PizzaObserver.java

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

class Margherita extends Observable {
    private boolean isOutOfDate;
    
    Margherita() {
        this.isOutOfDate = false;
    }
    
    public void setOutOfDate(boolean outOfDate) {
        this.isOutOfDate = outOfDate;
        
        // Tell Java : I have changed
        this.setChanged();
        
        // Tell Java : Notify my observer(s)
        this.notifyObservers("Pizza out of date");
    }
}

class Chef implements Observer {
    Chef() {
        System.out.println("Hello, I'm Mario from JavaPizza");    
    }
    
    // Called when a Chef's Observable has changed
    public void update(Observable pizza, Object details) {
       System.out.println("Mamamia! Something happened");
       System.out.println("Details: "+details);
    }
}


public class PizzaBusiness {
    public static void main(String[] args) {
        // Mario is the Chef running the Pizza Business
        Chef mario = new Chef();
        
        // Margherita is one of the pizzas Mario sells
        Margherita pizza = new Margherita();
        
        // Mario will always check that his pizza isn't out of date
        // Mario will observe it
        pizza.addObserver(mario);
        
        // Imagine a logic based on time
        // .....
        pizza.setOutOfDate(true);
    }
}