Difference between checked and unchecked exceptions in Java

💡 Concept: Checked vs Unchecked Exceptions

Java exceptions are divided into checked and unchecked based on whether the compiler forces exception handling.

📘 Quick Intro

Checked exceptions must be either caught or declared in the method signature; unchecked exceptions do not require explicit handling.

🧠 Analogy

Think of checked exceptions as mandatory warnings you must address, like a fire alarm, while unchecked exceptions are unexpected breakdowns that might crash your system if unhandled.

🔧 Technical Explanation

Checked exceptions extend Exception but not RuntimeException.
Unchecked exceptions extend RuntimeException.
Checked exceptions require try-catch or throws declaration.
Unchecked exceptions can be ignored or handled optionally.
Errors are a separate category, generally unrecoverable.

🎯 Use Cases

✅ Checked exceptions: recoverable conditions (e.g., IOException).
✅ Unchecked exceptions: programming errors (e.g., NullPointerException).
✅ Design APIs to clearly indicate exception handling.

💻 Java Exception Example


public void readFile(String filename) throws IOException {
    FileReader file = new FileReader(filename);
    // IOException is checked, must declare or catch
}

public void divide(int a, int b) {
    int result = a / b; // ArithmeticException unchecked
}

❓ Interview Q&A

Q1: What is a checked exception?
A: Exception checked at compile time requiring handling.

Q2: What is an unchecked exception?
A: Exception not checked at compile time.

Q3: Are Errors checked or unchecked?
A: Neither, they indicate serious problems.

Q4: How to handle checked exceptions?
A: Try-catch or throws.

Q5: Can unchecked exceptions be caught?
A: Yes, optionally.

Q6: Example of checked exception?
A: IOException.

Q7: Example of unchecked exception?
A: NullPointerException.

Q8: Is it mandatory to declare unchecked exceptions?
A: No.

Q9: Difference between Exception and Error?
A: Exception is recoverable, Error is not.

Q10: Can RuntimeException be a checked exception?
A: No.

📝 MCQs

Q1. What is a checked exception?

Unchecked exception
Checked exception
Error
RuntimeException

Q2. What is an unchecked exception?

Checked exception
Unchecked exception
Error
Throwable

Q3. Are Errors checked or unchecked?

Checked
Unchecked
Neither
Both

Q4. How to handle checked exceptions?

Ignore
Try-catch or throws
Only throws
Only try-catch

Q5. Can unchecked exceptions be caught?

No
Yes
Only checked exceptions
Never

Q6. Example of checked exception?

NullPointerException
IOException
ArithmeticException
Error

Q7. Example of unchecked exception?

IOException
NullPointerException
FileNotFoundException
SQLException

Q8. Is it mandatory to declare unchecked exceptions?

Yes
No
Sometimes
Depends

Q9. Difference between Exception and Error?

Both recoverable
Exception is recoverable, Error is not
Both unrecoverable
None

Q10. Can RuntimeException be a checked exception?

Yes
No
Sometimes
Only in Java 9+

💡 Bonus Insight

Understanding checked vs unchecked exceptions improves error handling and software robustness.

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