Vendor System
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**Project Title:**
Vendor Payment Management System Using Java (OOP)
**Project Description:**
I developed a Java program that demonstrates the use of **Object-Oriented Programming (OOP)** concepts to manage vendor contracts and calculate monthly payments based on different vendor types.
The system is structured using a **base class and subclasses** to represent different vendor categories.
**Vendor (Base Class – Superclass)**
This class represents a general vendor and contains the following private attributes:
* **vendorId**
* **vendorName**
* **baseContractAmount**
Validation rules are implemented in the setter methods:
* **vendorId** must start with `"VEND"`
* **vendorName** must contain at least **4 characters**
* **baseContractAmount** must be **greater than or equal to 10,000**
The class also includes a method:
* **calculateMonthlyPayment()** which returns the base contract amount as the default implementation.
**LocalVendor (Subclass)**
This class inherits from **Vendor** and overrides the **calculateMonthlyPayment()** method to:
* Add **12% tax** to the base contract amount
* Add a **fixed compliance fee of 500**
**InternationalVendor (Subclass)**
This class also inherits from **Vendor** and introduces an additional private attribute:
* **exchangeRate**
Validation rule:
* **exchangeRate** must be **greater than 0**
The **calculateMonthlyPayment()** method is overridden to:
* Convert the base amount using the **exchange rate**
* Add **18% customs duty**
* Add an **international handling fee of 2000**
**Main Class Functionality:**
The main class demonstrates **polymorphism** by using a **Vendor reference** to create objects from both **LocalVendor** and **InternationalVendor** classes, then calling the **calculateMonthlyPayment()** method for each vendor type.
**Concepts Used in the Project:**
* Inheritance
* Encapsulation
* Method Overriding
* Polymorphism
* Input validation in setters
* Object creation and method invocation in the main class
**Project Goal:**
The goal of this project is to practice and demonstrate key **OOP principles in Java** by building a simple system that calculates vendor payments based on different business rules for local and international vendors.