Java Exceptions Explained – Checked vs Unchecked Exceptions with Examples and Best Practices

Introduction to Exceptions in Java

In Java, exceptions are events that disrupt the normal flow of a program. They help handle runtime errors gracefully without crashing the entire application. Proper exception handling is critical for building robust, fault-tolerant software.

Java categorizes exceptions into two main types:

• Checked Exceptions – Verified at compile-time.
• Unchecked Exceptions – Verified at runtime.

Understanding their differences and use cases ensures you design stable, maintainable code.

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What Are Checked Exceptions?

Checked exceptions are compile-time exceptions. The compiler forces you to handle or declare them using try-catch or throws.

✅ Examples:

• IOException
• SQLException
• ClassNotFoundException

import java.io.*;

public class CheckedExample {
    public static void main(String[] args) {
        try {
            FileReader fr = new FileReader("file.txt"); // Checked exception
        } catch (IOException e) {
            System.out.println("File not found: " + e.getMessage());
        }
    }
}

🔑 Key Points:

• Must be handled or declared.
• Represent recoverable situations.
• Commonly used in I/O, database, and network operations.

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What Are Unchecked Exceptions?

Unchecked exceptions are runtime exceptions. They are not checked at compile-time and usually indicate programming errors.

✅ Examples:

• NullPointerException
• ArrayIndexOutOfBoundsException
• ArithmeticException

public class UncheckedExample {
    public static void main(String[] args) {
        int num = 10 / 0; // ArithmeticException
    }
}

🔑 Key Points:

• No mandatory handling.
• Represent programming logic errors.
• Should be prevented via proper validation.

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Comparison: Checked vs Unchecked Exceptions

Feature	Checked Exceptions	Unchecked Exceptions
Compile-time checking	Yes	No
Must be declared/handled	Required	Optional
Common examples	IOException, SQLException	NullPointerException, ArithmeticException
Represents	Recoverable errors	Programming bugs
Package	java.lang.Exception	java.lang.RuntimeException

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Real-World Analogy

• Checked Exceptions: Like a bank transaction – the system forces you to confirm the account, amount, and authorization before proceeding.
• Unchecked Exceptions: Like forgetting your wallet – it's not verified upfront, but when you need to pay, the issue arises.

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Best Practices

• ✅ Use checked exceptions for expected, recoverable conditions.
• ✅ Use unchecked exceptions for programming errors.
• ✅ Never swallow exceptions silently. Always log them.
• ✅ Create custom exceptions only when it adds clarity.
• ❌ Avoid overusing checked exceptions; too many throws reduce readability.

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Common Mistakes

• ❌ Catching generic Exception everywhere.
• ❌ Using unchecked exceptions for business logic.
• ❌ Ignoring exception messages/logging.

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Performance Considerations

• Frequent exception throwing can impact performance.
• Avoid using exceptions for flow control.
• Unchecked exceptions are slightly faster because they skip compile-time checking.

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Interview Questions & Answers

Q1. Difference between checked and unchecked exceptions?
A: Checked are compile-time, must be handled; unchecked are runtime and optional to handle.

Q2. Can you create custom checked exceptions?
A: Yes, by extending Exception.

Q3. Why prefer unchecked exceptions for programming errors?
A: They indicate bugs that should be fixed, not recovered from.

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Java Version Relevance

• Java 7: Introduced multi-catch for better exception handling.
• Java 8: try-with-resources improved checked exception management.

Java Version	Feature Change
Java 7	Multi-catch block
Java 8	try-with-resources enhancement

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Conclusion & Key Takeaways

• Use checked exceptions for recoverable conditions.
• Use unchecked exceptions for programming errors.
• Proper handling leads to robust and maintainable Java applications.