public final class CustomerArrivedEvent extends Event {
    private final int customerNumber;

    public CustomerArrivedEvent(int customerNumber) {
        super();
        this.customerNumber = customerNumber;
    }
}

public class Order {
    public Order() {
        //create order
        //...
        EventPublisher.publish(new OrderPlacedEvent());
    }
}

public class Order {

    private List<Event> events;

    public Order() {
        //create order
        //...
        events.add(new OrderPlacedEvent());
    }

    public List<Event> getEvents() {
        return events;
    }

    public void clearEvents() {
        events.clear();

    }
} 

@Test
public void shouldPublishEventWhenCreateOrder() {
    Order order = new Order();
    List<Event> events = order.getEvents();
    assertEquals(1, events.size());
    Event event = events.get(0);
    assertTrue(event instanceof OrderPlacedEvent);
} 

public class OrderRepository {
    private EventPublisher eventPublisher;

    public void save(Order order) {
        //save the order
        //...
        List<Event> events = order.getEvents();
        events.forEach(event -> eventPublisher.publish(event));
        order.clearEvents();
    }
}