Example: Prime Numbers in a Range in Java

// Prime Numbers in a Range
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {

    // Method to check if a number is prime
    public static boolean isPrime(int num) {
        if (num <= 1) {
            return false; // Numbers less than or equal to 1 are not prime
        }
        // Check for divisibility from 2 up to the square root of num
        // We only need to check up to sqrt(num) because if a number n has a divisor
        // greater than sqrt(n), it must also have a divisor smaller than sqrt(n).
        for (int i = 2; i * i <= num; i++) {
            if (num % i == 0) {
                return false; // Found a divisor, so it's not prime
            }
        }
        return true; // No divisors found, so it's prime
    }

    public static void main(String[] args) {
        // Step 1: Create a Scanner object to read user input
        Scanner scanner = new Scanner(System.in);

        // Step 2: Prompt the user for the lower bound
        System.out.print("Enter the lower bound of the range: ");
        int lowerBound = scanner.nextInt();

        // Step 3: Prompt the user for the upper bound
        System.out.print("Enter the upper bound of the range: ");
        int upperBound = scanner.nextInt();

        // Step 4: Validate the input range
        if (lowerBound > upperBound) {
            System.out.println("Error: Lower bound cannot be greater than upper bound.");
            scanner.close();
            return;
        }

        // Step 5: Print a header for the output
        System.out.println("Prime numbers between " + lowerBound + " and " + upperBound + " are:");

        // Step 6: Iterate through the range and check for prime numbers
        for (int i = lowerBound; i <= upperBound; i++) {
            if (isPrime(i)) {
                System.out.print(i + " ");
            }
        }
        System.out.println(); // Print a newline for better formatting

        // Step 7: Close the scanner to release system resources
        scanner.close();
    }
}