use getID  So PAGE SIGN CREATE getID   returns 1

User · Answer

You could store that const value in the enum like so  But why even use the const  Are you persisting the enum s   public class SO3990319      public static enum PAGE         SIGN CREATE 1         private final int constValue         private PAGE int constValue             this constValue   constValue                 public int constValue              return constValue                   public static void main String   args          System out println  Name         PAGE SIGN CREATE name           System out println  Ordinal      PAGE SIGN CREATE ordinal           System out println  Const        PAGE SIGN CREATE constValue            System out println  Enum      PAGE valueOf  SIGN CREATE              Edit   It depends on what you re using the int s for whether to use EnumMap or instance field    Bloch on Enum instance fields  Item 31  Use instance fields instead of ordinals  Bloch on EnumMap  Item 33  Use EnumMap instead of ordinal indexing

User · Answer

I found this to be helpful   http   dan clarke name 2011 07 enum-in-java-with-int-conversion   public enum Difficulty       EASY 0       MEDIUM 1       HARD 2                  Value for this difficulty            public final int Value       private Difficulty int value                Value   value                Mapping difficulty to difficulty id     private static final Map lt Integer  Difficulty gt   map   new HashMap lt Integer  Difficulty gt         static               for  Difficulty difficulty   Difficulty values                 map put difficulty Value  difficulty                        Get difficulty from value        param value Value        return Difficulty            public static Difficulty from int value                return  map get value

User · Answer

Well  you can t quite do it that way   PAGE SIGN CREATE will never return 1  it will return PAGE SIGN CREATE   That s the point of enumerated types   However  if you re willing to add a few keystrokes  you can add fields to your enums  like this        public enum PAGE          SIGN CREATE 0           SIGN CREATE BONUS 1           HOME SCREEN 2           REGISTER SCREEN 3            private final int value           PAGE final int newValue                value   newValue                     public int getValue     return value            And then you call PAGE SIGN CREATE getValue   to get 0

User · Answer

if you want to be able to convert integer back to corresponding enum with selected value see Constants forValue      in below auto generated code but if not the answer of BlairHippo is best way to do it   public enum Constants   SIGN CREATE 0   SIGN CREATE 1   HOME SCREEN 2   REGISTER SCREEN 3        public static final int SIZE   java lang Integer SIZE       private int intValue      private static java util HashMap lt Integer  Constants gt  mappings      private static java util HashMap lt Integer  Constants gt  getMappings                 if  mappings    null                        synchronized  Constants class                                if  mappings    null                                        mappings   new java util HashMap lt Integer  Constants gt                                                       return mappings             private Constants int value                intValue   value          getMappings   put value  this              public int getValue                 return intValue             public static Constants forValue int value                return getMappings   get value

User · Answer

The most common valid reason for wanting an integer constant associated with each enum value is to interoperate with some other component which still expects those integers  e g  a serialization protocol which you can t change  or the enums represent columns in a table  etc    In almost all cases I suggest using an EnumMap instead   It decouples the components more completely  if that was the concern  or if the enums represent column indices or something similar  you can easily make changes later on  or even at runtime if need be     private final EnumMap lt Page  Integer gt  pageIndexes   new EnumMap lt Page  Integer gt  Page class    pageIndexes put Page SIGN CREATE  1      etc         int createIndex   pageIndexes get Page SIGN CREATE     It s typically incredibly efficient  too   Adding data like this to the enum instance itself can be very powerful  but is more often than not abused   Edit  Just realized Bloch addressed this in Effective Java   2nd edition  in Item 33   Use EnumMap instead of ordinal indexing

[java] Storing integer values as constants in Enum manner in java

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