Palindromes.java.html

  1  public class Palindromes
  2  {
  3     public static void main(String[] args)
  4     {
  5        String sentence1 = "Madam, I'm Adam!";      
  6        System.out.println(sentence1);
  7        System.out.println("Palindrome: " + isPalindrome(sentence1));
  8        String sentence2 = "Sir, I'm Eve!";      
  9        System.out.println(sentence2);
 10        System.out.println("Palindrome: " + isPalindrome(sentence2));
 11     }
 12  
 13     /**
 14        Tests whether a text is a palindrome.
 15        @param text a string that is being checked
 16        @return true if text is a palindrome, false otherwise
 17     */
 18     public static boolean isPalindrome(String text)
 19     {
 20        return isPalindrome(text, 0, text.length() - 1);      
 21     }
 22  
 23     /**
 24        Tests whether a substring is a palindrome.
 25        @param text a string that is being checked
 26        @param start the index of the first character of the substring
 27        @param end the index of the last character of the substring
 28        @return true if the substring is a palindrome
 29     */
 30     public static boolean isPalindrome(String text, int start, int end)
 31     {
 32        // Separate case for substrings of length 0 and 1.
 33        if (start >= end) { return true; }
 34        else
 35        {
 36           // Get first and last characters, converted to lowercase.
 37           char first = Character.toLowerCase(text.charAt(start));
 38           char last = Character.toLowerCase(text.charAt(end));
 39           if (Character.isLetter(first) && Character.isLetter(last))
 40           {
 41              if (first == last)
 42              {
 43                 // Test substring that doesn’t contain the matching letters.
 44                 return isPalindrome(text, start + 1, end - 1);
 45              }
 46              else
 47              {
 48                 return false;
 49              }
 50           }
 51           else if (!Character.isLetter(last))
 52           {
 53              // Test substring that doesn’t contain the last character.
 54              return isPalindrome(text, start, end - 1);
 55           }
 56           else
 57           {
 58              // Test substring that doesn’t contain the first character.
 59              return isPalindrome(text, start + 1, end);
 60           }
 61        }
 62     }   
 63  }