event notification in Java

In java, I f开发者_C百科eed very confused on observer pattern or JMS. I want to use the event notification like below. Let us forget about those JMS or Observer, do you think it is possible or doable ? if yes, how to complete it ?

newSalesOrder = new SalesOrder();
newSalesOrder.notified("new SalesOrder order ID="+orderId);

EventRegister.bindEvent(SalesOrder.class, Delivery.class);
EventRegister.bindEvent(SalesOrder.class, Warehouse.class);

////////////
Delivery delivery = new Delivery();
delivery.listerning(new Event(source){
  if(source == SalesOrder.class){

  }  
});

//////////
Warehouse warehouse = new Warehouse();
warehouse.listerning(new Event(source){
  if(source == SalesOrder.class){

  }  
});

///////////
EventRegister{
    static bindEvent(Class source, Class destination){
      //???
    }
}

You need to register (bind) objects not classes. You can keep registration list static at EventRegister but I think it's better to keep them as instance at SalesOrder. So it would be:

import java.util.ArrayList;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        SalesOrder mySalesOrder = new SalesOrder();

        Warehouse myWarehouse = new Warehouse();
        mySalesOrder.addListener(myWarehouse);

        Delivery myDelivery = new Delivery();
        mySalesOrder.addListener(myDelivery);

        Event myEvent = new Event();
        // Now 'myDelivery' and 'myWarehouse' objects will receive 'myEvent'
        // object on their 'onEvent(Event event)' method
        System.out.println("Event to be published: " + myEvent);
        mySalesOrder.publishEvent(myEvent);
    }
}

interface Listener {
    public void onEvent(Event event);
}

class Event {
    // Add reqired detail here!
}

class SalesOrder {
    private List<Listener> listeners = new ArrayList<Listener>();

    public void addListener(Listener listener) {
        listeners.add(listener);
    }

    public void removeListener(Listener listener) {
        listeners.remove(listener);
    }

    // Use proper access modifier
    public void publishEvent(Event event) {
        System.out.println(this + " is goint to publish " + event
                + " to " + listeners + " listeners.");
        for (Listener listener : listeners) {
            listener.onEvent(event);
        }
    }

    // ...
}

class Warehouse implements Listener {
    public void onEvent(Event event) {
        // Do something when event received
        System.out.println(event + " received at " + this);
    }
    // ...
}

class Delivery implements Listener {
    public void onEvent(Event event) {
        // Do something when event received
        System.out.println(event + " received at " + this);
    }
    // ...
}

If you run it it will print something like:

Event to be published: Event@190d11

SalesOrder@a90653 is goint to publish Event@190d11 to [Warehouse@de6ced, Delivery@c17164] listeners.

Event@190d11 received at Warehouse@de6ced

Event@190d11 received at Delivery@c17164

This is a trivial sample, in real life use cases you may consider using a thread-safe implementation and refactoring registration out of SalesOrder using composition or inheritance.