Example: Print Prime Numbers in a Range in Java

// Print 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 the number
        // If a number has a divisor greater than its square root, it must also have a divisor smaller than its square root.
        for (int i = 2; i * i <= num; i++) {
            if (num % i == 0) {
                return false; // If divisible, it's not prime
            }
        }
        return true; // If no divisors found, 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 to enter the start and end of the range
        System.out.print("Enter the starting number of the range: ");
        int start = scanner.nextInt();

        System.out.print("Enter the ending number of the range: ");
        int end = scanner.nextInt();

        // Step 3: Validate the input range
        if (start > end || start < 0) {
            System.out.println("Invalid range. Start number must be less than or equal to end number and non-negative.");
            scanner.close();
            return;
        }

        // Step 4: Print a message indicating the prime numbers found
        System.out.println("Prime numbers between " + start + " and " + end + " are:");

        // Step 5: Iterate through the range and check each number for primality
        for (int i = start; i <= end; i++) {
            if (isPrime(i)) {
                System.out.print(i + " ");
            }
        }
        System.out.println(); // For a new line at the end

        // Step 6: Close the scanner
        scanner.close();
    }
}