public boolean isPalindrome()
{
  int length = text.length();

  // Separate case for shortest strings.
  if (length <= 1) return true;

  // Get first and last characters, converted to lowercase.
  char first = Character.toLowerCase(text.charAt(0));
  char last = Character.toLowerCase(text.charAt(length - 1));

  if (Character.isLetter(first) && Character.isLetter(last))
  {
    // Both are letters.
    if (first == last)
    {
      // Remove both first and last character.
      Sentence shorter = new Sentence(text.substring(1, length - 1));
      return shorter.isPalindrome();
    }
    else
      return false;
    }
    else if (!Character.isLetter(last))
    {
      // Remove last character.
      Sentence shorter = new Sentence(text.substring(0, length - 1));
      return shorter.isPalindrome();
    }
    else
    {
      // Remove first character.
      Sentence shorter = new Sentence(text.substring(1));
      return shorter.isPalindrome();
    }
}