Chained Exceptions

 Chained exceptions, also known as nested exceptions, allow you to associate one exception with another. This feature is useful when you want to provide more context or information about the cause of an exception. In Java, you can chain exceptions using constructors that take a `Throwable` (or its subclasses) as an argument.

Syntax:

try {

    // Code that may throw an exception

} catch (ExceptionType1 e1) {

    throw new ExceptionType2("Additional information", e1);

}

Explanation:

- Inside a `catch` block, you can create a new exception object and pass the original exception (`e1`) as the cause.

- The chained exception (`ExceptionType2`) includes a message and the original exception (`e1`) as its cause.

- This technique allows you to preserve the original exception's stack trace and context while providing additional information about the higher-level exception.

- Chained exceptions can be caught and processed at higher levels of the call stack, allowing for better error handling and debugging.

Example:

public class ChainedExceptionsExample {

    public static void main(String[] args) {

        try {

            processFile("nonexistent.txt");

        } catch (FileProcessingException e) {

            System.out.println("Error processing file: " + e.getMessage());

            System.out.println("Root cause: " + e.getCause().getMessage());

        }

    }

    public static void processFile(String filename) throws FileProcessingException {

        try {

            readFile(filename);

        } catch (FileNotFoundException e) {

            throw new FileProcessingException("File not found", e);

        }

    }

    public static void readFile(String filename) throws FileNotFoundException {

        // Simulate file reading (throws FileNotFoundException if file not found)

        throw new FileNotFoundException("File not found: " + filename);

    }

}

class FileProcessingException extends Exception {

    public FileProcessingException(String message, Throwable cause) {

        super(message, cause);

    }

}

In this example, the `processFile` method catches a `FileNotFoundException` and rethrows it as a `FileProcessingException` with the original exception as the cause. When the exception is caught in the `main` method, it prints both the custom message and the root cause of the exception.

Analogy:

Imagine you are debugging a complex system with multiple layers of code. Each layer of code represents a floor in a building. If a problem occurs on a higher floor (e.g., file not found), you want to provide information about both the current floor (the specific error message) and the ground floor (the root cause or original problem). Chained exceptions act like an elevator that can take you from the current floor to the ground floor, allowing you to trace back the root cause of the problem.