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.
Is there a library function available in Java?
Apart from Collections.sort(list) which sorts the entire List!
Writing a highly optimised custom sort function will take some work.
In Java 8+, use List#sort.
list.subList(0,3).sort(null) ;
In earlier Java:
Collections.sort(list.subList(0,3));
Note: '3' here is excluded from sorting.
To quote 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.
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.
AbstractList" is not wrong, as such, it's mostly irrelevant. It's more important that subList is defined by List, in my opinion.
List does NOT define subList. Hence, the relevance of letting the OP know where exactly does ArrayList inherit that behaviour from.
List is an interface, so what I was merely implying is that it doesn't implement it, while AbstractList does.