The best way to transform int[] to List<Integer> in Java? [duplicate]

Question

Possible Duplicate:
How to create ArrayList (ArrayList<T>) from array (T[]) in Java

How to implement this method:

List<Integer> toList(int[] integers) {     ???     //return Arrays.asList(integers); doesn't work } 

Answer 1

There's probably a built-in method to do it somewhere* (as you note, Arrays.asList won't work as it expects an Integer[] rather than an int[]).

I don't know the Java libraries well enough to tell you where that is. But writing your own is quite simple:

public static List<Integer> createList(int[] array) {     List<Integer> list = new ArrayList<Integer>(array.length);     for (int i = 0; i < array.length; ++i) {         list.add(array[i]);     }     return list; } 

Obviously one downside of this is that you can't do it generically. You'll have to write a separate createList method for each autoboxed primitive type you want.

_{*And if there isn't, I really wonder why not.}

Answer 2

Use commons-lang3 org.apache.commons.lang3.ArrayUtils.toObject(<yout int array>) and then java.util.Arrays.asList(<>)

ArrayUtils.toObject() will copy the array, and Array.asList() will simply create list that is backed by new array.

int[] a = {1, 2, 3}; List<Integer> aI = Arrays.asList(ArrayUtils.toObject(a)); 

EDIT: This wont work if you want to add() new elements (resize) though the list interface, if you want to be able to add new elements, you can use new ArrayList(), but this will create one more copy.