Code Review Exercises That Actually Work: Java Edition (Junior to Senior)

In Part 1 of this series, we explored a practical, respectful approach to engineering interviews - focusing on real-world skills like code reviews, GitHub project walkthroughs, and collaborative coding.

In this post, we'll dive deeper into the code review portion of the interview. You'll get:

• A neutral Java code style guide to use during interviews
• Three code review examples, tailored for junior, mid-level, and senior candidates
• Tips for interviewers on how to run this part effectively

---

Why Code Reviews Belong in Interviews

Code reviews aren't just about syntax or formatting. They uncover how a candidate:

• Thinks about design and readability
• Communicates technical feedback
• Prioritizes bugs, maintainability, and best practices
• Balances tradeoffs and pragmatism

It's one of the most real-world ways to assess software engineers - and works across all levels of experience.

---

Java Style Guide for Code Review Exercises

This is a neutral guide to share with candidates during the exercise. It helps structure their review without giving away the "answers."

✅ Code Style & Structure

• Use descriptive class and method names
• Break down large methods into smaller, testable pieces
• Follow consistent indentation and spacing

🔐 Exception Handling

• Catch only specific exceptions
• Don't suppress or swallow errors silently

🧼 Clean Code

• Remove unnecessary code or comments
• Use named constants instead of magic numbers/strings
• Avoid duplicating logic

🔍 Input & Output

• Minimize direct System.out.println()
• Separate core logic from I/O when possible

🚦 Testability

• Make code easy to unit test
• Aim for pure functions and clear input/output boundaries

---

Junior-Level Code Review Example

Code Snippet:

public class UserDataProcessor {
    public static void process(String[] args) {
        for (int i = 0; i < args.length; i++) {
            String s = args[i];
            if (s.contains("@")) {
                System.out.println("Email: " + s);
            } else {
                try {
                    int n = Integer.parseInt(s);
                    System.out.println("Number: " + (n * 2));
                } catch (Exception e) {
                    System.out.println("Other: " + s);
                }
            }
        }
    }
}

What to Look For:

• Vague method name (process)
• Overuse of System.out.println()
• Poor exception handling (catch (Exception e))
• No input validation or testability

Optional Follow-up Prompt:

Now refactor the code to improve clarity and maintainability. Feel free to break it into smaller methods and add input validation.

---

Mid-Level Code Review Example

Code Snippet:

public class FileLogger {
    public void logMessage(String level, String message) {
        try {
            FileWriter writer = new FileWriter("log.txt", true);
            writer.write(level + ": " + message + "\n");
            writer.close();
        } catch (IOException e) {
            // ignore
        }
    }
}

What to Look For:

• No resource management (FileWriter should use try-with-resources)
• Swallowed exception with no logging or rethrow
• No separation between formatting and writing
• Hardcoded file path

Follow-up Prompt:

Refactor this to follow SOLID principles and Java best practices. Consider testability and error handling.

---

Senior-Level Code Review Example

Code Snippet:

public class NotificationService {
    private List<User> users;

    public void notifyUsers(String message) {
        for (User user : users) {
            if (user.getEmail() != null) {
                EmailSender.send(user.getEmail(), message);
            }
        }
    }
}

What to Look For:

• Tight coupling to EmailSender (static call)
• No abstraction/interface for notification method
• No error handling or delivery guarantees
• No logging or observability
• Threading/scalability not considered

Follow-up Prompt:

Refactor this to support future extensions (e.g., SMS, push notifications). Discuss design tradeoffs and test strategy.

---

Tips for Interviewers

• Use open-ended prompts after the review:
  • What would you change first?
  • Is this code testable? Why or why not?
  • Would this scale in a production system?
• Match the complexity to the candidate's level
• Don't judge by what they missed - focus on how they think, communicate, and justify decisions

---

Coming Up Next: Python, JavaScript, and More

This is just the beginning. Future posts will bring code review examples in other languages, helping teams run more effective interviews regardless of tech stack.

Comments

[Ghost Engineer]

try this if you get stuck during the interview. its an AI co-pilot that solves the questions for you so you can focus on the more important part of the interview, the communication part. its also a really good study tool: ghostengineer.com