code: public static String getLetters(String value) {
  
      StringBuilder letters = new StringBuilder(value.length());
  
      for (char chr : value.toCharArray()) {
        if (Character.isLetter(chr)) {
          letters.append(chr);
        }
      }
  
      return letters.toString();
    }
docs: Extracts letters from the String value.
  
  @param value the String value from which to extract letters.
  @return only letters from the String value.
  @throws NullPointerException if the String value is null.
  @see java.lang.Character#isLetter(char)