How do I concatenate static string arrays

Question

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How to concatenate two arrays in Java?

I have SET1 declared as a static String[] and I would like to declare SET2 as SET1 + few other parameters. Is it possible to declare SET2 statically similar (i.e. private static String[]) to SET1 but using the above definition, if not how to do this?

private static final String[] SET1 = { "1", "2", "3" };

SET2 = SET1 + { "4", "5", "6" };

Noel M · Accepted Answer · 2010-09-20T10:32:30.317

3

Look at Commons Util ArrayUtils.add:

static String[] SET2 = ArrayUtils.add(SET1, {"4", "5", "6" });

edited Sep 20 '10 at 10:32

answered Sep 20 '10 at 10:27

Noel M

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I guess we need to use Object[] and use addAll instead and casting it back to String[] – user339108 Sep 20 '10 at 10:39
I hope it doesn't clone when there are 2 sets of finite arguments. ArrayUtils.addAll(["a", "b", "c"], ["1", "2", "3"]) = ["a", "b", "c", "1", "2", "3"]. Cloning seems to be redundant here. – user339108 Sep 20 '10 at 10:40

score 2 · Answer 2 · answered Sep 20 '10 at 10:34

Maybe lists are easier in this case since arrays are fixed in length (by nature). You could do something like this if you want to instantiate it statically.

private static final List<String> SET1 = new ArrayList<String>();
private static final List<String> SET2 = new ArrayList<String>();
static {
    SET1.add("1");
    SET1.add("2");
    SET2.addAll(SET1);
    SET2.add("3");
}

Or use some kind of Collection utility library.

score 0 · Answer 3 · answered Sep 20 '10 at 10:39

It's a big ugly:

private static final String[] SET1 = { "1", "2", "3" };
private static final String[] SET2 = concat(
    String.class, SET1, new String[]{"4", "5", "6"});

@SuppressWarnings("unchecked")
static <T> T[] concat(Class<T> clazz, T[] A, T[] B) {
    T[] C= (T[]) Array.newInstance(clazz, A.length+B.length);
    System.arraycopy(A, 0, C, 0, A.length);
    System.arraycopy(B, 0, C, A.length, B.length);
    return C;
 }

score 0 · Answer 4 · answered Sep 20 '10 at 10:44

private static final String[] SET1 = { "1", "2", "3" };
private static final String[] SET2;

static
{
    List<String> set2 = new ArrayList<String>(Arrays.asList(SET1));
    set2.addAll(Arrays.asList("3", "4", "5"));
    SET2 = set2.toArray(new String[0]);
}

How do I concatenate static string arrays

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