Example: Friendly Pair Checker in Java

// Friendly Pair Checker
import java.util.Scanner;

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

    // Method to calculate the sum of proper divisors of a number
    public static int sumProperDivisors(int num) {
        if (num <= 1) {
            return 0; // Proper divisors are not defined for numbers <= 1, or sum is 0
        }
        int sum = 1; // 1 is always a proper divisor
        for (int i = 2; i * i <= num; i++) {
            if (num % i == 0) {
                sum += i;
                if (i * i != num) { // If i*i == num, i is counted only once
                    sum += num / i;
                }
            }
        }
        return sum;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Step 1: Get input from the user
        System.out.print("Enter the first number: ");
        int num1 = scanner.nextInt();

        System.out.print("Enter the second number: ");
        int num2 = scanner.nextInt();

        // Step 2: Validate input
        if (num1 <= 0 || num2 <= 0) {
            System.out.println("Numbers must be positive integers.");
            scanner.close();
            return;
        }

        // Step 3: Calculate the sum of proper divisors for both numbers
        int sumDivisors1 = sumProperDivisors(num1);
        int sumDivisors2 = sumProperDivisors(num2);

        // Step 4: Check if they form a friendly pair
        // A friendly pair consists of two DIFFERENT numbers
        if (num1 != num2 && sumDivisors1 == num2 && sumDivisors2 == num1) {
            System.out.println(num1 + " and " + num2 + " form a friendly pair.");
        } else {
            System.out.println(num1 + " and " + num2 + " do not form a friendly pair.");
        }

        scanner.close();
    }
}