Sorting a part of Java ArrayList

Question

What is the most efficient way of sorting only a part of ArrayList? Say all elements from index 0 to 3 in an Arraylist which contains 10 elements.

Answer 1

Collections.sort(list.subList(0,3));

Note: '3' here is excluded from sorting

It is described in the documentation:

public List subList(int fromIndex, int toIndex)

Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive.

Answer 2

use the subList [inherited from AbstractList] method in ArrayList. And then use Collections.sort() on that sub-list. That is if writing a highly optimised custom sort function is truly hard work.