In this post we will learn how to check whether a given String/Number is a Palindrome or not in java.
Before start writing a java program let’s try to understand.
What is Palindrome?
If a String or a Number is a palindrome if it remains unchanged when reversed, for example “mom” is a palindrome as reverse of the mom is again mom. Another example is “malayalam” or 12344321.
You may refer Reverse a string in Java program with 5 Different Ways that may be helpful to you to understand the logic used behind the Palindrome check program
Approach 1:
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package com.kkjavatutorials.client; import java.util.Scanner; /** * @author KK JavaTutorials Java program to Check Whether a Given String/Number * is a Palindrome or not */ public class ClientTest1 { public static void main(String[] args) { try (Scanner scanner = new Scanner(System.in)) { // Taking input from keyboard using Scanner System.out.println("Enter string which you want to check whether Palindrome or not::"); String inputText = scanner.next(); checkInputTextPalindrome(inputText); } catch (Exception e) { System.out.println(e.getMessage()); } } private static void checkInputTextPalindrome(String inputText) { // base case if input is null or empty if (inputText == null || inputText.trim().isEmpty()){ System.out.println("Enter valid input text.."); return; } boolean isPalidrome =false; String reversedOutput = reverseInput(inputText); if(inputText.equalsIgnoreCase(reversedOutput)) isPalidrome = true; if(isPalidrome) System.out.println("Input String is Palidrome."); else System.out.println("Input String is not palidrome."); } private static String reverseInput(String inputText) { String reverse = ""; for (int i = inputText.length()-1; i>=0 ; i--) { char c = inputText.charAt(i); reverse = reverse+c; } return reverse; } } |
Approach 2:
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package com.kkjavatutorials.client; import java.util.Scanner; /** * @author KK JavaTutorials Java program to Check Whether a Given String/Number * is a Palindrome or not */ public class ClientTest2 { public static void main(String[] args) { try (Scanner scanner = new Scanner(System.in)) { // Taking input from keyboard using Scanner System.out.println("Enter string which you want to check whether Palindrome or not::"); String inputText = scanner.next(); checkInputTextPalindrome(inputText); } catch (Exception e) { System.out.println(e.getMessage()); } } private static void checkInputTextPalindrome(String inputText) { // base case if input is null or empty if (inputText == null || inputText.trim().isEmpty()){ System.out.println("Enter valid input text.."); return; } boolean isPalidrome =false; String reversedOutput = reverseInput(inputText); if(inputText.equalsIgnoreCase(reversedOutput)) isPalidrome = true; if(isPalidrome) System.out.println("Input String is Palidrome."); else System.out.println("Input String is not palidrome."); } private static String reverseInput(String inputText) { String reverse = ""; //Convert string into character array char[] charArray = inputText.toCharArray(); for (int i = inputText.length()-1; i>=0 ; i--) { reverse +=charArray[i]; } return reverse; } } |
Approach 3:
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package com.kkjavatutorials.client; import java.util.Scanner; /** * @author KK JavaTutorials Java program to Check Whether a Given String/Number * is a Palindrome or not */ public class ClientTest3 { public static void main(String[] args) { try (Scanner scanner = new Scanner(System.in)) { // Taking input from keyboard using Scanner System.out .println("Enter string which you want to check whether Palindrome or not::"); String inputText = scanner.next(); checkInputTextPalindrome(inputText); } catch (Exception e) { System.out.println(e.getMessage()); } } private static void checkInputTextPalindrome(String inputText) { // base case if input is null or empty if (inputText == null || inputText.trim().isEmpty()) { System.out.println("Enter valid input text.."); return; } boolean isPalidrome = false; String reversedOutput = reverseInput(inputText); if (inputText.equalsIgnoreCase(reversedOutput)) isPalidrome = true; if (isPalidrome) System.out.println("Input String is Palidrome."); else System.out.println("Input String is not palidrome."); } private static String reverseInput(String inputText) { // Convert string into byte array byte[] bytes = inputText.getBytes(); byte[] revByteArr = new byte[bytes.length]; for (int i = 0; i < bytes.length; i++) { revByteArr[i] = bytes[bytes.length - i - 1]; } String reverseString = new String(revByteArr); return reverseString; } } |
Approach 4:
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package com.kkjavatutorials.client; import java.util.Scanner; /** * @author KK JavaTutorials Java program to Check Whether a Given String/Number * is a Palindrome or not */ public class ClientTest4 { public static void main(String[] args) { try (Scanner scanner = new Scanner(System.in)) { // Taking input from keyboard using Scanner System.out .println("Enter string which you want to check whether Palindrome or not::"); String inputText = scanner.next(); checkInputTextPalindrome(inputText); } catch (Exception e) { System.out.println(e.getMessage()); } } private static void checkInputTextPalindrome(String inputText) { // base case if input is null or empty if (inputText == null || inputText.trim().isEmpty()) { System.out.println("Enter valid input text.."); return; } boolean isPalidrome = false; String reversedOutput = reverseInput(inputText); if (inputText.equalsIgnoreCase(reversedOutput)) isPalidrome = true; if (isPalidrome) System.out.println("Input String is Palidrome."); else System.out.println("Input String is not palidrome."); } private static String reverseInput(String inputText) { // Convert string into character array char[] inputByteArray = inputText.toCharArray(); int left, right = inputByteArray.length - 1; for (left = 0; left < right; left++, right--) { // Swap values of left and right index char temp = inputByteArray[left]; inputByteArray[left] = inputByteArray[right]; inputByteArray[right] = temp; } String reverseString = new String(inputByteArray); return reverseString.toString(); } } |
Approach 5:
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package com.kkjavatutorials.client; import java.util.Scanner; /** * @author KK JavaTutorials Java program to Check Whether a Given String/Number * is a Palindrome or not */ public class ClientTest1 { public static void main(String[] args) { try (Scanner scanner = new Scanner(System.in)) { // Taking input from keyboard using Scanner System.out.println("Enter string which you want to check whether Palindrome or not::"); String inputText = scanner.next(); checkInputTextPalindrome(inputText); } catch (Exception e) { System.out.println(e.getMessage()); } } private static void checkInputTextPalindrome(String inputText) { boolean isPalidrome =false; // base case if input is null or empty if (inputText == null || inputText.trim().isEmpty()){ System.out.println("Enter valid input text.."); return; } /* * Here I have used StringBuilder class if you required thread safety then * you may use StringBuffer class which has also reverse method */ StringBuilder sb = new StringBuilder(inputText); sb.reverse(); String reversedOutput = sb.toString(); //Above action may be perform in single line,Just to make you understand i have splitted into three lines. //String reversedOutput = new StringBuilder(inputText).reverse().toString(); if(inputText.equalsIgnoreCase(reversedOutput)) isPalidrome = true; if(isPalidrome) System.out.println("Input String is Palidrome."); else System.out.println("Input String is not palidrome."); } } |
I have checked all the above programs for few inputs as below. You may check for other input as well
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Enter string which you want to check whether Palindrome or not:: malayalam Input String is Palidrome. Enter string which you want to check whether Palindrome or not:: 12344321 Input String is Palidrome. Enter string which you want to check whether Palindrome or not:: KKJavaTutorials Input String is not palidrome. |
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