Java "enum" : can you use non-consecutive ordinal numbers ?

[Sol Mayer-Orn]

Hi,

When using java "enum" , can I ask java to assign my own specific ordinals, instead of the default consecuitive values ?

For example, say I have the following ACTION codes (I can't control the code
values because they're taken from some legacy system):
* DELETE = 2;
* ADD = 5;
* EDIT =7;

I couldn't find any 'enum' tutorial which deals with it...
I could only find examples in the lines of:

   public enum ActionCodes{
      DELETE,   // java assigns ordinal '0', but i'd like it to be code '2'
      ADD,      // java assigns ordinal '1', but i'd like it to be '5'
      EDIT      // java assigns ordinal '2', but i'd like it to be '7'
   }

Any way to get the correct codes ?
Thanks !

[Jesper de Jong]

I haven't used Java enums much, but I don't think you can assign your own ordinals to enum constants.

However, enums in Java are quite flexible, they behave as a special kind of class. You could do this, for example:

public enum ActionCodes {
    DELETE(2),
    ADD(5),
    EDIT(7);
 
    private int code;
 
    private ActionCodes(int code) {
        this.code = code;
    }
 
    public int getCode() {
        return code;
    }
}

Then you can use for example DELETE.getCode() to get the value 2 which should be associated with the DELETE enum value.
[ September 19, 2007: Message edited by: Jesper Young ]

[Sol Mayer-Orn]

Thanks very much

[Nicholas Jordan]

[Jesper Young:]I haven't used Java enums much, but I don't think you can assign your own ordinals to enum constants.

Nor did I, and never really got the hang of it.

I just got used to static final, but your response may deprive the poster of needed design avenues:

public enum Planet {
    MERCURY (3.303e+23, 2.4397e6),
    VENUS   (4.869e+24, 6.0518e6),
    EARTH   (5.976e+24, 6.37814e6),
    MARS    (6.421e+23, 3.3972e6),
    JUPITER (1.9e+27,   7.1492e7),
    SATURN  (5.688e+26, 6.0268e7),
    URANUS  (8.686e+25, 2.5559e7),
    NEPTUNE (1.024e+26, 2.4746e7),
    PLUTO   (1.27e+22,  1.137e6);

At: Enums on the Java server.

[Sol Mayer-Orn]

Thanks very much, Nicholas Jordan, for your reply.

But could I please ask what's the difference between the design approach in your example (e.g. MERCURY (3.303e+23, 2.4397e6)) and the design approach in Jesper Young's reply (e.g. DELETE(2)) ?
I mean, don't they both reflect the idea of adding fields to your enum, and initializing them in the private constructor ?

Or did you mean to emphasize that additional fields can be 'double' and not just limited to 'int' ?

Thanks very much

[Nicholas Jordan]

I meant tp emphasize that additional fields can be added and other things that may be overlooked should be investigated before making further design decisions. I never really got going on enums when they seemed to be critical path selectors placed early in executable files where the runtime, in other languages, would switch on two byte or one byte values early in the loadable program that we in userland can see as a filename in a directory listing under the explorer interface.

Therefore, I just quit using them.

I was trying to draw attention that the decision needed further attention, nothing else beyond that.

Message edit: see the discussion I wanted to acheive by visiting the link:

http://java.sun.com/j2se/1.5.0/docs/guide/language/enums.html

right next to the smiley.
[ September 23, 2007: Message edited by: Nicholas Jordan ]

[Sol Mayer-Orn]

Thanks for this clarification.
And extra thanks for taking the time to reply in such detail

In my case, Jesper Young's reply did the job just great, just what I've been looking for.
But I agree that in general, it's very important to investigate as many options and alternatives as possible.