Sealed Class Hierarchy Design

public class SealedClassHierarchy {

    sealed interface Event permits LoginEvent, LogoutEvent, PurchaseEvent, ErrorEvent {
        long timestamp();
        String userId();
    }

    record LoginEvent(long timestamp, String userId, String ip) implements Event {
        @Override public long timestamp() { return timestamp; }
        @Override public String userId() { return userId; }
    }

    record LogoutEvent(long timestamp, String userId) implements Event {
        @Override public long timestamp() { return timestamp; }
        @Override public String userId() { return userId; }
    }

    record PurchaseEvent(long timestamp, String userId, String item, double amount) implements Event {
        @Override public long timestamp() { return timestamp; }
        @Override public String userId() { return userId; }
    }

    record ErrorEvent(long timestamp, String userId, String message) implements Event {
        @Override public long timestamp() { return timestamp; }
        @Override public String userId() { return userId; }
    }

    static String processEvent(Event event) {
        return switch (event) {
            case LoginEvent e -> "User " + e.userId() + " logged in from " + e.ip();
            case LogoutEvent e -> "User " + e.userId() + " logged out";
            case PurchaseEvent e -> "User " + e.userId() + " bought " + e.item() + " for $" + e.amount();
            case ErrorEvent e -> "Error for " + e.userId() + ": " + e.message();
        };
    }

    public static void main(String[] args) {
        Event[] events = {
            new LoginEvent(System.currentTimeMillis(), "alice", "192.168.1.1"),
            new PurchaseEvent(System.currentTimeMillis(), "alice", "Widget", 29.99),
            new ErrorEvent(System.currentTimeMillis(), "bob", "Invalid session"),
            new LogoutEvent(System.currentTimeMillis(), "alice")
        };

        for (Event event : events) {
            System.out.println(processEvent(event));
        }
    }
}