Main.java

public class Main {
    public static void main(String[] args) {

        System.out.println("========================================");
        System.out.println("  Student Product Billing & Management  ");
        System.out.println("========================================\n");

        // US-01: Student Object
        System.out.println(">>> US-01: Student Object Creation <<<");
        Student student1 = new Student();
        student1.rollNo = 101;
        student1.name   = "Aarav Sharma";
        student1.marks  = 88.5;
        student1.displayDetails();

        // US-02: String Formatting
        System.out.println("\n>>> US-02: String Formatting <<<");
        student1.displayNameFormats();

        // US-03: Marks Array
        System.out.println("\n>>> US-03: Marks Array of 5 Students <<<");
        double[] marksArray = {85.5, 90.0, 78.0, 92.5, 88.0};
        for (int i = 0; i < marksArray.length; i++) {
            System.out.println("Student " + (i + 1) + " Marks: " + marksArray[i]);
        }
        double total = 0;
        for (int i = 0; i < marksArray.length; i++) { total += marksArray[i]; }
        System.out.println("Average Marks: " + (total / marksArray.length));

        // US-04: Method Overloading
        System.out.println("\n>>> US-04: Product Billing (Method Overloading) <<<");
        ProductBilling billing = new ProductBilling();
        double bill1 = billing.calculateBill(500.0);
        System.out.println("Total Bill (1 product)  : Rs. " + bill1);
        double bill2 = billing.calculateBill(500.0, 300.0);
        System.out.println("Total Bill (2 products) : Rs. " + bill2);
        double bill3 = billing.calculateBill(500.0, 300.0, 200.0);
        System.out.println("Total Bill (3 products) : Rs. " + bill3);
        System.out.println("After 10% Discount      : Rs. " + billing.applyDiscount(bill3, 10));

        // US-05 & US-06: Employee
        System.out.println("\n>>> US-05 & US-06: Employee with Constructor and Static <<<");
        Employee emp1 = new Employee(201, "Riya Gupta", 55000.0);
        emp1.displayDetails();
        System.out.println();
        Employee emp2 = new Employee(202, "Rahul Verma", 62000.0);
        emp2.displayDetails();

        // US-07: Encapsulation
        System.out.println("\n>>> US-07: Product with Encapsulation <<<");
        Product product = new Product();
        product.setProductId(301);
        product.setProductName("Java Programming Book");
        product.setPrice(450.0);
        product.displayProduct();

        // US-08: Inheritance
        System.out.println("\n>>> US-08: Inheritance - CollegeStudent <<<");
        CollegeStudent cStudent = new CollegeStudent();
        cStudent.rollNo      = 501;
        cStudent.name        = "Priya Singh";
        cStudent.marks       = 91.0;
        cStudent.collegeName = "Delhi Tech College";
        cStudent.course      = "B.Tech CSE";
        cStudent.displayCollegeDetails();

        System.out.println("\n========================================");
        System.out.println("         Program Completed!              ");
        System.out.println("========================================");
    }
}