Java Program to Check Palindrome String or not

Java Program to Check Palindrome String or not using for loop

A string is a palindrome if it remains unchanged when reversed the string.

Example 'madam': reversed string is also madam, so this string is a palindrome.

String 'testing' : reversed string is 'gnitset', so this string is not a palindrome.

This java program accepts the string entered by user, reverses the string and compares the reversed string with original string to check palindrome or not.

length method is used to get the number of characters in the string.

charAt method is used to get the character of the specified index in the string.

import java.util.*; 

public class PalindromeString
{ 
   public static void main(String args[]) { 
 	Scanner sc=new Scanner(System.in);
 	System.out.println("Check Palindrome String or not"); 
 	System.out.println("------------------------------"); 
 	System.out.print("Enter String: "); 
 	String str = sc.nextLine();
 	String reverse = "";

 	for(int i=str.length()-1;i>=0;i--){
 		reverse = reverse + str.charAt(i);
 	}
 	if (str.equals(reverse)){
 		System.out.println("String '"+str+"' is a Palindrome!");
 	} else {
 		System.out.println("String '"+str+"' is not a Palindrome!");
 	}

   } 
}  

D:\Java_Programs>javac PalindromeString.java
D:\Java_Programs>java PalindromeString
Check Palindrome String or not
------------------------------
Enter String: aabaa
String 'aabaa' is a Palindrome!

D:\Java_Programs>javac PalindromeString.java
D:\Java_Programs>java PalindromeString
Check Palindrome String or not
------------------------------
Enter String: testing
String 'testing' is not a Palindrome!

Java Program to Check Palindrome String or not using while loop

import java.util.*; 

public class PalindromeString
{ 
   public static void main(String args[]) { 
 	Scanner sc=new Scanner(System.in);
 	System.out.println("Check Palindrome String or not"); 
 	System.out.println("------------------------------"); 
 	System.out.print("Enter String: "); 
 	String str = sc.nextLine();
 	String reverse = "";
 	int i=str.length()-1;
 	while(i>=0){
 		reverse = reverse + str.charAt(i);
 		i--;
 	}
 	if (str.equals(reverse)){
 		System.out.println("String '"+str+"' is a Palindrome!");
 	} else {
 		System.out.println("String '"+str+"' is not a Palindrome!");
 	}
   } 
} 

D:\Java_Programs>javac PalindromeString.java
D:\Java_Programs>java PalindromeString
Check Palindrome String or not
------------------------------
Enter String: dad
String 'dad' is a Palindrome!

Java Program to Check Palindrome String or not using recursion

import java.util.*; 

public class PalindromeString
{ 
	public static String reverse(String original, String rev, int index){
		if(index>=0) {
			return original.charAt(index)+reverse(original, rev, index-1);
		}
		return "";
	}
   public static void main(String args[]) { 
 	Scanner sc=new Scanner(System.in);
 	System.out.println("Check Palindrome String or not"); 
 	System.out.println("------------------------------"); 
 	System.out.print("Enter String: "); 
 	String str = sc.nextLine();
 	String rev = "";
 	int i=str.length()-1;
 	rev = reverse(str, rev, i);
 	if (str.equals(rev)){
 		System.out.println("String '"+str+"' is a Palindrome!");
 	} else {
 		System.out.println("String '"+str+"' is not a Palindrome!");
 	}

   } 
} 

D:\Java_Programs>javac PalindromeString.java
D:\Java_Programs>java PalindromeString
Check Palindrome String or not
------------------------------
Enter String: madam
String 'madam' is a Palindrome!