Design Pattern —— Observer

import java.util.Observable;

public class Product extends Observable
{

    private String name;
    
    private float price;

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
        this.setChanged();
        this.notifyObservers(this.name);
    }

    public float getPrice()
    {
        return price;
    }

    public void setPrice(float price)
    {
        this.price = price;
        this.setChanged();
        this.notifyObservers(this.price);
    }
    
    
}

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

public class PriceObserver implements Observer
{

    private float price = 0.0f;
    
    public void update(Observable o, Object arg)
    {
        if(arg instanceof Float)
        {
            price = ((Float)arg).floatValue();
            
            System.out.println("Product price has changed : " + price);
        }
    }

}


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

public class NameObserver implements Observer
{
    private String name = null;
    
    public void update(Observable o, Object arg)
    {
        if(arg instanceof String)
        {
            name = (String)arg;
            
            System.out.println("Product name has changed : " + name);
        }
    }

}


public class ObserverTest
{

    public static void main(String[] args)
    {
        Product p = new Product();
        p.setName("apple 4");
        p.setPrice(5.52f);
        System.out.println(p.getName());
        System.out.println(p.getPrice());
        
        p.addObserver(new NameObserver());
        p.addObserver(new PriceObserver());
        
        p.setName("apple 5");
        p.setPrice(6.15f);
        
    }

}