What is defensive programming?

💡 Concept: Defensive Programming

Defensive programming is a development approach focused on anticipating potential errors and writing code that handles unexpected conditions gracefully.

📘 Quick Intro

It involves validating inputs, handling exceptions carefully, and designing software to be resilient against misuse and failures.

🧠 Analogy

Think of defensive programming like building a car with multiple safety features to protect passengers during unforeseen events.

🔧 Technical Explanation

✅ Validate all external inputs to prevent invalid data processing.
✅ Use exceptions to catch and recover from unexpected errors.
✅ Avoid assumptions about the environment or other code behavior.
✅ Implement logging and monitoring for early detection of issues.
✅ Follow coding standards to improve maintainability and reduce bugs.

🎯 Use Cases

✅ Building mission-critical systems requiring high reliability.
✅ Designing APIs that handle invalid usage gracefully.
✅ Developing applications exposed to unpredictable input.
✅ Creating maintainable codebases for long-term projects.

💻 Code Example


public void ProcessOrder(Order order) {
    if (order == null) throw new ArgumentNullException(nameof(order));
    if (order.Items == null || order.Items.Count == 0) {
        throw new ArgumentException(""Order must have at least one item."");
    }
    try {
        // Process order
    }
    catch (Exception ex) {
        // Log and handle exception
        throw;
    }
}

❓ Interview Q&A

Q1: What is defensive programming?
A: Writing code that anticipates and handles errors proactively.

Q2: Why validate inputs?
A: To prevent invalid data from causing failures.

Q3: How does logging help?
A: It aids in troubleshooting and monitoring.

Q4: Should you catch all exceptions?
A: No, catch and handle expected exceptions specifically.

Q5: What role do coding standards play?
A: They reduce bugs and improve readability.

Q6: Can defensive programming impact performance?
A: Slightly, but improves reliability.

Q7: What is the difference between defensive and defensive programming?
A: Trick question; same meaning.

Q8: How to handle unexpected inputs?
A: Validate and sanitize inputs.

Q9: Is defensive programming only for beginners?
A: No, essential for all developers.

Q10: How to ensure maintainability?
A: Use clear, consistent defensive coding practices.

📝 MCQs

Q1. What is defensive programming?

Writing error-resistant code
Ignoring errors
Writing fast code
Using only try-catch

Q2. Why validate inputs?

To slow app
Prevent failures
Ignore inputs
Trust user input

Q3. How does logging help?

Hides bugs
Troubleshooting
Crashes app
Confuses users

Q4. Should you catch all exceptions?

Yes
No
Sometimes
Always

Q5. What role do coding standards play?

Increase bugs
Reduce bugs
No effect
Make code slower

Q6. Can defensive programming impact performance?

No
Slightly
Always
Never

Q7. How to handle unexpected inputs?

Ignore
Validate and sanitize
Crash app
Log only

Q8. Is defensive programming only for beginners?

Yes
No
Maybe
Never

Q9. How to ensure maintainability?

Random code
Consistent practices
Ignore errors
Complex code

Q10. What is the main goal of defensive programming?

Fast code
Robust code
Minimal code
Buggy code

💡 Bonus Insight

Defensive programming helps create software that is easier to debug, maintain, and less prone to unexpected failures.

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