长 [] 到长 [] 反之亦然？

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.

Answer 1

如果您使用apache commons lang ，您可以执行以下操作：

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

Answer 2

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[].

Answer 3

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 Long s (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;
}

Answer 4

Java 本身不提供将对象数组转换为预置数组的任何方法。

Answer 5

ArrayUtil Reference Hope this may help.

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

Answer 6

没有比循环和复制更好的方法了，包裹在一个可以反复使用的辅助函数中。

Answer 7

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

Convert an array of primitive longs into a List of Longs

Answer 8

I can see no one answered for vice versa ie 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;
 }