Palindrome in Java: How to check a number is palindrome?

When people interview for Java, they are normally tested for their logic and programming skills. One of the most frequently asked questions is Palindrome program in Java. Palindrome is nothing but any number or a string which remains unaltered when reversed. For example: 12321 or MAAM. It is evident that letters form mirror images on reversal.

Palindrome Program using While Loop

This is one of the easiest programs to find Palindrome program using ‘For Loop’. Let’ dive into an example to check whether a given input is a palindrome or not.

public class PalindromeProgram {

    public static void main(String[] args) {

        int rem, rev= 0, temp;
	int n=121; // user defined number to be checked for palindrome 

        temp = n;

        // reversed integer is stored in variable 
        while( n != 0 )
        {
            rem= n % 10;
            rev= rev * 10 + rem;
            n=n/10;
        }

        // palindrome if orignalInteger(temp) and reversedInteger(rev) are equal
        if (temp == rev)
            System.out.println(temp + " is a palindrome.");
        else
            System.out.println(temp + " is not a palindrome.");
    }
}

Output: 121 is a palindrome number

Explanation: Input the number you want to check and store it in a temporary(temp) variable. Now reverse the number and compare whether the temp number is same as the reversed number or not. If both the numbers are same, it will print palindrome number, else not a palindrome number.

Note: The logic of the Palindrome program remains the same, but the execution differs.

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Now that you are clear with the logic, let’s try to implement the palindrome program in Java in another way i.e using while loop.

Palindrome program using For Loop

public class PalindromeProgram {
 
    public static void main(String[] args) {
 
        int n=1234521, rev=0, rem, temp;
 
        temp = n;
 
        for( ;n != 0; n /= 10 )
        {
            rem = n % 10;
            rev= rev* 10 + rem;
        }
 
        // palindrome if temp and sum are equal
        if temp== rev)
            System.out.println(temp + " is a palindrome.");
        else
            System.out.println(temp + " is not a palindrome.");
    }
}

Output: 1234521 is not a palindrome

Palindrome Program in Java (String) using Library Method

In this section, we will find palindrome of a Java string. It works in the same way as that of integers, For example, “madam” is a palindrome, but “madame” is not a palindrome. Let’s implement this palindrome program in Java using string reverse function.

class PalindromeProgram
{
public static void checkPalindrome(String s)
{
// reverse the given String
String reverse = new StringBuffer(s).reverse().toString();

// checks whether the string is palindrome or not
if (s.equals(reverse))
System.out.println("Yes, it is a palindrome");

else
System.out.println("No, it is not a palindrome");
}

public static void main (String[] args)
throws java.lang.Exception
{
checkPalindrome("madam");
}
}

Output: Yes, it is a palindrome