Skip to content
Related Articles

Related Articles

Improve Article
Save Article
Like Article

Java program to check whether a string is a Palindrome

  • Difficulty Level : Basic
  • Last Updated : 23 Feb, 2022

A string is said to be a palindrome if it is the same if we start reading it from left to right or right to left. So let us consider a string “str”, now the task is just to find out with its reverse string is the same as it is. 

Illustration:

Input : str = "abba" 
Output: Yes
Input : str = "geeks"
Output: No  

In the above illustration, if we write ABba in place of abba, then also we should get the output as yes.  So, it is important that we change the case of the string to either lowercase or uppercase before we check it for a palindrome. If we do not do this, we will get unexpected results. This is because the compiler checks the characters based on their ASCII value and the ASCII value of A is not the same as a

Approach: Our approach will be that we will first convert the string to lowercase. Then, we will take two pointers i pointing to the start of the string and j pointing to the end of the string. Keep incrementing i and decrementing j while i < j and at every step check whether the characters at these pointers are same or not. If not then the string is not a palindrome else it is.

Example 1:

Java




// Java program to check whether a
// string is a Palindrome
// Using two pointing variables
 
// Main class
public class GFG {
 
    // Method
    // Returning true if string is palindrome
    static boolean isPalindrome(String str)
    {
 
        // Pointers pointing to the beginning
        // and the end of the string
        int i = 0, j = str.length() - 1;
 
        // While there are characters to compare
        while (i < j) {
 
            // If there is a mismatch
            if (str.charAt(i) != str.charAt(j))
                return false;
 
            // Increment first pointer and
            // decrement the other
            i++;
            j--;
        }
 
        // Given string is a palindrome
        return true;
    }
 
    // Method 2
    // main driver method
    public static void main(String[] args)
    {
        // Input string
        String str = "geeks";
 
        //Convert the string to lowercase
        str = str.toLowerCase();
        // passing bool function till holding true
        if (isPalindrome(str))
 
            // It is a palindrome
            System.out.print("Yes");
        else
 
            // Not a palindrome
            System.out.print("No");
    }
}


Output: 

No

 

Example 2:

Java




// Java Program to check Whether the String is Palindrome
// or Not
 
// Main class
class GFG {
 
    // Method 1
    // Returns true if string is a palindrome
    static boolean isPalindrome(String str)
    {
 
        // Pointers pointing to the beginning
        // and the end of the string
        int i = 0, j = str.length() - 1;
 
        // While there are characters to compare
        while (i < j) {
 
            // If there is a mismatch
            if (str.charAt(i) != str.charAt(j))
                return false;
 
            // Increment first pointer and
            // decrement the other
            i++;
            j--;
        }
 
        // Given string is a palindrome
        return true;
    }
 
    // Main driver method
    public static void main(String[] args)
    {
        String str = "geeks";
        String str2 = "RACEcar";
       
        //Change strings to lowercase
        str = str.toLowerCase();
        str2 = str2.toLowerCase();
 
        // For string 1
        System.out.print("String 1 :");
 
        if (isPalindrome(str))
            System.out.print("It is a palindrome");
        else
            System.out.print("It is not a palindrome");
 
        // new line for better readability
        System.out.println();
 
        // For string 2
        System.out.print("String 2 :");
        if (isPalindrome(str2))
            System.out.print("It is a palindrome");
        else
            System.out.print("It is not a palindrome");
    }
}


Output

String 1 :It is not a palindrome
String 2 :It is a palindrome

My Personal Notes arrow_drop_up
Recommended Articles
Page :

Start Your Coding Journey Now!