Palindrome: Java program to check number is palindrome or not

How to find if a number is a palindrome in Java
Checking whether a number is palindrome or not is a classical Java homework exercise. When you start learning Java programming most institute which teaches Java programming provides these classical Java programs like How to find Armstrong number in Java or how to find the Fibonacci number in Java using recursion etc. Write a Java program to check if the number is palindrome comes from the same category. For those who are not familiar with palindrome numbers, a palindrome number is a number which is equal to reverse of itself. For example, 121 is a palindrome because the reverse of 121 is 121, while 123 is not a palindrome in Java because the reverse of 123 is 321 and 121!=321. Finding a palindrome number is easy in Java, you just need to develop logic to reverse a number in Java.

Thankfully Java provides a couple of arithmetic operators like remainder(%) operator also known as modules operator, which returns remainder in division operator and division operator(/) which returns quotient. By using remainder and division operator in Java we can create program to check if the number is palindrome or not.

 

Java program – palindrome numbers in Java

Write a Java program to check if number is palindrome or notHere is a complete Java program to check if a given number is palindrome or not, This program works for both positive and negative numbers and displays if its palindrome irrespective of there sign. Any one-digit number including zero is always palindrome. This program is able to check two-digit, three-digit numbers for palindrome and effective go to any number in Java. Let’s see how to write a Java program to find palindrome numbers :





package testing;
import java.util.Scanner;
/**
 * Java program to check if the number is palindrome or not.
 * A number is called palindrome if the number and its reverse is equal
 * This Java program can also be used to reverse a number in Java
 */

public class NoClassDefFoundErrorDueToStaticInitFailure {

    public static void main(String args[]){
       
        System.out.println("Please Enter a number : ");
        int palindrome = new Scanner(System.in).nextInt();
       
        if(isPalindrome(palindrome)){
            System.out.println("Number : " + palindrome + " is a palindrome");
        }else{
            System.out.println("Number : " + palindrome + " is not a palindrome");
        }      
       
    }
 
    /*
     * Java method to check if a number is palindrome or not
     */

    public static boolean isPalindrome(int number) {
        int palindrome = number; // copied number into variable
        int reverse = 0;

        while (palindrome != 0) {
            int remainder = palindrome % 10;
            reverse = reverse * 10 + remainder;
            palindrome = palindrome / 10;
        }

        // if original and reverse of number is equal means
        // number is palindrome in Java
        if (number == reverse) {
            return true;
        }
        return false;
    }

}

Output:
Please Enter a number :
123
Number : 123 is not a palindrome
Please Enter a number :
121
Number : 123 is a palindrome


That’s all on how to check if a number is a palindrome or not in Java. If you are looking for answer to this question for interview purposes then better prepare a recursive version of the palindrome program in Java as well because of its common practice that programmer is expected to write java program using both recursion and iteration in Java. Let me know if you find any other way of checking palindrome in Java.

Further Learning
Data Structures and Algorithms: Deep Dive Using Java
Java Fundamentals: The Java Language
Complete Java Masterclass

Other Java homework programming exercise:

37 comments:

  1. Very good Program!
    Please correct the out put when it asks 121 is a palindrome....the result says
    123" is a palindrome... it should be 121 :)
    Cheers!

    ReplyDelete
  2. Hi, Thanks for this. The program is working well but I am trying to understand how the reverse(sort of where it came from) fits the program.

    ReplyDelete
  3. // Variations, using charAt

    public static boolean isPolindrome(int n) {

    String s = String.valueOf(n).toString();
    String rs = new StringBuffer(s).reverse().toString();

    for (int i=0; i<s.length(); i++) {
    if (s.charAt(i) != rs.charAt(i)) return false;
    }

    return true;
    }

    ReplyDelete
  4. Hi you dont even need to reverse the string .

    static boolean checkAlgoOne(int num) {

    boolean check = false;

    String number = Integer.toString(num);
    char[] chars = number.toCharArray();
    int len = chars.length;

    if (num < 0)
    check = false;
    if (num == 0 || num == 1)
    check = true;

    if (len % 2 != 1) {
    check = false;
    } else {

    for (int i = 0; i <= len / 2; i++) {
    if (chars[i] == chars[len - 1])
    check = true;
    }

    }
    return check;
    }

    cheers!

