Java: Getting an array of ENUM elements

Question

Is there a better way of creating arrays from elements of an enum:

    public static enum LOGICAL {
        AND ("&", "AND"),
        OR ("||", "OR");

        public final String symbol;
        public final String label;

        LOGICAL(String symbol, String label) {
            this.symbol=symbol;
            this.label=label;
        }
    }

    public static final String[] LOGICAL_NAMES = new String[LOGICAL.values().length];
    static{
        for(int i=0; i<LOGICAL.values().length; i++)
            LOGICAL_NAMES[i]=LOGICAL.values()[i].symbol;
    }

    public static final String[] LOGICAL_LABELS = new String[LOGICAL.values().length];
    static{
        for(int i=0; i<LOGICAL.values().length; i++)
            LOGICAL_LABELS[i]=LOGICAL.values()[i].label;
    }

Jon Skeet · Accepted Answer · 2011-05-28 08:21:26Z

3

Personally I wouldn't expose them as an array, whose contents can be changed by anyone. I'd probably use an unmodifiable list instead - and probably expose that via a property rather than as a field. The initialization would be something like this:

private static final List<String> labels;
private static final List<String> values;

static
{
    List<String> mutableLabels = new ArrayList<String>();
    List<String> mutableValues = new ArrayList<String>();
    for (LOGICAL x : LOGICAL.values())
    {
         mutableLabels.add(x.label);
         mutableValues.add(x.value);
    }
    labels = Collections.unmodifiableList(mutableLabels);
    values = Collections.unmodifiableList(mutableValues);
}

(If you're already using Guava you might even want to use ImmutableList instead, and expose the collections that way to make it clear that they are immutable.)

answered May 28, 2011 at 8:21

Jon Skeet

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1 Comment

Alvin Over a year ago

Yes! I wish there is a ImmutableList in standard Java API.

Bozho · Accepted Answer · 2011-05-28 08:11:48Z

2

No. That seems the proper way. Even if there was some utility, it would rely on reflection

If you are using it often cache it in the enum

answered May 28, 2011 at 8:11

Bozho

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4 Comments

marcolopes Over a year ago

Please explain what do you mean by "caching". Move the static arrays to the enum body?

Bozho Over a year ago

Store it in a field so that you don't compute it everytime

marcolopes Over a year ago

I was convinced that this code would only run ONCE (on the first access to the class).

Bozho Over a year ago

ah, yes - I missed the constant definition. So you are already caching it.

ahmet alp balkan · Accepted Answer · 2011-05-28 08:27:10Z

2

If you use your values very frequently and your enumeration gets bigger use Maps. Declare the following in your class.

private static EnumMap<LOGICAL,String> symbols = new EnumMap<LOGICAL, String>(LOGICAL.class);

and then just below it:

static{
    for(LOGICAL i : LOGICAL.values().)
        symbols.put(i, i.symbol);
}

then you can use symbols.values() or symbols.get(LOGICAL.AND) etc.

answered May 28, 2011 at 8:27

ahmet alp balkan

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