Module 2 Guided Project

The Scientific Method for Debugging

In this project, we'll apply the scientific method to systematically debug a Subscribe and Save application:

1. Reproduce the bug with a small, repeatable test case
2. Study the available data including error messages, logs, and stack traces
3. Form a hypothesis about what might be causing the issue
4. Experiment to test your hypothesis
5. Repeat steps 2-4 until you've localized and fixed the bug

Bookstore Application Overview

We're working on a Bookstore application, focusing on the code that handles book deliveries, book orders, and checks on a particular title's quantity in stock. Our employees have reported a few odd behaviors of the system, so we want to check it out!

The key classes you'll be working with include:

• StoreInventory: Contains current inventory of books
• InventoryEntry: Represents current inventory of a single book

Debugging Techniques We'll Use

• IDE Debugger: We'll set breakpoints at strategic locations to pause execution and examine program state
• Variable Inspection: We'll inspect variable values during program execution to identify inconsistencies
• Step Execution: We'll step through the code line by line to understand how it's being executed
• Code Reading: We'll carefully examine the code to identify logical errors
• Regression Testing: After fixing bugs, we'll verify the fixes don't introduce new issues

Example Bug: Incorrect Order Processing

// Sample code with a bug
public boolean processOrder(String bookTitle, int quantity) {
    // Check if we have enough books in stock
    if (hasInventory(bookTitle, quantity)) {
        // Bug: This line doesn't actually update the inventory!
        // It should be: removeInventory(bookTitle, quantity);
        checkInventory(bookTitle);
        
        // Create and save the order
        Order order = new Order(bookTitle, quantity);
        orderRepository.save(order);
        return true;
    }
    return false;
}