How to check if a number is palindrome in Java?

Question

I am new in Java and I need to complete this program to check if an integer is palindrome. Please help.

public static void main(String args[]){

    System.out.println("Please enter an integer : ");
    int integer = new Scanner(System.in).nextInt();

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

}

Possible duplicate of [Check string for palindrome](http://stackoverflow.com/questions/4138827/check-string-for-palindrome) — Alex Romanov, Apr 20 '17 at 09:52
This code has already been completed and a simple search would have found it. — Peter Lawrey, Apr 20 '17 at 10:01

Sky · Accepted Answer · 2017-04-20T10:25:20.217

13

public static boolean isPalindrome(int integer) {
    int palindrome = integer;
    int reverse = 0;

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

    // The integer is palindrome if integer and reverse are equal
    return integer == reverse; // Improved by Peter Lawrey

}

Advanced solution: (Provided by Shadov)

public static boolean isPalindrome(int integer) {
    String intStr = String.valueOf(integer); 
    return intStr.equals(new StringBuilder(intStr).reverse().toString());
}

Reference: http://www.java67.com/2012/09/palindrome-java-program-to-check-number.html#ixzz4emXfiD7V

Please do not just put up question without your work next time.

edited Apr 20 '17 at 10:25

answered Apr 20 '17 at 09:54

Sky

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avoid answering off topic questions.. also how is this any different from the other one? – Suraj Rao Apr 20 '17 at 09:56
2

why not `return integer == reverse;`? – Peter Lawrey Apr 20 '17 at 09:59
Nice catch, Peter. – Sky Apr 20 '17 at 10:01
@PeterLawrey because it's simply picked up from http://www.java67.com/2012/09/palindrome-java-program-to-check-number.html#ixzz4emXfiD7V :) – Hello Kitty Apr 20 '17 at 10:02
2

@SrishtiRanjan I agree, but just because you copied someone else's work doesn't mean you shouldn't try to improve it. ;) – Peter Lawrey Apr 20 '17 at 10:03
1

@PeterLawrey Yes, you are right. Nice one. :) – Sky Apr 20 '17 at 10:04
@PeterLawrey spot on! :D – Hello Kitty Apr 20 '17 at 10:07
2

Just for future generations: `String.valueOf(number).equals(new StringBuilder(String.valueOf(number)).reverse().toString());` – Shadov Apr 20 '17 at 10:14
@Shadov Thanks for the improvement. – Sky Apr 20 '17 at 10:20
@SkyLuke Oh, you added that to your answer, then you can extract `String.valueOf(number)` into variable so it's not called twice for the same argument :) – Shadov Apr 20 '17 at 10:22
@Shadov Ok, sure :) – Sky Apr 20 '17 at 10:24
how do you deal with the integer overflow issue without writing code to explicitly dealing with it? – munmunbb Aug 24 '17 at 06:26
The implementation only using int does not handle negative numbers. – user2524908 Mar 08 '18 at 01:26
if ( x < 0 ) { return false; } – Droid Teahouse Oct 05 '18 at 08:22
String operations takes about double the time of integer operations. – Amr Lotfy Dec 30 '18 at 16:11

score 1 · Answer 2 · answered Apr 20 '17 at 09:54

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;
}

Source: http://www.java67.com/2012/09/palindrome-java-program-to-check-number.html#ixzz4emXfiD7V

But you need to clearly not put up homework questions here.

How you guys (@sky and @Srishti) managed to answer on same time :D — dip, Feb 19 '18 at 05:05

How to check if a number is palindrome in Java?

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