Convert integer value to matching Java Enum

Question

I ve an enum like this   public enum PcapLinkType     DLT NULL 0    DLT EN10MB 1    DLT EN3MB 2     DLT AX25 3       snip  200 more enums  not always consecutive      DLT UNKNOWN -1       private final int value          PcapLinkType int value            this value  value            Now I get an int from external input and want the matching input - throwing an exception if a  value does not exist is ok  but preferably I d have it be DLT UNKNOWN  in that case   int val   in readInt    PcapLinkType type          convert val to a PcapLinkType

User · Answer

You will have to make a new static method where you iterate PcapLinkType.values() and compare:

public static PcapLinkType forCode(int code) {
    for (PcapLinkType typ? : PcapLinkType.values()) {
        if (type.getValue() == code) {
            return type;
        }
    }
    return null;
 }

That would be fine if it is called rarely. If it is called frequently, then look at the Map optimization suggested by others.

User · Answer

You would need to do this manually  by adding a a static map in the class that maps Integers to enums  such as  private static final Map lt Integer  PcapLinkType gt  intToTypeMap   new HashMap lt Integer  PcapLinkType gt     static       for  PcapLinkType type   PcapLinkType values              intToTypeMap put type value  type            public static PcapLinkType fromInt int i        PcapLinkType type   intToTypeMap get Integer valueOf i        if  type    null           return PcapLinkType DLT UNKNOWN      return type

User · Answer

There is no way to elegantly handle integer-based enumerated types  You might think of using a string-based enumeration instead of your solution  Not a preferred way all the times  but it still exists   public enum Port              The default port for the push server          DEFAULT  443                The alternative port that can be used to bypass firewall checks      made to the default  lt i gt HTTPS lt  i gt  port          ALTERNATIVE  2197       private final String portString     Port final String portString        this portString   portString                  Returns the port for given   link Port  enumeration value        return The port of the push server host          public Integer toInteger         return Integer parseInt portString

User · Answer

As  MeBigFatGuy says  except you can make your static       block use a loop over the values   collection   static       for  PcapLinkType type   PcapLinkType values              intToTypeMap put type getValue    type

User · Answer

This is what I use   public enum Quality  ENOUGH BETTER BEST                       private static final int amount   EnumSet allOf Quality class  size                         private static Quality   val   new Quality amount                        static  for Quality q EnumSet allOf Quality class    val q ordinal    q                           public static Quality fromInt int i    return val i                          public Quality next     return fromInt  ordinal   1  amount

User · Answer

if you have enum like this   public enum PcapLinkType     DLT NULL 0    DLT EN10MB 1    DLT EN3MB 2     DLT AX25 3     DLT UNKNOWN -1        private final int value          PcapLinkType int value            this value  value            then you can use it like  PcapLinkType type   PcapLinkType values   1     convert val to a PcapLinkType

User · Answer

static final PcapLinkType   values      DLT NULL  DLT EN10MB  DLT EN3MB  null                public static PcapLinkType  getPcapLinkTypeForInt int num           try             return values int            catch ArrayIndexOutOfBoundsException e              return DLT UKNOWN

User · Answer

I know this question is a few years old  but as Java 8 has  in the meantime  brought us Optional  I thought I d offer up a solution using it  and Stream and Collectors    public enum PcapLinkType     DLT NULL 0     DLT EN3MB 2     DLT AX25 3       snip  200 more enums  not always consecutive         DLT UNKNOWN -1       lt --- NO LONGER NEEDED    private final int value    private PcapLinkType int value    this value   value       private static final Map lt Integer  PcapLinkType gt  map    static       map   Arrays stream values             collect Collectors toMap e - gt  e value  e - gt  e           public static Optional lt PcapLinkType gt  fromInt int value        return Optional ofNullable map get value            Optional is like null  it represents a case when there is no  valid  value  But it is a more type-safe alternative to null or a default value such as DLT UNKNOWN because you could forget to check for the null or DLT UNKNOWN cases  They are both valid PcapLinkType values  In contrast  you cannot assign an Optional lt PcapLinkType gt  value to a variable of type PcapLinkType  Optional makes you check for a valid value first   Of course  if you want to retain DLT UNKNOWN for backward compatibility or whatever other reason  you can still use Optional even in that case  using orElse   to specify it as the default value   public enum PcapLinkType     DLT NULL 0     DLT EN3MB 2     DLT AX25 3       snip  200 more enums  not always consecutive      DLT UNKNOWN -1      private final int value    private PcapLinkType int value    this value   value       private static final Map lt Integer  PcapLinkType gt  map    static       map   Arrays stream values             collect Collectors toMap e - gt  e value  e - gt  e           public static PcapLinkType fromInt int value        return Optional ofNullable map get value   orElse DLT UNKNOWN

User · Answer

You could add a static method in your enum that accepts an int as a parameter and returns a PcapLinkType   public static PcapLinkType of int linkType         switch  linkType            case -1  return DLT UNKNOWN         case 0  return DLT NULL             ETC              default  return null

User · Answer

There s a static method values   which is documented  but not where you d expect it  http   docs oracle com javase tutorial java javaOO enum html  enum MyEnum       FIRST  SECOND  THIRD      private static MyEnum   allValues   values        public static MyEnum fromOrdinal int n   return allValues n        In principle  you can use just values   i   but there are rumors that values   will create a copy of the array each time it is invoked

User · Answer

You can do something like this to automatically register them all into a collection with which to then easily convert the integers to the corresponding enum   BTW  adding them to the map in the enum constructor is not allowed  It s nice to learn new things even after many years of using Java      public enum PcapLinkType       DLT NULL 0       DLT EN10MB 1       DLT EN3MB 2       DLT AX25 3         snip  200 more enums  not always consecutive        DLT UNKNOWN -1        private static final Map lt Integer  PcapLinkType gt  typesByValue   new HashMap lt Integer  PcapLinkType gt          static           for  PcapLinkType type   PcapLinkType values                  typesByValue put type value  type                        private final int value       private PcapLinkType int value            this value   value             public static PcapLinkType forValue int value            return typesByValue get value

[java] Convert integer value to matching Java Enum

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