JAVA program to print all permutations of a string

ALGORITHM:

The permutation of a string is the rearrangement of the string in different orders to form different strings of the same length. A string of length n can have n! permutations.

Source: Mathworld

We will start with each letter of the string and then we found all the possible combinations for the string beginning with that letter. And once we picked a letter in the 2nd position, we then found all the possible combinations that begin with that 2 letter sequence before we changed any of the letters in the first 2 positions. So, basically what we did was choose a letter and then peformed the permutation process starting at the next position to the right before we come back and change the character on the left. 

CODE:

import java.util.Scanner;

public class permutations{
   
    static char[] swap(char[] a,int i,int j){
        char tmp =a[i];
        a[i]=a[j];
        a[j]=tmp;
        return a;
    }
   
    static void printArray(char[] a){
        for (int i=0;i<a.length;i++)
            System.out.print(a[i]);
        System.out.println();
    }

    static void permute(char[] a,int index){
        if(index==a.length){
            printArray(a);
            return;
        }
        for(int i=index;i<a.length;i++){
            a=swap(a,i,index);
            permute(a,index+1);
            a=swap(a,i,index);
        }
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.print("Enter the string: ");
        permute(in.next().toCharArray(),0);
    }
}

OUTPUT:

Enter the string: abc
abc
acb
bac
bca
cba
cab