Generate non-repetetive permutations of given numbers and utilize each combination. Example result for 4: 4! = 24 combinations

Permutations.java

import java.util.*;

class Permutations {

    public static void main(final String[] args) {
        // Permutations of the numbers 0 to 3 to get all possible combinations.
        // For 4 numbers the result should be 4! = 24 different combinations
        // like 1-2-3-4, 1-2-4-3, 1-3-2-4, 1-3-4-2, etc.
        Collection<List<Integer>> permutations = new Permutations()
                .generatePermutationsWithoutRepetition(new HashSet<>(Arrays.asList(0, 1, 2, 3)));

        permutations.forEach(perm -> {
            System.out.println(perm.get(0));
            System.out.println(perm.get(1));
            System.out.println(perm.get(2));
            System.out.println(perm.get(3));
        });
    }

    public <T> Collection<List<T>> generatePermutationsWithoutRepetition(Set<T> availableNumbers) {
        Collection<List<T>> permutations = new HashSet<>();

        for (T number : availableNumbers) {
            Set<T> numbers = new HashSet<>(availableNumbers);
            numbers.remove(number);

            if (!numbers.isEmpty()) {
                Collection<List<T>> childPermutations = generatePermutationsWithoutRepetition(numbers);
                for (List<T> childPermutation : childPermutations) {
                    List<T> permutation = new ArrayList<>();
                    permutation.add(number);
                    permutation.addAll(childPermutation);
                    permutations.add(permutation);
                }
            } else {
                List<T> permutation = new ArrayList<>();
                permutation.add(number);
                permutations.add(permutation);
            }
        }

        return permutations;
    }
}