📘 Module 7: Access Modifiers & Packages

अब मैं आपको Access Modifiers और Packages का एक Real-World Java Project Example देकर समझाता हूँ, जैसे कि किसी कंपनी का “Online Shopping Application” बन रहा हो।

🛒 Real-World Example: Online Shopping System

🎯 Modules in Project:

1. com.shop.customers – Customer details
2. com.shop.products – Product details
3. com.shop.orders – Order management
4. com.shop.utils – Utility classes (Helper, Validator)

🔹 Package Structure:

com/
 └── shop/
     ├── customers/
     │    └── Customer.java
     ├── products/
     │    └── Product.java
     ├── orders/
     │    └── Order.java
     └── utils/
          └── Validator.java

🔐 Access Modifier Usage:

✅ 1. private → Data hiding

// Customer.java
package com.shop.customers;

public class Customer {
    private String name;        // Can't be accessed directly outside
    private String email;

    public void setName(String name) { this.name = name; }
    public String getName() { return name; }
}

➡️ इस तरह name और email की direct access रोकी गई — Encapsulation + Security

✅ 2. protected → Allow subclass access

// Product.java
package com.shop.products;

public class Product {
    protected double discount = 0.05;

    protected void applyDiscount() {
        System.out.println("5% discount applied");
    }
}

➡️ अब कोई subclass जैसे SpecialProduct इसको access कर सकता है।

✅ 3. default (no modifier) → Package-private access

// Validator.java
package com.shop.utils;

class Validator {
    static boolean validateEmail(String email) {
        return email.contains("@");
    }
}

➡️ ये method सिर्फ उसी package (com.shop.utils) में usable है।

✅ 4. public → Universal access

// Order.java
package com.shop.orders;

public class Order {
    public int orderId;
    public void placeOrder() {
        System.out.println("Order placed successfully");
    }
}

➡️ इसे कोई भी package import करके use कर सकता है।

🧠 जब आप Main Program लिखते हैं:

// Main.java
import com.shop.customers.Customer;
import com.shop.orders.Order;

public class Main {
    public static void main(String[] args) {
        Customer c = new Customer();
        c.setName("Kaunain");
        System.out.println(c.getName());

        Order o = new Order();
        o.placeOrder();
    }
}

✅ Summary: Real Use of Modifiers

🎁 Bonus Tip: Naming Convention