Question

JAVA Palindrome Detector

A palindrome is any word, phrase, or sentence that reads the same forward or backward. Here are some well-known palindromes:

Able was I, ere I saw Elba

A man, a plan, a canal, Panama

Desserts, I stressed

Kayak

Write a boolean method that users recursion to determine where a String argument is a palindrome. The method should return true if the argument reads the same forward and backward. Demonstrate the method in a program.

Include the following modifications:

• Use JOptionPanes for all user I/O.
• Allow the user to input test strings until they type "quit" to exit.

Answer 1

import javax.swing.JOptionPane;

public class PalindromeRecursion {
   public static void main(String[] args) {
       String word = "";
       word = JOptionPane.showInputDialog("Enter word: ");

word=word.toUpperCase();

       while (!word.equalsIgnoreCase("quit")) {
           if (isPalindrome(word, 0, word.length() - 1)) {
               JOptionPane.showMessageDialog(null, word + " is Palindrome");
           } else {
               JOptionPane.showMessageDialog(null, word + " is not Palindrome");

           }
           word = JOptionPane.showInputDialog("Enter word: ");

       }
   }

   static boolean isPalindrome(String str, int start, int e) {
       if (start == e)
           return true;

       // checking first and last dont match
       // return false
       if ((str.charAt(start)) != (str.charAt(e)))
           return false;

       // if start is < end
       // than increase start and decrease end
       if (start < e + 1)
           return isPalindrome(str, start + 1, e - 1);

       return true;
   }

}