public class Recursion {

public static void main(String[] args){

//problem1:Print a string in reverse order.

String first = "first program";

//printStringInReverse(first);

printReverse("xyzabc".toCharArray());

}

private static void printStringInReverse(String str) {

if (str == null || str.isEmpty()) return;

//System.out.println(str.substring(1));

printStringInReverse(str.substring(1));

System.out.print(str.charAt(0));

}

private static void printReverse(char [] str) {

helper(0, str);

}

private static void helper(int index, char [] str) {

if (str == null || index >= str.length) {

return;

}//xyzabc

System.out.println(str[index] + " " + index);

helper(index + 1, str);

System.out.print(str[index]);

}

}