Sample of Java Pattern -- Observer

Appointment.java

package observer;

import java.util.Date;
import java.util.Observable;

public class Appointment extends Observable {
    private String host;
    private String guest;
    private Date appointmentDate;
    private int status;
    
    public Appointment(){}
    
    public String getHost() {
        return host;
    }

    public String getGuest() {
        return guest;
    }

    public Date getAppointmentDate() {
        return appointmentDate;
    }

    public int getStatus() {
        return status;
    }

    public void createAppointment(String host, String guest, Date appointmentDate){
        this.host = host;
        this.guest = guest;
        this.appointmentDate = appointmentDate;
        this.status = 0;
        setChanged();
        this.notifyObservers(this);
    }

    public void cancelAppointment(String host, String guest, Date appointmentDate){
        if(this.host != null && this.guest != null && this.appointmentDate != null && this.status != 1){
            this.status = 1;
            setChanged();
            this.notifyObservers(this);
        }
    }

}

EmailService.java

package observer;

import java.util.Observable;
import java.util.Observer;

public class EmailService implements Observer {
    private Observable observable;
    
    public EmailService(Observable observable){
        this.observable = observable;
        observable.addObserver(this);
    }
    
    public void update(Observable o, Object arg) {
        if(arg instanceof Appointment){
            Appointment appointment = (Appointment)arg;
            if(appointment.getStatus() ==0)
                System.out.println("send a creation email to host and guest");
            else
                System.out.println("send a cancellation email to host and guest");
        }
    }

}

SMSService.java

package observer;

import java.util.Observable;
import java.util.Observer;

public class SMSService implements Observer {
    private Observable observable;
    
    public SMSService(Observable observable){
        this.observable = observable;
        observable.addObserver(this);
    }
    
    public void update(Observable o, Object arg) {
        if(arg instanceof Appointment){
            Appointment appointment = (Appointment)arg;
            if(appointment.getStatus() ==0)
                System.out.println("send a creation sms to host and guest");
            else
                System.out.println("send a cancellation sms to host and guest");
        }
    }
}

ObserverTest.java

package observer;

import java.util.Date;

public class ObserverTest {

    public static void main(String[] args) {
        Appointment appointment = new Appointment();
        EmailService emailService = new EmailService(appointment);
        SMSService smsService = new SMSService(appointment);
        String host ="";
        String guest ="";
        Date appointmentDate = new Date();
        appointment.createAppointment(host, guest, appointmentDate);
        appointment.cancelAppointment(host, guest, appointmentDate);
    }

}

you may download the source code.