Java Handle Related Failures Without Hiding Differences

Understand the idea

Catch more specific exception types before broader ones so a general handler does not make a later specific handler unreachable. In a multi-catch, the listed alternatives cannot have a subtype relationship that makes one redundant. A finally block runs during normal completion and many exceptional exits, but it is not a guarantee against process termination or machine failure.

Run it locally

Use a local JDK 21 or newer. Save the complete example as Main.java in a separate lab folder, then compile and run it with the commands below. Java examples do not run in Bhylu’s browser playground. The -ea option enables assertion checks used by some lessons.

JDK and terminal setup

javac --release 21 -encoding UTF-8 -d out Main.java
java -ea -cp out Main

A worked example

public class Main {
    public static void main(String[] args) {
        try {
            int seats = Integer.parseInt("4");
            if (seats > 3) throw new IllegalArgumentException("capacity exceeded");
        } catch (IllegalArgumentException failure) {
            System.out.println("Invalid booking: " + failure.getMessage());
        } finally {
            System.out.println("Request finished");
        }
    }
}

Expected output

Invalid booking: capacity exceeded
Request finished

NumberFormatException is an IllegalArgumentException subtype, so this single handler covers both parse rejection and the explicit range rejection. That is a deliberate small example; a user interface might want different messages for those failures. Finally records completion without attempting to claim that the booking succeeded.