Re: Random Enum

From:

markspace <nospam@nowhere.com>

Newsgroups:

comp.lang.java.help

Date:

Tue, 25 Aug 2009 09:39:21 -0700

Message-ID:

<h7143t$hec$1@news.eternal-september.org>

Roedy Green wrote:

On Mon, 24 Aug 2009 16:32:09 -0700, markspace <nospam@nowhere.com>
wrote, quoted or indirectly quoted someone who said :

static Enum<?> randomEnum( Enum<?> e )
    {
        return random( e.getDeclaringClass() );
    }

    private static final Random rand = new Random();

    public static <E extends Enum<E>> E random( Class<E> clazz )
    {
        E[] values = clazz.getEnumConstants();
        return values[rand.nextInt( values.length )];
    }

Two questions that may be of interest to the general audience.

1. What happens if you do simply "e.values()", rather than the
roundabout "getDeclaringClass" and "getEnumConstants"?

e.values() won't even compile. It's a static method declared on
subclasses of Enum, not Enum itself.

2. how do you get away with "E[] values"? Seems to me arrays and
generics are like trying to get oil and water to mix.
What type is getEnumConstants actually returning at run time?

T[] always works fine. It's trying to declare a "new" array where you
get into trouble (and then only a bit, unless you don't know what the
tricks are).

You really ought to get Effective Java by Joshua Bloch, Roedy. It goes
into this stuff and provides some excellent solutions.