/**
  * Handles a character input.
  *
  * @param c the character being typed
  * @return {@code true} if the event was handled
  */
 public boolean handleChar(char c) {
   if (isValidCharacter(c)) {
     String str = String.valueOf(c);
     appendDisplayedText(str);
     commands.string(str);
     return true;
   }
   return false;
 }