Question

Please code in Java Write a recursive method that takes a string and return a string where every character appears twice. For example, if the string is “HELLO”, it will return “HHEELLOO”. Write a program to test it.

Answer 1

import java.util.Scanner;

public class DoubleCharacters {

    public static String repeatCharacters(String s) {
        if (s.length() == 0) {
            return "";
        } else if (s.length() == 1){
            return s + s;
        } else {
            if (s.charAt(0) == s.charAt(1)) {
                return s.substring(0, 2) + repeatCharacters(s.substring(2));
            } else {
                return "" + s.charAt(0) + s.charAt(0) + repeatCharacters(s.substring(1));
            }
        }
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.print("Enter a string: ");
        String s = in.nextLine();
        System.out.println(repeatCharacters(s));
    }
}