Java Program to Check Palindrome

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Program to Check Palindrome

In this article, we will learn multiple ways to check whether a number is palindrome or not in Java.

Palindrome Number:

A number is said to be a palindrome number if reverse of a number is same as that of the original number.

E.g. 131, 9865689, 1234321, 555 are palindrome numbers

And our task is to find out different approaches to check whether a number is Palindrome or not. We will see to implement this.

Let’s see different approaches one by one.

Check a number is Palindrome or not using While Loop
Check a number is Palindrome or not using For Loop
Check a number is Palindrome or not by taking user input
Check a number is palindrome or not using Static method
Check a number is Palindrome or not using Recursion

Method-I:- Check a number is Palindrome or not using While Loop

Using a while loop a number can be checked if it is palindrome or not. Initially we store the number in a variable say orgno. Then by taking a while loop we will calculate reverse of a number. Then we will check if that variable orgno is equal to the number calculated in while loop. If condition satisfied, print the number is palindrome. Otherwise, the number is not palindrome.

Approach:

Declare and initialize int variable no (number to checked) and revno to 0.
Declare int variable rem to contain remainder.
Initially store no in a variable say orgno
Take a while loop and iterate until no!=0
Inside while loop implement the following
Store no%10 in rem
Implement revno * 10 + rem and store in revno
Make no/10 and store in no
After the while loop condition fails, revno will contain reverse of no
Taking if condition check if orgno=revno, if yes it is palindrome.
Otherwise, it is not palindrome.

Program:

class CheckPalindome 
{
  public static void main(String[] args) 
{
    
    int no = 12421, revno = 0, rem;
    
    // store the number in orgnum
    int orgno = no;
    
    // get the reverse of no and store in revno
    while (no != 0) {
      rem = no % 10;
      revno = revno * 10 + rem;
      no /= 10;
    }
    
    // check if revno and orgno i.e. no are equal
    if (orgno == revno) {
      System.out.println(orgno + " is a Palindrome number.");
    }
    else {
      System.out.println(orgno + " is not a Palindrome number.");
    }
  }
}

Output:

12421 is a Palindrome number.

Method-II:- Check a number is Palindrome or not using For Loop

We can check a number is palindrome or not using a for loop. Initially we store the number in an integer variable say orgno. Then by taking a for loop we will calculate reverse of a number. Then we will check if that variable orgno is equal to the number calculated in for loop. If condition satisfied, print the number is palindrome. Otherwise, the number is not palindrome.

Approach:

Declare and initialize int variable no (number to checked) and revno to 0.
Declare int variable rem which will contain remainder.
Initially store no in a variable say orgno
Take a for loop iterate till no!=0 then make no/10
Store no%10 in rem
Implement revno * 10 + rem and store in revno
After the for loop condition fails revno will contain reverse of no
Taking if condition check if orgno=revno, if yes it is palindrome.
Otherwise, it is not palindrome.

Program:

public class CheckPalindrome 
{
  
    public static void main(String[] args) 
    {
  
        int no=423321, revno=0, rem, orgno;
        // store the value of no in orgno
        orgno = no;
        // on each iteration no will be divided by 10
        for( ;no != 0; no /= 10 )
        {
            // store the remainder no/10 in rem
            rem = no % 10;
            // reversed number will be stored in revno
            revno= revno* 10 + rem;
        }
  
        // check if original no is equal to reverse no
        if (orgno== revno)
            System.out.println(orgno + " is a palindrome number.");
        else
            System.out.println(orgno + " is not a palindrome number.");
    }
}

Output:

423321 is not a palindrome number.

Method-III:- Check a number is Palindrome or not by taking user input

This method is almost similar to Method-I. But we only have to take the number as user input. Then proceed similarly as approach of Method-I.

Approach:

Declare and initialize int variable revno to 0.
Declare int variable no which will store number to be checked.
Take a number input from user.
Declare int variable rem to contain remainder.
Initially store no in a variable say orgno
Take a while loop and iterate until no!=0
Inside while loop implement the following
Store no%10 in rem
Implement revno * 10 + rem and store in revno
Make no/10 and store in no
After the while loop condition fails, revno will contain reverse of no
Taking if condition check if orgno=revno, if yes it is palindrome.
Otherwise, it is not palindrome.

