Example: Optimized Prime Number Check in Java

// Optimized Prime Number Check
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int number = scanner.nextInt();

        boolean isPrime = true;

        if (number <= 1) {
            isPrime = false;
        } else {
            // Loop from 2 up to the square root of the number
            // We cast Math.sqrt(number) to int because loop counter is int
            for (int i = 2; i * i <= number; i++) { // Equivalent to i <= Math.sqrt(number)
                if (number % i == 0) {
                    isPrime = false;
                    break;
                }
            }
        }

        if (isPrime) {
            System.out.println(number + " is a prime number.");
        } else {
            System.out.println(number + " is not a prime number.");
        }

        scanner.close();
    }
}