Checked vs Unchecked Exceptions in Java

Definition

Checked exceptions are exceptions that are checked at compile-time. The Java compiler requires that these exceptions be either handled using a try-catch block or declared in the method signature using the throws keyword.

Common Checked Exceptions

• IOException
• SQLException
• ClassNotFoundException

Example

import java.io.FileReader;
import java.io.IOException;

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

Definition

Unchecked exceptions are exceptions that are not checked at compile-time. They are subclasses of RuntimeException and can occur during the runtime of the program. The compiler does not require these exceptions to be handled or declared.

Common Unchecked Exceptions

• NullPointerException
• ArrayIndexOutOfBoundsException
• IllegalArgumentException

Example

public class UncheckedExceptionExample {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3};
        System.out.println(numbers[5]); // This will throw ArrayIndexOutOfBoundsException
    }
}
                

Key Takeaways

• Always handle checked exceptions to prevent application crashes.
• Use custom exceptions to provide more meaningful error messages.
• Avoid catching generic Exception or Throwable unless necessary.
• Document the exceptions that your methods can throw.
• Use try-with-resources for automatic resource management.