Write a Java program that checks whether a given number is a prime number or not.

What is a Prime Number?

A prime number is a number greater than 1 that has no divisors other than 1 and itself.
For example: 2, 3, 5, 7, 11, 13, …

class Main {
    public static void main(String[] args) {
        int num = 41;  // Number to check if it's prime
        boolean isPrime = true;

        // If the number is less than or equal to 1, it's not prime
        if (num <= 1) {
            isPrime = false;
        } else {
            // Check divisibility from 2 to the square root of the number
            for (int i = 2; i <= Math.sqrt(num); i++) {
                if (num % i == 0) {
                    isPrime = false;
                    break;  // No need to check further if a divisor is found
                }
            }
        }

        // Output the result
        if (isPrime) {
            System.out.println(num + " is a prime number.");
        } else {
            System.out.println(num + " is not a prime number.");
        }
    }
}

Input Initialization:
The number to check for primality is stored in num (41 in this example).
A boolean variable isPrime is initialized to true. This assumes the number is prime unless proven otherwise.

Quick Check for Non-Primes:
If the number is 1 or less, it’s not a prime number, and isPrime is set to false.

Quick Check for Non-Primes:
If the number is 1 or less, it’s not a prime number, and isPrime is set to false.

Result Output:
After the loop, the value of isPrime determines whether num is prime:
If isPrime is true, the program prints that num is a prime number.
Otherwise, it prints that num is not a prime number.

Example Execution
Input: num = 41
num is greater than 1, so the program proceeds to the loop.
The loop checks divisibility for i = 2 to sqrt(41) (~6.4).
41 % 2 != 0
41 % 3 != 0
41 % 4 != 0
41 % 5 != 0
41 % 6 != 0
Since no divisors are found, isPrime remains true.

Output:

41 is a prime number.