Re: Java 5.0 Enum: why not valueOf(int ordinal)?

diegomrosa wrote: 
If you had stored information on the enum based on the ordinal (say
writing ordinal values to a file for later rereading) then these values
would correspond to the wrong enums when reloaded.  On the other hand,
had you used the string values, all would be well.  If you *know* that
your enum is never going to change, using the ordinal may be suitable.
If you do have to add values later, just make sure to put them at the
end.



maybe the right question would be: "how to safely/efficiently store
enum values?". Well, I dont know about the rest of you, but I need to
persist enum values all the time!

The obvious way to store an enum value seems to be using its ordinal
(at least to me!). Storing the string values would be a lot more
expensive and not a bit more secure. You are right in saying that
storing the ordinal could be dangerous in case you change the enum
order. However, storing the string value would prohibit the user
changing the name of the enum constants. Both cases seem remote to me,
but I would consider changing a enum value name even more common than
changing its order. That is why my surprise that class Enum has a
method to convert a string into an enum but not an equivalent to
convert an ordinal into an enum.

Ok, I can write a method somewhere to convert an ordinal into an enum,
but where should I put it?!? Well, the Enum class seems to be the
obvious choice.


If you are sure your enum won't change, or that values will only be
added to the end, then a static method such as:

enum Ints {
   ZERO,ONE,TWO,THREE,FOUR;

   public static Ints fromOrd(int i) {
       if (i < 0 || i >= Ints.values().length) {
           throw IndexOutOfBoundsException("Invalid ordinal");
       }
       return Ints.values()[i];
   }
}



this means I have to duplicate this code on every Enum. Frustrating!


might work.  Alternatively you can build you own ordinal system that
can use values you define, although it's a bit of a PITA:

enum Ints {
   ZERO(0),
   ONE(1),
   TWO(2),
   THREE(3),
   FOUR(4);

   private final int _ord;

   Ints(int i) {
       _ord = i;
   }

   int getOrd() { return _ord; }
}



More frustrating!

Diego

Heinz wrote a good article on this.  If you haven't read his
newsletters yet, there very good.

http://www.javaspecialists.co.za/archive/Issue113.html
.

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