整数配列の一意の順列をすべて生成するにはどうすればよいでしょうか?

int[] a = {3, 4, 6, 2, 1};

for (int i = 0; i < a.length; i++) {
  // Perform actions for each element of the array
  for (int j = i + 1; j < a.length; j++) {
    // Swap elements at indices i and j to generate a permutation
    int temp = a[i];
    a[i] = a[j];
    a[j] = temp;

    // Check if the current permutation has already been generated
    if (!hasBeenGenerated(a)) {
      // If the permutation is new, add it to the list of permutations
      addPermutationToList(a);
    }

    // Swap the elements back to restore the original array
    temp = a[i];
    a[i] = a[j];
    a[j] = temp;
  }
}