Variations

package com.company;
public class Main {
    static int a = 3;
    static int b = 4;
    static int[] mainArr = new int[a];
    static int[] tempArr = new int[]{1, 2, 3, 4};
    public static void main(String[] args) {
        Gen(0);
        Swap(a, b);
    }
    private static void Gen(int index) {
        if (index >= a){
            Print();
        }else {
        for (int i = index; i < b; i++) {
            mainArr[index] = tempArr[i];
            Swap(tempArr[i], tempArr[index]);
            Gen(index + 1);
            Swap(tempArr[i], tempArr[index]);
        }
        }
    }
    static void Swap(int ind1, int ind2){
        int temp = ind1;
        ind1 = ind2;
        ind2 = temp;
    }
    static void Print(){
        for (int i : mainArr) {
            System.out.print(i + " ");
        }
        System.out.println();
    }
}