Re: Passing enum and EnumMap to a method

Tom Hawtin <>
Tue, 15 May 2007 16:40:31 +0100
Tom Hawtin wrote:

The question didn't jump out at me, but I'm guessing you are asking how
to get all the elements of an enum given an EnumMap with the enum as the
key type.

AFAIK, the only guaranteed way to obtain the 'keyClass' that I can see
is through serialisation - not pleasant.

Ah, it seems that you can extract the full set of elements for the enum,
so long as you have a non-empty key-set. Of course if you have an
example element you can getClass, find the enum class and then all the
elements yourself.

import java.util.*;

class EnumMapToAllKeys {
     public static void main(String [] args) {
         Map<Thread.State, String> map =
             new EnumMap<Thread.State, String>(Thread.State.class);
         map.put(Thread.State.BLOCKED, "block");
         map.put(Thread.State.TIMED_WAITING, "timed");
      * @throws IllegalArgumentException if map is empty(!)
     private static <K extends Enum<K>> void print(Map<K, ?> map) {
         EnumSet<K> all = EnumSet.copyOf(map.keySet());
         for (K key : all) {
             System.out.println(key+" => "+map.get(key));

It would work properly if EnumSet.copyOf could extract the class
information from EnumMap.keySet. Perhaps an RFE (and patch) is in order
to add that sort of functionality across collections.

Tom Hawtin

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