I need to know how to do this without using the StringBuilder answer = new StringBuilder()

6. Write a method doubleChars, that returns a String containing all chars in the received String two times in the returned String. method signature: public static String doubleChars(String str) doubleChars("The") returns "TThhee" // TT for T, hh for h, ee for e doubleChars("AAbb") returns "AAAAbbbb" doubleChars("Hi-There") returns "HHii--TThheerree" doubleChars("") returns doubleChars("") returns" !! 11