Cast Int to enum in Java

Question

What is the correct way to cast an Int to an enum in Java given the following enum   public enum MyEnum       EnumValue1      EnumValue2     MyEnum enumValue    MyEnum  x    Doesn t work

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enum MyEnum       A 0       B 1       private final int value      private MyEnum int val   this value   value       private static final MyEnum   values   MyEnum values     cache for optimization     public static final getMyEnum int value             try               return values value    OOB might get triggered           catch  ArrayOutOfBoundsException e              finally               return myDefaultEnumValue

User · Answer

A good option is to avoid conversion from int to enum  for example  if you need the maximal value  you may compare x ordinal   to y ordinal   and return x or y correspondingly   You may need to re-order you values to make such comparison meaningful    If that is not possible  I would store MyEnum values   into a static array

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This not something that is usually done  so I would reconsider  But having said that  the fundamental operations are  int --  enum using EnumType values   intNum   and enum --  int using enumInst ordinal     However  since any implementation of values   has no choice but to give you a copy of the array  java arrays are never read-only   you would be better served using an EnumMap to cache the enum --  int mapping

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You can try like this  Create Class with element id          public Enum MyEnum           THIS 5           THAT 16           THE OTHER 35            private int id     Could be other data type besides int         private MyEnum int id                this id   id                     public static MyEnum fromId int id                    for  MyEnum type   values                          if  type getId      id                            return type                                                          return null                          Now Fetch this Enum using id as int   MyEnum myEnum   MyEnum fromId 5

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Use MyEnum enumValue   MyEnum values   x

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I cache the values and create a simple static access method   public static enum EnumAttributeType       ENUM 1      ENUM 2      private static EnumAttributeType   values   null      public static EnumAttributeType fromInt int i            if EnumAttributeType values    null                EnumAttributeType values   EnumAttributeType values                      return EnumAttributeType values i

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Wrote this implementation  It allows for missing values  negative values and keeps code consistent  The map is cached as well  Uses an interface and needs Java 8   Enum  public enum Command implements OrdinalEnum      PRINT FOO -7       PRINT BAR 6       PRINT BAZ 4        private int val      private Command int val           this val   val             public int getVal            return val             private static Map lt Integer  Command gt  map   OrdinalEnum getValues Command class       public static Command from int i           return map get i             Interface  public interface OrdinalEnum      public int getVal          SuppressWarnings  unchecked       static  lt E extends Enum lt E gt  gt  Map lt Integer  E gt  getValues Class lt E gt  clzz           Map lt Integer  E gt  m   new HashMap lt  gt             for Enum lt E gt  e   EnumSet allOf clzz               m put   OrdinalEnum e  getVal     E e            return m

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In case it helps others  the option I prefer  which is not listed here  uses Guava s Maps functionality   public enum MyEnum       OPTION 1 -66       OPTION 2 32        private int value      private MyEnum final int value            this value   value             public int getValue             return this value             private static ImmutableMap lt Integer  MyEnum gt  reverseLookup                Maps uniqueIndex Arrays asList MyEnum values      MyEnum  getValue        public static MyEnum fromInt final int id            return reverseLookup getOrDefault id  OPTION 1             With the default you can use null  you can throw IllegalArgumentException or your fromInt could return an Optional  whatever behavior you prefer

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Try MyEnum values   x  where x must be 0 or 1  i e  a valid ordinal for that enum    Note that in Java enums actually are classes  and enum values thus are objects  and thus you can t cast an int or even Integer to an enum

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Java enums don t have the same kind of enum-to-int mapping that they do in C     That said  all enums have a values method that returns an array of possible enum values  so  MyEnum enumValue   MyEnum values   x     should work  It s a little nasty and it might be better to not try and convert from ints to Enums  or vice versa  if possible

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Here s the solution I plan to go with   Not only does this work with non-sequential integers  but it should work with any other data type you may want to use as the underlying id for your enum values   public Enum MyEnum       THIS 5       THAT 16       THE OTHER 35        private int id     Could be other data type besides int     private MyEnum int id            this id   id             public int getId             return this id             public static Map lt Integer  MyEnum gt  buildMap             Map lt Integer  MyEnum gt  map   new HashMap lt Integer  MyEnum gt             MyEnum   values   MyEnum values            for  MyEnum value   values                map put value getId    value                      return map            I only need to convert id s to enums at specific times  when loading data from a file   so there s no reason for me to keep the Map in memory at all times   If you do need the map to be accessible at all times  you can always cache it as a static member of your Enum class

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MyEnum values   x  is an expensive operation  If the performance is a concern  you may want to do something like this   public enum MyEnum       EnumValue1      EnumValue2       public static MyEnum fromInteger int x            switch x            case 0              return EnumValue1          case 1              return EnumValue2                    return null

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This is the same answer as the doctors but it shows how to eliminate the problem with mutable arrays  If you use this kind of approach because of branch prediction first if will have very little to zero effect and whole code only calls mutable array values   function only once  As both variables are static they will not consume n   memory for every usage of this enumeration too   private static boolean arrayCreated   false  private static RFMsgType   ArrayOfValues   public static RFMsgType GetMsgTypeFromValue int MessageID        if  arrayCreated    false            ArrayOfValues   RFMsgType values               for  int i   0  i  lt  ArrayOfValues length  i              if  ArrayOfValues i  MessageIDValue    MessageID                return ArrayOfValues i                       return RFMsgType UNKNOWN

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Based on  ChadBefus  s answer and  shmosel comment  I d recommend using this    Efficient lookup  and works on pure java    8   import java util stream Collectors  import java util function Function  import java util Map  import java util Arrays   public enum MyEnum       OPTION 1 -66       OPTION 2 32        private int value      private MyEnum final int value            this value   value             public int getValue             return this value             private static Map lt Integer  MyEnum gt  reverseLookup           Arrays stream MyEnum values    collect Collectors toMap MyEnum  getValue  Function identity           public static MyEnum fromInt final int id            return reverseLookup getOrDefault id  OPTION 1             public static void main String   args            System out println fromInt -66  toString

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In Kotlin   enum class Status val id  Int        NEW 0   VISIT 1   IN WORK 2   FINISHED 3   CANCELLED 4   DUMMY 5        companion object           private val statuses   Status values   associateBy Status  id           fun getStatus id  Int   Status    statuses id            Usage   val status   Status getStatus 1

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If you want to give your integer values  you can use a structure like below  public enum A           B 0           C 10           None 11           int id          private A int i  id   i            public int GetID   return id           public boolean IsEmpty   return this equals A None            public boolean Compare int i  return id    i           public static A GetValue int  id                        A   As   A values                for int i   0  i  lt  As length  i                                  if As i  Compare  id                       return As i                             return A None

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You can iterate over values   of enum and compare integer value of enum with given id like below   public enum  TestEnum       None 0       Value1 1       Value2 2       Value3 3       Value4 4       Value5 5        private final int value      private TestEnum int value            this value   value             public int getValue             return value             public static TestEnum  getEnum int value           for  TestEnum e TestEnum values                  if e getValue      value                  return e                    return TestEnum None   For values out of enum scope           And use just like this  TestEnum x   TestEnum getEnum 4    Will return TestEnum Value4 I hope this helps

[java] Cast Int to enum in Java

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