VAT Calculator Application

A Java Swing-based graphical user interface application for calculating Value Added Tax (VAT) charges on services.

Overview

This application provides a user-friendly GUI to:

• Select a service from a predefined list
• Enter a charge amount
• Automatically calculate VAT based on the service's VAT rate
• Display VAT amount and total charge (charge + VAT)

Features

• Service Selection: Choose from multiple services with different VAT rates
• VAT Calculation: Automatic calculation based on service VAT rate (0%, 5%, or 20%)
• Input Validation: Ensures valid service codes and positive charge amounts
• Clear Interface: Modern, intuitive GUI with clear labels and results display
• Error Handling: User-friendly error messages for invalid inputs

Project Structure

Lab6/
├── VATRate.java          # Enum defining VAT rates (ZERO, LOW, STANDARD)
├── Service.java          # Service class with code, name, and VAT rate
├── Charge.java           # Charge class that calculates VAT for a service
├── VATCalculatorGUI.java # Main GUI application
└── README.md             # This file

Classes

VATRate

Enumeration representing different VAT rates:

• ZERO (0%)
• LOW (5%)
• STANDARD (20%)

Service

Represents a service with:

• Code: Must follow format AAAA99999 (4 uppercase letters + 5 digits)
• Name: Service description
• Rate: VAT rate applicable to the service

Charge

Represents a charge for a service:

• Validates that service is not null
• Validates that charge amount is positive
• Calculates VAT amount based on service's VAT rate

VATCalculatorGUI

Main Swing GUI application that provides:

• Service selection dropdown
• Charge amount input field
• Calculate and Clear buttons
• Results display showing VAT amount and total

Requirements

• Java JDK 8 or higher
• Java Swing (included in JDK)

How to Compile

From the javaLabs directory:

javac Lab6/*.java

Or from within the Lab6 directory:

javac *.java

How to Run

From the javaLabs directory:

java Lab6.VATCalculatorGUI

Or from within the Lab6 directory:

java VATCalculatorGUI

Usage

1. Select a Service: Choose a service from the dropdown menu

   • The current VAT rate for the selected service will be displayed

2. Enter Charge Amount: Type a positive number in the charge amount field

3. Calculate: Click the "Calculate VAT" button

   • VAT amount will be calculated and displayed
   • Total amount (charge + VAT) will be shown

4. Clear: Click "Clear" to reset all fields and start over

Example Services

The application comes with sample services:

• Book Sales (BOOK12345) - 0% VAT
• Food Service (FOOD12345) - 5% VAT
• Consulting (CONS12345) - 20% VAT
• Software License (SOFT12345) - 20% VAT
• Medical Equipment (MEDI12345) - 0% VAT

VAT Calculation Formula

VAT Amount = Charge Amount × (VAT Rate / 100)
Total Amount = Charge Amount + VAT Amount

Error Handling

The application handles various error cases:

• Invalid service code format
• Null or empty service
• Non-positive charge amounts
• Invalid number format in charge field
• Missing input fields

Code Quality

• Comprehensive JavaDoc comments
• Input validation
• Error handling with user-friendly messages
• Clean, maintainable code structure
• Modern Swing GUI design

Author

Lab6

License

This project is for educational purposes.