Chapter 16. PC #5. Palindrome Detector (page 1073) A palindrome is any word, phr

Question

Chapter 16. PC #5. Palindrome Detector (page 1073)
A palindrome is any word, phrase, or sentence that reads the same forward and 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 (JAVA) boolean method that uses recursion to determine whether 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.

The program should ask the user to enter a string, which is checked for palindrome property. The program displays whether the given input is a palindrome or not, then prompts the user to enter another string. If the user enters QUIT (case insensitive, then exit the program).

View required output

Test Case 1

  dadENTER  quitENTER  

Explanation / Answer

Below is your program: -

Palindrome.java

import java.util.Scanner;

class Palindrome {
   public static boolean isPal(String s) {

       // if length is 0 or 1 then String is palindrome
       if (s.length() == 0 || s.length() == 1)
           return true;
       // else check for each character.
       if (s.charAt(0) == s.charAt(s.length() - 1))

           return isPal(s.substring(1, s.length() - 1));

       return false;
   }

   public static void main(String[] args) {
       // For capturing user input
       Scanner scanner = new Scanner(System.in);
       String string = "";

       while (!string.equalsIgnoreCase("Quit")) {
           System.out.print("Please enter a string to test for palindrome or type QUIT to exit: ");
           string = scanner.nextLine();
           if (!string.equalsIgnoreCase("Quit")) {
               if (isPal(string))
                   System.out.println("The input is a palindrome.");
               else
                   System.out.println("The input is not a palindrome.");
           }
       }

   }
}

Sample Run:-

Please enter a string to test for palindrome or type QUIT to exit:
dad
The input is a palindrome.
Please enter a string to test for palindrome or type QUIT to exit:
sas
The input is a palindrome.
Please enter a string to test for palindrome or type QUIT to exit:
sss
The input is a palindrome.
Please enter a string to test for palindrome or type QUIT to exit:
sda
The input is not a palindrome.
Please enter a string to test for palindrome or type QUIT to exit:
123
The input is not a palindrome.
Please enter a string to test for palindrome or type QUIT to exit:
121
The input is a palindrome.
Please enter a string to test for palindrome or type QUIT to exit:
quit

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