Java Interview Question: Check if a String is a Palindrome

 🔹 Introduction

String problems are very common in Java interviews.
One of the easiest yet frequently asked questions is:

👉 Check whether a given string is a palindrome.

Let’s understand how to solve it step by step.

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🔹 Problem Statement

A string is called a palindrome if it reads the same forward and backward.

Example:

Input: madam  
Output: Palindrome  

Input: hello  
Output: Not a Palindrome  

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🔹 Approach 1: Using Two Pointers (Best Method)

1. Start one pointer from the beginning
2. Start another pointer from the end
3. Compare characters
4. If all match → Palindrome

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🔹 Java Code (Two Pointer Approach)

public class PalindromeCheck {
    public static void main(String[] args) {
        String str = "madam";

        int left = 0;
        int right = str.length() - 1;
        boolean isPalindrome = true;

        while (left < right) {
            if (str.charAt(left) != str.charAt(right)) {
                isPalindrome = false;
                break;
            }
            left++;
            right--;
        }

        if (isPalindrome) {
            System.out.println("Palindrome");
        } else {
            System.out.println("Not a Palindrome");
        }
    }
}

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🔹 Approach 2: Using StringBuilder (Simple Method)

Reverse the string and compare.

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🔹 Java Code (StringBuilder)

public class PalindromeCheck {
    public static void main(String[] args) {
        String str = "madam";

        String reversed = new StringBuilder(str).reverse().toString();

        if (str.equals(reversed)) {
            System.out.println("Palindrome");
        } else {
            System.out.println("Not a Palindrome");
        }
    }
}

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🔹 Time Complexity

• O(n) → Efficient solution

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🔹 Key Takeaways

✔ Two-pointer approach is optimal
✔ StringBuilder makes it simple
✔ Very frequently asked in interviews

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🔹 Conclusion

Palindrome is one of the most basic and important string problems.
Make sure you understand both approaches for interviews.

🔗 Also Read

👉 First Non-Repeating Character in Java
👉 Check Palindrome String in Java