Re: Better way to implement reverse mapping of custom enum ordinals?

Tom Anderson <>
Sat, 19 Dec 2009 13:25:24 +0000
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On Fri, 18 Dec 2009, John B. Matthews wrote:

In article
"david.karr" <> wrote:

On Dec 18, 4:25??pm, EJP <> wrote:

david.karr wrote:

Can someone think of a better way to do this, that doesn't repeat
the column values?

Have each enum value enter itself on construction into a
Map<Integer, YourEnum> with its own ColumnValue as the key.

Concerning the Map, I had already thought of that. That's the obvious
way to do it. Now, how would you do it? I would assume you'd define a
static Map in the enum type and have the constructor put itself into
the map. The problem is, it doesn't appear to be possible to do that.
It doesn't compile.

A static initializer works, as suggested in the "enum Color" discussion:


You can also trick the constructor-put idea into working by moving the map
into a different class, which can even be an inner class of the enum:

public enum SomeType {

  private static class ByColumnValue {
  public static final Map<Integer, SomeType> MAP = new HashMap<Integer, SomeType>();

  private final int columnValue;

  private SomeType(int columnValue) {
  this.columnValue = columnValue;
  ByColumnValue.MAP.put(columnValue, this);

  public SomeType getEnum(int columnValue) {
  return ByColumnValue.MAP.get(columnValue);


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