code: private boolean isLetter(final char paramInput) {
  
          return (paramInput >= '0' && paramInput <= '9') || (paramInput >= 'a' && paramInput <= 'z')
              || (paramInput >= 'A' && paramInput <= 'Z') || (paramInput == '_') || (paramInput == '-')
              || (paramInput == '.');
  
      }
docs: Checks if the given character is a letter.
  
  @param paramInput
  The character to check.
  @return Returns true, if the character is a letter.