Comparing two shuffling methods

Question

I'm trying to randomly shuffle an collection of integers within a List and I have came up with two shuffling method that does the job. However, I'm not sure which one works better. Does any one have any comments or suggestions?

public class TheCollectionInterface {
 public static <E> void swap(List<E> list1, int i, int j){
 E temp = list1.get(i);
 list1.set(i, list1.get(j));
 list1.set(j, temp);
 }
//alternative version 
// public static void shuffling(List<?> list, Random rnd){
// for(int i = list.size(); i >= 1; i--){
// swap(list, i - 1, rnd.nextInt(i));
// }
// }
 public static <E> void shuffling(List<E> list1, Random rnd){
 for(int i = list1.size(); i >= 1; i--){
 swap(list1, i - 1, rnd.nextInt(list1.size()));
 }
 }
 public static void main(String[] args) {
 List<Integer> li2 = Arrays.asList(1,2,3,4,5,6,7,8,9);
 Random r1 = new Random();
 TheCollectionInterface.shuffling(li2, r1);
 System.out.println(li2);
 }
}

• Legato: Did you consider Collections.shuffle()?
• Thor: yes, that's another alternative, but I just want to come up with a shuffling method myself, practice with the logic :)

Answer 1

Your algorithm doesn't have simple uniform distribution over !n. Your alternative do has it, is actually a known algorithm named Fisher–Yates shuffle.

• Thor: Thank you very much for the comment! Could you please explain in a bit more detail why my algorithm doesn't have simple uniform distribution over !n?