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From: Lew <lewbloch@gmail.com>
Newsgroups: comp.lang.java.help
Subject: Re: Dynamic enums
Date: Tue, 11 Oct 2011 19:03:46 -0700 (PDT)
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Linus Flustillbe wrote:
> Let's say I have an ENUM defined as
> 
> public enum xxx {
>   A, B, C, D, E
> }
> 
> Now here's my question.
> Let's say I have a table called foobar which has the following rows
> 
> A  1
> B  2
> C  3
> D  4
> E  5
> 
> My code is written and is working great.  The enum xxx is used as a
> lookup on the foobar table.  If I add a row to foobar like
> 
> F  6
> 
> I need to add another enum to the xxx enum and rebuild my project.
> 
> So my question is, is there something like a dynamic enun:  by this
> could I call a method on the xxx enum like
> 
> xxx.addnew("F") that would make F a valid enum of xxx and not have to
> rebuild my project?

You can do it, though I don't have the patience to go into a whole lot of detail just now.  You have to sacrifice the built-in conveniences that 'enum' enjoys as a special part of the language, in favor of the flexibility you require.

You write a "type-safe enumeration" class of your own.  At a minimum you should support a 'fromString()' and 'toString()' method similar to real enums' 'valueOf()' and 'toString()'.

/Effective Java/, first edition, had a chapter on this that might by googlable.  The book itself is in the second edition and that chapter was removed due to the presence of enums in 5 and on.

Essentially you create static immutable instances of your custom class and use a private (or package-private) constructor.

-- 
Lew