Array to List or List to Array, which conversion is faster?

Question

In java, basically these two conversions are so common and popular...

• Array to List

  List<String> list = Arrays.asList(array);

• List to Array

  String[] array = list.toArray(new String[list.size()]);

So the question is, which is faster, Array to List or its reverse?

Now, Why am I asking this question? Because I've to implement a method in which an array or a list, both can be passed in parameter. I just have to iterate this list and that's all. So here I have to decide that what should I convert? array to list or list to array!

Answer 1

Arrays.asList is faster because it does not copy data - it returns an object wrapping the array passed to it, and implementing the List interface. Collection.toArray() copies the data to the array, so it runs in O(N) instead of O(1).

Answer 2

Arrays.asList will faster since it doesnt have to copy any data instead it has to just pack it.