Section 5: Exception Handling

Lesson 1: Understanding Exceptions in Java

1.1 Checked vs. Unchecked Exceptions

Exceptions in Java are divided into two categories: checked and unchecked.

Checked Exceptions: These are exceptions that the compiler forces you to handle. They are subclasses of Exception (excluding RuntimeException and its subclasses).

Unchecked Exceptions: These are exceptions that the compiler does not force you to handle. They are subclasses of RuntimeException.

1.2 Handling Exceptions Using try, catch, finally Blocks

Exception handling in Java involves the use of try, catch, and finally blocks.

Example (Handling Checked Exception):

import java.io.FileReader;

import java.io.IOException;

public class CheckedExceptionExample {

    public static void main(String[] args) {

        try {

            // Code that may throw a checked exception

            FileReader fileReader = new FileReader("example.txt");

            // Continue with other operations

        } catch (IOException e) {

            // Handle the exception

            System.out.println("An error occurred: " + e.getMessage());

        } finally {

            // Code in this block is executed whether an exception occurs or not

            System.out.println("Finally block executed.");

        }

    }

}

Example (Handling Unchecked Exception):

public class UncheckedExceptionExample {

    public static void main(String[] args) {

        try {

            // Code that may throw an unchecked exception

            int result = 5 / 0;

            // The following code will not be executed if an exception occurs above

            System.out.println("Result: " + result);

        } catch (ArithmeticException e) {

            // Handle the exception

            System.out.println("Division by zero: " + e.getMessage());

        } finally {

            System.out.println("Finally block executed.");

        }

    }

}

Lesson 2: Custom Exception Classes

2.1 Creating and Using Custom Exception Classes

You can create custom exception classes by extending the Exception class or one of its subclasses.

Example (Custom Exception):

// Custom exception class

class CustomException extends Exception {

    public CustomException(String message) {

        super(message);

    }

}

public class CustomExceptionExample {

    public static void main(String[] args) {

        try {

            // Throwing a custom exception

            throw new CustomException("This is a custom exception.");

        } catch (CustomException e) {

            // Handling the custom exception

            System.out.println("Caught custom exception: " + e.getMessage());

        }

    }

}

Creating custom exceptions allows you to define and handle specific error scenarios in your application.

Exception handling is a critical aspect of writing robust and reliable Java code. Understanding the types of exceptions, handling them appropriately, and creating custom exceptions when needed contribute to the stability of your applications. Practice these examples to master exception handling in Java.