Long[] to long[] and vice versa?

Question

Does anybody know an efficient, quick and clean way to convert Long[] to long[] and vice versa in Java outside the obvious for-loop with (un)box&copy?

Note: This is not about unboxing Long or boxing long. I am explicitly talking about arrays!

"There is no better way than loop and copy" would also be an answer ;)

EDIT: I am aware of the implications of doing the above and that it is better to avoid it. Just assume, I cannot avoid it and want to do it as smartly as possible without using 3rd party stuff.

"There is no better way than loop and copy" :) - Java is pretty rigid with its array types. 'Cast-style' conversions don't work and auto-unboxing does not work for arrays (yet?). — JimmyB, Dec 13 '12 at 12:32
An array of `Long` objects is completely different from an array of `long` primitives. There is no trick to convert them that's more efficient than looping and unboxing. — Jesper, Dec 13 '12 at 12:35

score 10 · Answer 1 · edited Dec 13 '12 at 12:41

10

If you use apache commons lang you can do:

long[] primitive = ArrayUtils.toPrimitive(new Long[]{1L, 2L, 3L, 4L});

edited Dec 13 '12 at 12:41

jakber

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answered Dec 13 '12 at 12:33

Polyana Fontes

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Neat answer, but I tend to not use 3rd party libs. – Fildor Dec 13 '12 at 12:43
This is not a good answer, it has no explanation and uses a loop. – durron597 Dec 13 '12 at 12:45
1

@durron597 - a loop is unavoidable. – Stephen C Dec 14 '12 at 11:54
@StephenC I know a loop is unavoidable, but because of the lack of explanation it's misleading to readers. – durron597 Dec 14 '12 at 13:01

score 8 · Accepted Answer · answered Dec 13 '12 at 12:33

8

There is no better way than loop and copy

The best solution is to avoid converting in the first place. If you are worries about efficiency avoid using Long[] as it is many times larger than long[] If you need to use a collection you can try TLongArrayList which wraps a long[].

answered Dec 13 '12 at 12:33

Peter Lawrey

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Prerequsite for asking the question in the first place was that I cannot avoid convertion for reasons that are out of my jurisdiction. I just thought that if I cannot avoid it, I at least want to do it as smart as possible. – Fildor Dec 13 '12 at 12:48

durron597 · Answer 3 · 2012-12-13T12:38:11.657

When Java boxes/unboxes, it actually DOES something, even if it doesn't show it to the user.

Long[] and long[] are very different objects. So the answer is, no, you have to loop and copy. But a better question is, why do you need this? You can use them interchangeably in almost any situation... You must decide at implementation what's more important to you, object creation, or memory usage. Hopefully you use Long.valueOf to create your Longs (or autoboxing) to use Java's caching for Long values.

This is the source of apache common lang's ArrayUtils.toPrimitive. It uses a loop.

public static long[] toPrimitive(Long[] array) {
  if (array == null) {
    return null;
  } else if (array.length == 0) {
    return EMPTY_LONG_ARRAY;
  }
  final long[] result = new long[array.length];
  for (int i = 0; i < array.length; i++) {
    result[i] = array[i].longValue();
  }
  return result;
}

score 1 · Answer 4 · answered Dec 13 '12 at 12:33

1

Java by itself does not provide any way to convert an array of objects to array of premitives.

answered Dec 13 '12 at 12:33

Swagatika

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Sajid Hussain · Answer 5 · 2012-12-13T12:36:10.620

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ArrayUtil ReferenceHope this may help.

long[] longs = new long[]{1L};
Long[] longObjects = ArrayUtils.toObject(longs);
List<Long> longList = java.util.Arrays.asList(longObjects);

edited Dec 13 '12 at 12:36

answered Dec 13 '12 at 12:33

Sajid Hussain

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score 1 · Answer 6 · answered Dec 13 '12 at 12:33

1

There is no better way than loop and copy, wrapped in a helper function that you can use over and over again.

answered Dec 13 '12 at 12:33

NPE

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score 0 · Answer 7 · edited May 23 '17 at 11:52

0

You can do it with ArrayUtils from apache as detailed here:

Convert an array of primitive longs into a List of Longs

edited May 23 '17 at 11:52

Community

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answered Dec 13 '12 at 12:33

nwaltham

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score 0 · Answer 8 · answered Jul 06 '22 at 18:08

0

I can see no one answered for vice versa i.e long[] to Long[], here is the simple technique, none other than looping !

 int index=0;
 long prim[]={2,100,12,1};
 Long obj[]=new Long[prim.length];
 for(long x:prim){
     res[index++]=x;
 }

answered Jul 06 '22 at 18:08

Rahul Khatoliya

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Long[] to long[] and vice versa?

8 Answers8