ObserverPattern

1. Class Main.java

package designpattern.observer;

import designpattern.observer.MyModel.Person;

public class Main
{

    public static void main(String[] args)
    {
        MyModel model = new MyModel();
        MyObserver observer = new MyObserver(model);
        // we change the last name of the person, observer will get notified
        for(Person person : model.getPersons())
        {
            person.setLastName(person.getLastName() + "1");
        }
        // we change the name of the person, observer will get notified
        for(Person person : model.getPersons())
        {
            person.setFirstName(person.getFirstName() + "1");
        }
    }

}


2. Class MyModel.java

package designpattern.observer;

import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.ArrayList;
import java.util.List;

public class MyModel
{
    public static final String FIRSTNAME = "firstName";
    public static final String LASTNAME = "lastName";

    private List<Person> persons = new ArrayList<Person>();
    private List<PropertyChangeListener> listener= new ArrayList<PropertyChangeListener>();

    public class Person
    {
        private String firstName;
        private String lastName;

        public Person(String firstName, String lastName)
        {
            this.firstName = firstName;
            this.lastName = lastName;
        }

        public String getFirstName()
        {
            return firstName;
        }

        public void setFirstName(String firstName)
        {
            notifyListeners(
                    this,FIRSTNAME,
                    this.firstName,
                    this.firstName = firstName);
        }

        public String getLastName()
        {
            return lastName;
        }

        public void setLastName(String lastName)
        {
            notifyListeners(
                    this,LASTNAME,this.lastName,
                    this.lastName = lastName);
        }

    }

    public List<Person> getPersons()
    {
        return persons;
    }

    public MyModel()
    {
        // just for testing we hard-code the persons here:
        persons.add(new Person("Rahmad", "Nasution"));
        persons.add(new Person("Wandi", "Pratama"));
    }

    private void notifyListeners(Object object, String property, String oldValue, String newValue)
    {
        for(PropertyChangeListener name : listener)
        {
            name.propertyChange(new PropertyChangeEvent(this, property, oldValue, newValue));
        }
    }

    public void addChangeListener(PropertyChangeListener newListener)
    {
        listener.add(newListener);
    }
}

3.Class MyObserver.java

package designpattern.observer;

import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;

public class MyObserver implements PropertyChangeListener
{
     public MyObserver(MyModel model)
    {
        model.addChangeListener(this);
    }
    @Override
    public void propertyChange(PropertyChangeEvent event)
    {
        System.out.println("Changed property : " +
                event.getPropertyName() + " [old -> "
                + event.getOldValue() + "] | [new -> " +
                event.getNewValue() + "]");
    }

}