    ReplyDelete
    Replies
    1. 1221 is palindrome, but your program will say it's not

      Delete
    2. import java.util.Scanner;
      public class integerpolindrome {
      public static void main(String[] args) {
      int poly=0;
      System.out.println("enter the integr number :");//123
      int num= new Scanner(System.in).nextInt();
      int real=num;
      while(num!=0)
      {
      int rem=num%10;//3
      poly =rem+10*poly;
      num/=10;
      }
      if(poly==real)
      {
      System.out.println("its a polindrome number:");
      }
      else
      System.out.println("its not a polindrome number:");
      }

      }
      //try this one

      Delete
  5. My way:
    /* Palindrome Program In JAVA
    © Code Nirvana (www.codenirvana.in)
    */
    import java.util.Scanner;
    class Palindrome{
    public static void main(String args[]){
    System.out.print("Enter Number: ");
    Scanner read = new Scanner(System.in);
    int num = read.nextInt();
    int n = num;
    //reversing number
    int rev=0,rmd;
    while(num > 0)
    {
    rmd = num % 10;
    rev = rev * 10 + rmd;
    num = num / 10;
    }
    if(rev == n)
    System.out.println(n+" is a Palindrome Number!");
    else
    System.out.println(n+" is not a Palindrome Number!");
    }
    }

    MORE @ http://www.codenirvana.in/2013/10/Palindrome-Number-in-JAVA.html

    ReplyDelete
    Replies
    1. hi,

      can u explain why you have divided input by 10 and and %10 for reversing a number series...please explain that part.

      Delete
    2. Hello @Anonymous, when you divide the number you drop last digit from number and when you to module 10 i.. % 10 you get the last digit of the number.

      For example, 123/10 = 12, last digit 3 is gone so number reduced from 3 to 2
      123%10 = 3 means last digit.

      This is the trick you need to reverse the number.

      Delete
    3. why do we have 121/10=12 instead of 12.1

      Delete
    4. why do we have 121/10 as 12 instead of 12.1

      Delete
    5. You've probably figured this out by now but I will write the answer anyway in case someone else stumbles upon this thread.
      The answer is simple - because it's an integer, and integers are whole numbers. For the number to store 12.1 it would have to be a double or a float, both of which allow fractions.

      Delete
  6. private static boolean isPalindrome(int n) {
    return n == Integer.valueOf(new StringBuilder(String.valueOf(n)).reverse().toString());
    }

    ReplyDelete
  7. private void checkPolyndrom(String st) {
    boolean polyn=true;
    for(int i =0; i<st.length()-1/2; i++){
    if(st.charAt(i)==st.charAt(st.length()-1-i) && polyn){
    polyn=true;
    }else{
    polyn=false;
    }
    }
    if(polyn){
    System.out.println("Polyndrom");
    }else{
    System.out.println("Not Polyndrom");
    }

    }

    ReplyDelete
  8. Why do we multiply rev*10+ remainder

    ReplyDelete
  9. all are from which standards

    ReplyDelete
  10. Is 1221 a palindrome number. ????

    ReplyDelete
  11. public static boolean isPalindrome(int n) {
    String i = Integer.toString(n);
    int first = 0;
    int last = i.length() - 1;

    while (first < last) {
    if (i.charAt(first) == i.charAt(last)) {
    first++;
    last--;
    } else {
    return false;
    }
    }
    return true;
    }

    ReplyDelete
  12. good examples and thanks to all..

    ReplyDelete
  13. how to close the scanner int function?? for resolving warning.

