public class Palindromes
{
   public static void main(String[] args)
   {
      String sentence1 = "Madam, I'm Adam!";      
      System.out.println(sentence1);
      System.out.println("Palindrome: " + isPalindrome(sentence1));
      String sentence2 = "Sir, I'm Eve!";      
      System.out.println(sentence2);
      System.out.println("Palindrome: " + isPalindrome(sentence2));
   }

   /**
      Tests whether a text is a palindrome.
      @param text a string that is being checked
      @return true if text is a palindrome, false otherwise
   */
   public static boolean isPalindrome(String text)
   {
      return isPalindrome(text, 0, text.length() - 1);      
   }

   /**
      Tests whether a substring is a palindrome.
      @param text a string that is being checked
      @param start the index of the first character of the substring
      @param end the index of the last character of the substring
      @return true if the substring is a palindrome
   */
   public static boolean isPalindrome(String text, int start, int end)
   {
      // Separate case for substrings of length 0 and 1.
      if (start >= end) { return true; }
      else
      {
         // Get first and last characters, converted to lowercase.
         char first = Character.toLowerCase(text.charAt(start));
         char last = Character.toLowerCase(text.charAt(end));
         if (Character.isLetter(first) && Character.isLetter(last))
         {
            if (first == last)
            {
               // Test substring that doesn’t contain the matching letters.
               return isPalindrome(text, start + 1, end - 1);
            }
            else
            {
               return false;
            }
         }
         else if (!Character.isLetter(last))
         {
            // Test substring that doesn’t contain the last character.
            return isPalindrome(text, start, end - 1);
         }
         else
         {
            // Test substring that doesn’t contain the first character.
            return isPalindrome(text, start + 1, end);
         }
      }
   }   
}

