The Problem: This problem is based on the chat room example from chapter 10
of Jason Hunter's OReilly Java Servlet Programming.
The example consists of a servlet, a message source class for
holding and sending messages and a message sink class that is an observer of
the message source that returns the message.
This is where my misunderstanding comes in: the servlet contains the line
"MessageSource source = new MessageSource();" which in my understanding
gives the servlet thread its own instance of the MessageSource object called
source. The MessageSource class extends Observable, and if a message is
sent to MessageSource, it calls notifyObservers.
When a new message comes into the servlet to the doGet method (used for
waiting for a new message), the servlet asks for the next message from the
message sink with the line "String returnMsg = new
MessageSink().getNextMessage(source, room);" . So the servlet calls its
own instance of MessageSink. MessageSink is an Observer of the source with
the line "source.addObserver(this);" where the source is the source instance
passed from the servlet.
Now, if my understanding is correct each independent thread of the servlet
has its own instance of the source and its own instance of the MessageSink
that is an observer of its own source object. I want to know how when one
client posts a message, how do the other threads of the servlet (the other
clients) get the message???
The only other thing that I think is relevant is the methods of the
MessageSink class are synchronized, but I still do not see how this would
help given that there are different threads.
Thanks for the help - Scott Carter
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