Solution: The Flight Boarding Protocol

// 1. Checked Exception (Must be handled or declared)
class PassportExpiredException extends Exception {}
// 2. Unchecked Exception (Runtime failure, stops flow implicitly)
class SecurityAlertException extends RuntimeException {}
public class BoardingSystem {
    public static void tryBoarding(String status) {
        try {
            checkPassenger(status);
        } catch (PassportExpiredException e) {
            // Recoverable: We handle this and continue
            System.out.println("Recovery: Refer to service desk.");
        }
        // We do NOT catch SecurityAlertException here; it crashes the app as intended.
    }
    // We must declare 'throws PassportExpiredException' because it is Checked
    public static void checkPassenger(String status) throws PassportExpiredException { 
        if (status.equals("Expired")) {
            throw new PassportExpiredException();
        } else if (status.equals("Banned")) {
            throw new SecurityAlertException();
        } else {
            System.out.println("Boarding successful.");
        }
    }
    public static void main(String[] args) {
        // Test 1: Handle recoverable error
        System.out.println("--- Passenger 1: Expired Passport ---");
        tryBoarding("Expired");
        // Test 2: Handle critical error (Should crash the program)
        System.out.println("\n--- Passenger 2: Security Risk ---");
        tryBoarding("Banned");
    }
}