On Mar 13, 2006, at 3:09 PM, Geir Magnusson Jr wrote:
public interface Monitor {
public void monitorEvent(
<some type> eventType,
<another type> eventData );
}
and I hadn't worked out what <some type> or <another type> was. I
figured that you could then add events w/o worrying about clients,
because a client would simply ignore any type it didn't know how to
handle. One less thing to worry about when upgrading the kernel.
I thought of a few approaches, such as <some type> == int and
<another type> depends on the approach you wanted to take. Map
(for named values), Object[] for a known set of values, or even
some base MonitorData which the client could cast to the
appropriate type if it understood the eventType, or if not, call
toString() or something to get *something* to put in the log to
inform a human that something new was coming out...
I considered this style, but it occurred to me that everyone would
write a listener containing a switch, which seems like busy work to
me. Also, this style event assumes that every event fires the same
data.
I think the best way to deal with this is to encourage every one to
extend the NullMonitor which provides no-op implementations of every
method. That way they always pickup new methods.
As I wrote before, the biggest issue with using a Monitor is the work
involved in designing the monitor interfaces. If they are to
specific, you don't have upgrade problems, and if they are too
generic they are difficult to use. You also need to choose how many
monitors you need and the granularity. All of these are very tricky
issues to get right the first time you write a system. In XBean, I
had an advantage as it was the 4th kernel system I've written, so I
already knew the events users would want to monitor.
-dain
