code: private static String replaceCharAt(String s, int pos, char c) {
  		return s.substring(0, pos) + c + s.substring(pos + 1);
  	}
docs: Replaces a char in a String
  
  @param s
  The input string
  @param pos
  The position of the char to be replaced
  @param c
  The new char
  @return The new String
  @see Source: http://www.rgagnon.com/javadetails/java-0030.html