Example: Maximum Handshakes Calculator (Iterative) in Java

// Maximum Handshakes Calculator (Iterative)
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the number of people: ");
        int numberOfPeople = scanner.nextInt();

        if (numberOfPeople < 0) {
            System.out.println("Number of people cannot be negative.");
        } else if (numberOfPeople <= 1) { // 0 or 1 person results in 0 handshakes
            System.out.println("Maximum number of handshakes: 0");
        } else {
            long maxHandshakes = 0;
            // The first person shakes hands with (n-1) others.
            // The second person shakes hands with (n-2) new others (excluding the first).
            // ... and so on, until the last person has no new hands to shake.
            for (int i = 1; i < numberOfPeople; i++) {
                maxHandshakes += i;
            }
            System.out.println("Maximum number of handshakes: " + maxHandshakes);
        }
        scanner.close();
    }
}