|May 17, 1998. This article is a little bit old, but I've gotten feedback from people who have been helped by it so I'm keeping it online. I guess the biggest news for Java and MVC is that Sun's Swing user interface is based on MVC and has rather good documentation on MVC and other topics.|
In early April 1996 I was interested in developing simulation applets in Java and having heard of the "Model-View-Controller" paradigm I posted to comp.lang.java asking about it. Here are the replies I received:
I don't know where there is any information on it but I had to teach myself. Here is a quick summary of what I can tell you about it: Model - only one. It represents the actual object. View - from 0 - infinity. usually one. It represents a paticular view of the model. Controller - from 0-infinity, again usualy one and that one is usualy associated with the view above. It is VERY easy to get functionality mixed up in this because many times the application is set up to have only one of each. Then later on when you want to have more Views or Controls things start breaking down fast. If your doing it with Java check out the Observer/Observable Objects where the Observable is the model and Observer is the View. It is not everything you need but it helps to do the syncronization of the views with the model. Good Luck, Nolan Toone SunSoft, Inc.
There's some discussion of MVC on pp. 176 et seq. of Brad Cox's 1991 "Object Oriented Programming", 2nd ed., but he doesn't give any references, and I don't know of anything more recent. Let me know if you hear of anything. Michael Carroll Research Libraries Group email@example.com
The classic MVC article is: Krasner and Pope (1988), A cookbook for using the Model-View-Controller user interface paradigm in Smalltalk-80. Journal of Object-Oriented Programming.1(3) Combining the View-Controller as well as the classic structure is discussed in Wolfgang Pree (1994), Design Patterns for Object-Oriented Software Developement, Addison-Wesley.
Paul, You can find reference to this topic in the Gang of Four (GOF) Design Pattern book. In addition, there's a Siemen pattern site which also include coverage on the same topic. It's at http://st-www.cs.uiuc.edu/ftp/pub/patterns/siemens/ Check it out! ********************************************************** Jake P. Doan Motorola SatCom/IRIDIUM Inc. Email address: mailto:firstname.lastname@example.org **********************************************************
The book "Smalltalk - The Language" by Goldberg and Robson explains the critical part of MVC which is dependencies. (The Java equivalients are Observable and Observer) MVC - Model-View-Controller The model is your set of physics classes The view and controller are merged in Java. The basic idea is that you have your views register as dependents of the model. When the model changes it notifies all dependents (e.g. - Those who've registered) and then those objects can then react. In the case of views they can redraw. The dependency notification is through the msg notifyObservers. All objects that are observers need to implment the update mthd b/c this is what the notifyObservers msg will turn around and send to all the registered observers. Note: Dependents can be other objects also. hope this helps, Sam Griffith Jr. Staypufed@aol.com
> Hi, I'm writing some physics simulation applets (I will > probably have them webbable by the end of the week) and I've hit > upon an architecture that somebody said was a lot like something > called the Model-View-Controller paradigm. > > Anyway, I have been looking for some basic introduction to > the MVC paradigm, although I haven't been able to find anything > cogent about it on the web or in print. Can anybody direct me to > a good starting place? Hi Paul, By the date on this email, you've probably received hundreds responses and have gone on to build your applet, but for what it's worth...Model=your data object, View=you applets, Controller=java.util.Observable. Subclass your data classes from java.util.Observable. For each applet that is interested in displaying the data, build the class and have it 'implements Observer' meaning it implements the update() function call and call Observable.addObserver. Whenever your data changes, possibly from a write event from your simulator or interaction from the user, you can notify your observers in several ways: 1)Seed your data object to call Observable.notifyObjservers() at key points in the code, 2) seed your code with Observable.setChanged() and have your observers poll to find out if the data Observable.hasChanged(), or 3) build a 'wrapper' subclass of your object that notifies the registered applets when something interesting (to them) has happened. Once the observer applets receive the event, they can query your data object with non-changing calls. There are all sorts of ways you can extend java's MVC, by filtering events, registering for specific interface calls, registering for specific data values, etc. but they involve subclassing the controller, ie. Obervable. Greg