How to generate a random permutation in Java?

Question

What is the best way to generate a random permutation of n numbers?

For example, say I have a set of numbers 1, 2 and 3 (n = 3)

Set of all possible permutati

Answer 1

java.util.Collections.shuffle(List);

javadoc link for Collections.shuffle

List list = new ArrayList();
list.add(1);
list.add(2);
list.add(3);
java.util.Collections.shuffle(list);

It's worth noting that there are lots of algorithms you can use. Here is how it is implemented in the Sun JDK:

public static void shuffle(List list, Random rnd) {
    int size = list.size();
    if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
        for (int i=size; i>1; i--)
            swap(list, i-1, rnd.nextInt(i));
    } else {
        Object arr[] = list.toArray();

        // Shuffle array
        for (int i=size; i>1; i--)
            swap(arr, i-1, rnd.nextInt(i));

        // Dump array back into list
        ListIterator it = list.listIterator();
        for (int i=0; i