Re: Enum dictionary issue: will this work?

Roland de Ruiter <>
Thu, 21 Aug 2008 15:09:19 +0200
On 21-8-2008 14:35, Roland de Ruiter wrote:

On 21-8-2008 12:21, Ben Phillips wrote:

Here's the code. The enum constants should get added to a private map
with a public, unmodifiable view as they are created. It definitely
won't work if the map put is right in the constructor. Will this sort
of thing work as written, with a static method called that initializes
the map if it's null? Or will the map just get clobbered back to null
after the enum constants are all constructed? And if not, will the
unmodifiable view be constructed correctly?

When the enum class Thing loads and gets initialized, the following will
happen and in this order:


Order according to the Java Language Specification, see

Personally I would have written it differently, e.g. like the class below.

Since the thingMap is only an auxiliary object, I don't think it
shouldn't be a field of the enum class. Using the values() method, the
"things" map can easily be created after all enum constants have been

import java.util.*

public enum Thing {

    public static final Map<String, Thing> things = createThings();

    private String name;

    private Thing(String name) { = name;

    private static Map<String, Thing> createThings() {
       Map<String, Thing> thingMap = new HashMap<String, Thing>();
       for (Thing thing : values()) {
          thingMap.put(, thing);
       return Collections.unmodifiableMap(thingMap);

    public static void main(String[] args) {



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