Re: enum or array ?

Mark Space <>
Fri, 29 May 2009 15:31:21 -0700
Mike Schilling wrote:

That's true. But it's quite possible (i.e. I've done it) to build a
class that mimics the code generated for Enums while allowing both
predefined values (which get static instances generated for them) plus

This is a good point. For the OP, I think what Mike is saying is
something like this:

public class Currency {

   public final static Currency US = new Currency("US");
   public final static Currency EUR = new Currency("EUR");
   public final static Currency YUAN = new Currency("YUAN");

   private String name;

   private Currency( String name ) { = name;

This works almost exactly like the enum the OP proposed. It's accessed
like an enum (Currency.US) and you can't extend it (because of the
private constructor). I think that an enum in Java is pretty much
boilerplate for the above pattern.

The above code has the advantage that you can add a public constructor
and then get an extensible class.

values added at runtime (which do not.) (In fact, since the Java
code for such a class is boilerplate, I've built a tool to generate
it.) You still get many of the advantages of enums, but not all: e.g.
you can't switch on them, nor can you override methods per-value.

I'm thinking something like this. What's your pattern?

public class Currency {

   private final static Currency[] defaults =
       new Currency("US"),
       new Currency("EUR"),
       new Currency("YUAN"),

   private String name;
   private static CopyOnWriteArraySet<Currency> currencies;
      currencies = new CopyOnWriteArraySet( Arrays.asList(defaults) );

   protected Currency( String name ) { = name;

   public void addCurrencies( Currency[] c ) {
     currencies.addAll( Arrays.asList(c) );

  public Set<Currency> getCurrencies() {
    return Collections.unmodifiableSet( currencies );

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