Write a Java program that checks whether a string is a palindrome or not.

The provided Java program checks whether a string is a palindrome or not. A palindrome is a word or phrase that reads the same forward and backward (ignoring spaces, punctuation, and case).

class Main {
    public static void main(String[] args) {
        String str = "madam";
        if (isPalindromeString(str)) {
            System.out.print("is palindrome string.");
        } else {
            System.out.print("is not palindrome string");
        }
    }

    public static boolean isPalindromeString(String str) {
        str = str.toLowerCase(); // Convert string to lowercase for case-insensitive comparison
        int start = 0;
        int end = str.length() - 1;
        while (start < end) {
            if (str.charAt(start) != str.charAt(end)) {
                return false; // If characters don't match, return false
            }
            start++;
            end--;
        }
        return true; // If all character pairs match, return true
    }
}

Output:

is palindrome string.

The provided Java program checks whether a string is a palindrome or not. A palindrome is a word or phrase that reads the same forward and backward (ignoring spaces, punctuation, and case). Here’s a breakdown of the code:

How It Works

1. Input String:
   • The input string is “madam”.
2. isPalindromeString Method:
   • The method converts the string to lowercase to ensure the comparison is case-insensitive (i.e., ‘M’ and ‘m’ are treated as the same).
   • It uses two pointers: one starting at the beginning of the string (start) and the other at the end (end).
   • The method compares the characters at start and end. If they are not equal, it returns false (i.e., the string is not a palindrome).
   • If all corresponding characters match, it returns true (i.e., the string is a palindrome).

Execution:

1. Convert string to lowercase: “madam”
2. Compare characters from both ends:
   • ‘m’ == ‘m’ (start = 0, end = 4)
   • ‘a’ == ‘a’ (start = 1, end = 3)
   • ‘d’ == ‘d’ (start = 2, end = 2)
3. All characters match, so the method returns true.

Edge Cases

1. Empty String:
   • Input: “”
   • Output: is palindrome string. (An empty string is considered a palindrome).
2. Single Character String:
   • Input: “A”
   • Output: is palindrome string. (A single character is always a palindrome).
3. String with Different Case:
   • Input: “MadAm”
   • Output: is palindrome string. (Case is ignored because the string is converted to lowercase).
4. Non-Palindrome String:
   • Input: “hello”
   • Output: is not palindrome string. (The characters do not match from both ends).

Advantages

• Efficient: The solution compares characters from both ends and moves towards the center, reducing the number of comparisons needed.
• Case-Insensitive: The program handles case differences (i.e., ‘M’ and ‘m’ are treated equally).