Strip phone number formatting

PhoneConverter.java

 /**
   * removes any non-digit character from the phone number
   * @param phoneNumber number to be de-formatted
   * @return phone number digits
   */
  protected String clearFormatting(String phoneNumber)
  {
    StringBuilder out = new StringBuilder(phoneNumber.length());    
    int lower = ((int)'0'-1);
    int upper = ((int)'9'+1);
    for (char c : phoneNumber.toCharArray() )
    { //only collect the digits
      if ( lower < c && upper > c ) { out.append(c); }
    }
    return out.toString();
  }