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 consecu         


        

Answer 1

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

public static PcapLinkType forCode(int code) {
    for (PcapLinkType typе : 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.

Answer 2

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<Integer, PcapLinkType> intToTypeMap = new HashMap<Integer, PcapLinkType>();
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;
}

Answer 3

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.

Answer 4

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 */

Answer 5

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);
    }
}