Difference Between Checked and Unchecked Exceptions in Java

1. Introduction

In Java, exceptions are categorized into two main types:

• Checked Exceptions
• Unchecked Exceptions

The key difference lies in when they are checked (compile-time vs runtime) and how they are handled.

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2. Checked Exceptions

Explanation

• Checked exceptions are checked at compile-time.

• The compiler forces you to handle them using:

  • try-catch block OR
  • throws keyword

• These exceptions represent recoverable conditions.

Common Examples

• IOException
• SQLException
• FileNotFoundException

Example

import java.io.FileReader;

public class CheckedExample {
    public static void main(String[] args) {
        try {
            FileReader fr = new FileReader("test.txt");
        } catch (Exception e) {
            System.out.println("File not found");
        }
    }
}

Explanation of Code

• FileReader may throw FileNotFoundException.
• Compiler forces handling using try-catch.
• Without handling → compilation error.

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3. Unchecked Exceptions

Explanation

• Unchecked exceptions are checked at runtime, not at compile-time.
• The compiler does NOT force you to handle them.
• They usually occur due to programming mistakes.

Common Examples

• NullPointerException
• ArithmeticException
• ArrayIndexOutOfBoundsException

Example

public class UncheckedExample {
    public static void main(String[] args) {
        int a = 10 / 0;
        System.out.println(a);
    }
}

Explanation of Code

• Division by zero causes ArithmeticException.
• Compiler allows it, but error occurs at runtime.

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4. Key Differences Table

Feature	Checked Exceptions	Unchecked Exceptions
Checked At	Compile-time	Runtime
Handling Required	Yes (Mandatory)	No (Optional)
Parent Class	Exception (excluding RuntimeException)	RuntimeException
Cause	External issues (I/O, DB)	Programming errors
Example	IOException	NullPointerException

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5. Code Comparison

// Checked Exception
import java.io.*;

class Test {
    void readFile() throws IOException {
        FileReader fr = new FileReader("abc.txt");
    }
}

// Unchecked Exception
class Test2 {
    void divide() {
        int x = 10 / 0;
    }
}

Explanation

• readFile() must declare throws IOException → Checked
• divide() compiles fine but fails at runtime → Unchecked

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6. When to Use What?

• Use Checked Exceptions when:

  • The error is recoverable
  • You want the caller to handle it

• Use Unchecked Exceptions when:

  • The error is due to logic mistakes
  • It cannot be reasonably recovered

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7. Summary

• Checked Exceptions → Compile-time, must handle
• Unchecked Exceptions → Runtime, optional handling
• Checked = predictable & recoverable
• Unchecked = programming errors

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