Program:

import java.util.Scanner;
class Main 
{
  public static void main(String[] args) 
  {
    
    int no, revno = 0, rem;
    Scanner sc= new Scanner(System.in);
    System.out.println("Enter a number :  ");
    no= sc.nextInt();
    
    // store the number in 'orgno'
    int orgno = no;
    
    // get the reverse of 'no' and store in 'revno'
    while (no != 0) {
      rem = no % 10;
      revno = revno * 10 + rem;
      no /= 10;
    }
    
    // check if 'revno' and 'orgno' i.e. 'no' are equal
    if (orgno == revno) 
    {
      System.out.println(orgno + " is a Palindrome number.");
    }
    else 
    {
      System.out.println(orgno + " is not a Palindrome number.");
    }
  }
}

Output:

CASE-1
Enter a number :  131
131 is a Palindrome number.

CASE-2
Enter a number :  654
654 is not a Palindrome number.

Method-IV :- Check a number is palindrome or not using Static method

Static method is that method which belongs to class but not to the object. It will exist whatever may be the instance created for the class.

Approach:

Declare integer variable say revno, orgno.
Declare and initialize the number to be checked say int variable no.
Store the value of no in orgno.
Take a static method and pass no’s value in it.
In static method implement the following
Declare integer variable sum , num and initialize sum to 0.
Iterate while loop until passed value say n (given number) !=0.
Inside while implement the following.
Store n%10 in integer variable rem
And store (sum*10)+rem in sum.
Then do n=n/10.
After while loop executed come out of the loop and store the sum value to the calling method in main function.
Check whether returned value =orgno, print number is palindrome, otherwise not palindrome.

public class Main
{
    public static void main(String arg[])	
    {
        int revno;
        int no=12521;
        int orgno=no;
        // reverse no will be stored in revno
        revno=palindromeOrNot(no);
        // checks reverse number=original number
        if(revno==orgno)
        System.out.println(revno+" is a palindrome number ");
                   else
        System.out.println(revno+" is not a palindrome number ");                  
    }
    // static method to compute reverse no and return to main method
    static int  palindromeOrNot(int n)
    {
        int sum=0,rem;
        // get reverse of number
        while(n!=0)
        {
        rem=n%10;
        sum=(sum*10)+rem;
        n/=10;	
        }
    // return reverse number to calling method
    return sum;
    }
}

Output:

12521 is a palindrome number

Method-V :- Check a number is Palindrome or not using Recursion

Here a static method will be as recursive function. It will execute recursively and return the reversed number. If it is equal to the original number then the number is palindrome, otherwise not.

Approach

Declare and initialize integer variable say no which is the number to be checked.
Initialize integer variable say revno
Take static method say revRecursion
Create static method which will accept arguments passed in main function i.e. static int revRecursion(int no, int revno)
Since the method will execute recursively, so execute it until no becomes 0.
Implement (revno * 10) + (no % 10) and store in revno. After some executions return no/10 and revno.
In main function the returned value will be stored in revno.
Check if revno=no, it is a palindrome number.
otherwise it is not a palindrome.

Program:

public class CheckPalindrome
{
 
// recursive method will execute until no becomes 0
static int revRecursion(int no, int revno)
{
    // if no becomes 0 return revno
    if (no == 0)
        return revno;
 
    // reverse of no stored in revno
    revno = (revno * 10) + (no % 10);
    
    
    // no will be divided by 10 
    // will again call recursive method
    return revRecursion(no / 10, revno);
}
 
// Driver Code
public static void main (String[] args)
{
    int no = 9658569;
    // store the returned value from recursion method in revno
    int revno = revRecursion(no, 0);
    // check if reversed number = original number
    if (revno == no)
        System.out.println(no+" is a Palindrome number.");
    else
        System.out.println(no+" is a Palindrome number" );
}
}

Output:

9658569 is a Palindrome number.

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