Permutations in Java

Permutations.java

import java.util.Arrays;
import java.util.ArrayList;

public final class Permutations {

    private static final int input[] = {1, 2, 3};

    public static void main (String args[]) {
        // Permute
        ArrayList<int[]> permutations = permute(input);
        // Print
        for (int[] permutation : permutations) System.out.println(Arrays.toString(permutation));
    }

    private static ArrayList<int[]> permute (int[] numbers) {
        // Create the result collection
        ArrayList<int[]> result = new ArrayList<>();
        // Permute
        permute(result, new int[numbers.length], numbers, 0);
        // Return it
        return result;
    }

    private static void permute (ArrayList<int[]> result, int[] permutation, int[] numbers, int index) {
        // Get the value at the index
        int value = numbers[index];
        // Loop
        for (int i = 0; i < numbers.length; i++) {
            // Check that we can place this value in the spot
            if (permutation[i] != 0) continue;
            // Place the value there
            permutation[i] = value;
            // Permute
            if (index < numbers.length - 1) permute(result, permutation, numbers, index + 1);
            // If we are at the last index, then we have a result
            else result.add(permutation.clone());
            // Reset the value
            permutation[i] = 0;
        }
    }
}