From: Tod <todbramble@...>
Date: 2006-09-21T02:35:14+09:00
Subject: Re: Message passing between objects


Paul Lutus wrote:
> Tod wrote:
>
> / ...
>
> > Someone yesterday said you would create a superclass that both of these
> > objects would share and this superclass would handle communication
> > between the objects. I can see how that would work. But is that the
> > only way? Is there no way for ruby objects to communicate directly with
> > one another?
>
> No, in fact, there are any number of ways to do this. The question you
> should be asking is which of the available methods meets your requirements
> most efficiently.
>
> Obviously, using your example of a student registration system, the
> student's identity is the key to the relationship between objects.
> Therefore a parent class containing everything that is known about the
> student should deal with various aspects of the student -- registration,
> arranging for classes, health care, grades, whatever.
> cture is also
> easy for the maintainer to understand and modify.
> In the process of applying for a particular class for example, the object
> responsible for requesting a particular course would pass this request to a
> parent class that coordinates all activities for that particular student,
> and that class on turn would communicate with a class responsible for
> assigning courses university-wide.
>
> The student's data is obviously self-contained, no peer-to-peer transactions
> required. But the communication between the student's data and that
> belonging to the university would be by way of another hierarchy of
> classes, one in which the university's master record-keeping system would
> be the parent of each student record.
>
> My point is true peer-to-peer transactions without a parent class to
> coordinate the activities are rare, and should be avoided if possible. Many
> data relations are naturally hierarchical, and this archite
>
> --
> Paul Lutus
> http://www.arachnoid.com

Thank you so much Paul for taking the time to lay that out for me. I
appreciate it. The reason for the persistent nature of my question
originates from a book I have on Java (I am not a Java programmer but
this book helps me object oriented concepts) in which there is a
sub-heading in a chapter: Message Passing Between Objects (hence my
post title).  In this section it appears (to my hazy mind) that they
are describing a direct object to object interaction. But I may be
wrong.

Here is what it appears to be saying using the student example:

Student s = new Student()
Course c = new Course()

Course c recieves the message: c.register(s)

before Course c can register s it sends a message to Student s, perhaps
s.successfullyCompleted(c2) where c2 is some other course that is
required for the current registration request. Student s replies to
Course c with true. Now Course c can register Student s and confirms
the to whatever originated the request (a GUI perhaps) by returning
true.

To me that looks like two objects communicating directly with one
another. But I am way out of my league here.  The book is "Beginning
Java Objects (2nd Ed) Jacquie Baker (2005 Apress).

But again, thank you for your post above. TOD