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public class Table {
 
    ...
 
    /**
     * Sets the Kitchen that should be notified when items are added.
     * Note that this method may be called several times with different Kitchen objects.
     * @param kitchen
     */
    public void setKitchen(Kitchen kitchen) {
        ... what should be done here? ...
    }
 
    ...
}
 
/**
 * Interface for classes that want to know when Courses have been produced by a Kitchen.
 */
public interface KitchenListener {
    public void courseReady(Table table, Course course);
}
 
/**
 * Manages a queue of courses to produce, based on what is requested by Tables.
 */
public class Kitchen {
 
    // for each Table that has requested Courses,
    // there is a Collection of the thoseCourses that are yet to be made
    private Map<Table, Collection<Course>> courseQueue = new HashMap<Table, Collection<Course>>();
    
    /**
     * Enqueues a Course in the production queue, that is part of the provided Table.
     * @param table
     * @param course
     */
    private void produceCourse(Table table, Course course) {
        Collection<Course> courses = courseQueue.get(table);
        ... what should be done the first time a Table requests a Course? ...
        courses.add(course);
        courseQueue.put(table, courses);
    }
 
    /**
     * Internal methods that must be called when a Course of a Table has been produced.
     * Notifies registered listeners about the event.
     * @param table
     * @param course
     */
    private void courseProduced(Table table, Course course) {
        Collection<Course> courses = courseQueue.get(table);
        courses.remove(course);
        ... what should be done here, to support observers? ...
    }
 
    /**
     * Should be called when a MenuItem is added to a Table,
     * so the corresponding Courses can be produced.
     * @param table
     * @param item
     */
    public void menuItemAdded(Table table, MenuItem item) {
        ... handle cases when item is a Course or a Meal ...
    }
 
    //
    
    ... fields and methods for supporting observers ...
}

Vi trenger et felt for Kitchen og en setter (oppgitt i koden). Vi må også si fra til Kitchen-objektet om nye bestillinger i addItem-metoden.

private Kitchen kitchen;


// setter
public void setKitchen(Kitchen kitchen) {
	... her kommer det mere siden ...
	this.kitchen = kitchen;
	... her kommer det mere siden ...
}

// må si fra til kjøkkenet (hvis satt) når noe bestilles
public void addItem(MenuItem item) {
	this.items.add(item);
	if (kitchen != null) {
		kitchen.menuItemAdded(this, item);
	}
}

 Dette er standard bruk av observatør-observert-teknikken, altså må en ha felt med liste av lyttere, metoder for å legge til og fjerne lyttere og helst en hjelpemetode for å varsle dem.

public class Kitchen {
 
	...
 
	private Collection<KitchenListener> kitchenListeners = new ArrayList<KitchenListener>();

	public void addKitchenListener(KitchenListener listener) {
		kitchenListeners.add(listener);
	}

	public void removeKitchenListener(KitchenListener listener) {
		kitchenListeners.remove(listener);
	}

	private void fireCourseReady(Table table, Course course) {
		for (KitchenListener listener : kitchenListeners) {
			listener.courseReady(table, course);
		}
	}
}

Table må implementere lyttergrensesnittet og dermed også varslingsmetoden(e), og en må huske å registrere den når Kitchen-objektet settes. Dette kompliserer setteren, siden den både må avregistrere seg fra det forrige Kitchen-objektet og registrere seg på det nye.

public class Table implements KitchenListener {
 
	...
 
	public void setKitchen(Kitchen kitchen) {
		if (this.kitchen != null) {
			this.kitchen.removeKitchenListener(this);
		}
		this.kitchen = kitchen;
		if (this.kitchen != null) {
			this.kitchen.addKitchenListener(this);
		}		
	}
 
	@Override
	public void courseReady(Table table, Course course) {
		// reaksjon på varslingen
	}
}