Mind blowing Permutations and Combinations in Java

This marvelous code is implemented and provided by "Riya Tyagi" from Galgotias College, Greater Noida. 


Note : Save this code inside Combinations.java file inside Eclipse IDE

import java.util.Scanner;

public class Combinations 
{
// method to find factorial of number
static int factorial(int num) 
{
if (num == 0)
return 1;
return num * factorial(num - 1);
}

// recursive method to find all permutations of given string
static String[] permutations(String x) 
{
String[] a;

// base case to stop the recursion
if (x.length() >= 1) 
               {
a = new String[factorial(x.length())];

int k = 0;

for (int i = 0; i < x.length(); i++) 
{
String[] b;

if (i > 0) 
{
                                       String t = x.substring(0, i).
                                                       concat(x.substring(i + 1, x.length()));

                                b = permutations(t); // call this method recursively 

} 

else 
{
String t = x.substring(1, x.length());
b = permutations(t);
}

for (int j = 0; j < b.length; j++) 
{
a[k] = String.valueOf(x.charAt(i)).concat(b[j]);
k++;
}

}  // end of for loop

}  // end of if

else 
{
a = new String[1];
a[0] = "";
}

return a;
}

public static void main(String[] args) 
{

Scanner sc = new Scanner(System.in);

  System.out.println("Input a string for its combinations: ");
String x = sc.next();

System.out.println("# output #");

String[] a = Combinations.permutations(x);

for (int i = 0; i < a.length; i++) 
{
System.out.println((i + 1) + " : " + a[i]);
}

} // end of main method

} // end of class