    ReplyDelete
  14. try this simple way

    import java.util.*;
    class StringPalindrome
    {
    public static void main (String ar[])
    {
    String a, b;
    StringBuffer sb;
    Scanner sc=new Scanner (System.in);
    System.out.println("Ente rhe string");
    a=sc.nextLine();
    sb=new StringBuffer(a);
    b=sb.reverse().toString();
    if(a.equals(b))
    {
    System.out.println("The string is palidrome");
    }
    else
    {
    System.out.println("The string is not a palindrome");
    }}}

    ReplyDelete
  15. public static boolean isNumberPalindrome(int str) {

    return str == Integer.parseInt(new StringBuilder().append(str).reverse().toString());
    }

    ReplyDelete
  16. Palindrome Check using HashSet:
    import java.util.HashSet;
    import java.util.Set;

    public class p16 {


    public static void main(String[] args) {
    String a = "malayalam1";


    System.out.println(ispalindrome(a));

    }

    private static boolean ispalindrome(String a) {

    Set set = new HashSet<>();
    for (int i = 0; i < a.length(); i++) {
    char ch = a.charAt(i);
    if(set.contains(ch)) {
    set.remove(ch);
    }else {
    set.add(ch);
    }
    }
    return set.size() <= 1 ;

    }

    }

    ReplyDelete
  17. Integer i = 1221;
    char word[] = i.toString().toCharArray();

    int i1 = 0;
    int i2 = word.length - 1;
    while (i2 > i1) {
    if (word[i1] != word[i2]) {
    System.out.println("not palindrome");
    break;
    }
    ++i1;
    --i2;
    }

    ReplyDelete
  18. if(i==s.length()%2)
    {
    System.out.println("Palidrome");
    }

    ReplyDelete
  19. public class NumberPalindrome {
    public static boolean isPalindrome(int number)
    {
    int rem=0,reverse=0,start=number;
    while(number!=0)
    {
    rem=number%10;
    reverse=(reverse*10) +rem;
    System.out.println("rev= "+reverse);
    number=number/10;


    }

    if(reverse==start)
    return true;


    return false;

    }

    }

    ReplyDelete
  20. It is harder to understand with numbers than with string.

    ReplyDelete
    Replies
    1. Yeah, you need to know how to get the last digit of an number (remainder of divide by 10) and how to reduce 3 digit to 2 digit (divide by 10). If you don't know this trick then its a difficult problem to solve.

      Delete
  21. This program fails for numbers starting with a 0...Please correct your code..

    ReplyDelete
    Replies
    1. number starting with zero? that's not the valid number, how do you distinguish between 10 and 010? unless you are using string.

      Delete
  22. public class Palanadrone {
    public static void main(String[] args)
    {
    //////////// for integer
    int a=1551;
    if(String.valueOf(a).equals(new StringBuffer(String.valueOf(a)).reverse().toString()))
    System.out.println("the number is palandrone");
    else
    System.out.println("the number is not palandrone");
    /////////// for string
    String s4="teet";
    if(s4.equals(new StringBuilder(s4).reverse().toString()))
    System.out.println("the string is palandrone");
    else
    System.out.println("the string is not palandrone");
    }
    }

    ReplyDelete
    Replies
    1. That's cool but in interview you may not be allowed to use the reverse() method, Can you solve this problem without using StringBuffer or StringBuilder and reverse method?

      Delete
  23. package javaapplication6;

    import java.util.Scanner;

    /**
    *
    * @author MANISHA
    */
    public class JavaApplication6 {


    /**
    * Java program to check if the number is palindrome or not.
    * A number is called palindrome if the number and its reverse is equal
    * This Java program can also be used to reverse a number in Java
    */

    public static void main(String args[]){

    System.out.println("Please Enter a number : ");
    Scanner console = new Scanner(System.in);
    int palindrome=console.nextInt();

    if(isPalindrome(palindrome)){
    System.out.println("Number is a palindrome");
    }
    else
    {
    System.out.println("Number is not a palindrome");
    }

    }

    /*
    * Java method to check if a number is palindrome or not
    */
    public static boolean isPalindrome(int number) {
    int palindrome = number; // copied number into variable
    int reverse = 0;

    while (palindrome != 0) {
    int remainder = palindrome % 10;
    reverse = reverse * 10 + remainder;
    palindrome = palindrome / 10;
    }

    // if original and reverse of number is equal means
    // number is palindrome in Java
    if (number == reverse) {
    return true;
    }
    return false;
    }
    }

    ReplyDelete

Feel free to comment, ask questions if you have any doubt.