Java program to check Palindrome

A palindrome is a word, phrase, number, or other sequence of symbols or elements that reads the same forward or reversed.

For example: 12121 is palindrome as it reads same forward or reversed. madam is also a palindrome .
This is very simple interview question.There are many ways to check if given string is palindrome or not.

Reversing a String and then comparing it with input String:

package org.arpit.java2blog;

import java.util.Scanner;

public class StringFullLoopPalindrome {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.print("Enter string : ");

String str = scanner.nextLine();

String reverseStr = "";

for(int i = str.length() - 1; i >= 0; i--){

reverseStr = reverseStr + str.charAt(i);

}

if(str.equals(reverseStr)){

System.out.println("String is palindrome");

} else {

System.out.println("String is not palindrome");

}

Run above program, you will get following output:

Enter string : 12121

String is palindrome

Enter a string : Apple

String is not palindrome

Using half loop,Moving from both end of String simultaneously:

package org.arpit.java2blog;

import java.util.Scanner;

public class StringUsingHalfLoop {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.print("Enter a string : ");

String str = scanner.nextLine();

boolean isPalin=isPalindrome(str);

if(isPalin)

System.out.println("String is Palindrome");

else

System.out.println("String is not Palindrome");

}

static boolean isPalindrome(String str)

{

for (int i = 0,j=str.length()-1; i <str.length()/2; i++,j--) {

if(str.charAt(i)!=str.charAt(j))

{

return false;

}

return true;

}

Run above program, you will get following output:

Enter a string : madam

String is Palindrome

Enter a string : adam

String is not Palindrome

Using StringBuilder’s reverse() function:

package org.arpit.java2blog;

import java.util.Scanner;

public class StringPalindrome {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.print("Enter string : ");

String str = scanner.nextLine();

StringBuilder strBuilder = new StringBuilder(str);

strBuilder.reverse();

if(str.equals(strBuilder.toString())){

System.out.println("String is palindrome");

} else {

System.out.println("String is not palindrome");

}

Run above program, you will get following output:

Enter a string : stats

String is palindrome

Enter a string : 1212121

String is palindrome

Please go through java interview programs for more such programs.

You can also check Python program to check if String is palindrome.

Java2Blog

Java program to check Palindrome

Reversing a String and then comparing it with input String:

Using half loop,Moving from both end of String simultaneously:

Using StringBuilder’s reverse() function:

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Reversing a String and then comparing it with input String:

Using half loop,Moving from both end of String simultaneously:

Using StringBuilder’s reverse() function:

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