Module 2 Guided Project
Debugging Subscribe and Save Application
In this guided project, you'll learn how to apply debugging techniques to identify and fix issues in a subscription-based application. You'll practice using breakpoints, inspecting variables, and stepping through code execution.
The Scientific Method for Debugging
In this project, we'll apply the scientific method to systematically debug a Subscribe and Save application:
- Reproduce the bug with a small, repeatable test case
- Study the available data including error messages, logs, and stack traces
- Form a hypothesis about what might be causing the issue
- Experiment to test your hypothesis
- 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;
}Project Steps
-
Set up the debugging environment
Clone the project repository and configure your IDE's debugging tools. Make sure you're comfortable with setting breakpoints and stepping through code.
-
Understand the application structure
Review the codebase to understand how the Subscribe and Save application works. Pay particular attention to the inventory management system and order processing logic.
-
Identify the reported issues
Read through the reported bugs and reproduce them with simple test cases. Take note of the expected vs. actual behavior.
-
Set strategic breakpoints
Place breakpoints at key locations in the code where you suspect the issues might be occurring. Focus on inventory update methods and order processing logic.
-
Debug using the scientific method
Run the application in debug mode, inspect variables, and step through code execution. Form hypotheses about what's causing each issue and test them systematically.
-
Fix the identified bugs
Implement fixes for each bug you identify. Be sure to document what you changed and why.
-
Verify your fixes
Re-run the application with your test cases to ensure your fixes resolved the issues. Also test other functionality to ensure you haven't introduced new bugs.