A. Ganse, APL-UW, 1999-2009
MiniSim is a Java2 program thrown together as a test demonstration of a networked Dept of Defense simulation client. The simulation networking component itself was part of a software framework that can't be shared with the public, but a key concept was that the client is separable from the simulator so that this part can be shared publicly. I suppose that really turns this program into more of a demonstration of Java2 GUI implementation, but maybe that's useful to someone too. (Like myself in six months after I've forgotten all about how I coded this thing.) A screenshot of the application is in the file screenshot.png.
The other thing that MiniSim may be useful in demonstrating is for creating a single piece of Java2 code that can run as both an independent on-screen application and as an applet situated on a webpage. So you can run MiniSim either by entering at the command-line:
> java -jar MiniSimDemo.jar
or by bringing up the webpage MiniSim.html in a window of a web browser that supports Java2 (that webpage in turn calls up MiniSimDemo.jar). Any modern browser should support that, but just in case, you can always get a Java plug-in at http://www.java.com. Either way the Java applet/application should run right from the provided jar file. But you can recreate it via the makefile (I know, I know, but let's not start another "make" vs "ant" argument here) as follows:
> make
This compiles the *.java code into *.class files and puts the class files into MiniSimDemo.jar, and also creates the JavaDoc directory documenting the Java structure of the code. To view the JavaDoc output point your web browser to the file doc/javadoc/index.html. You can also recreate the MiniSim.src.jar file via:
> make srcjar
And to remove all the extraneous files created during the above:
> make clean
MiniSim essentially consists of two halves: the graphical user interface (GUI) that we see on the screen, and the simulator interface that keeps track of the numerical values for the various objects being simulated and communicates these values back and forth with other simulators. A UML class diagram for the program is provided in the file classDiagram.gif (and I must credit ArgoUML for its handy open source UML diagramming ability). The classes related to the GUIFrame are on the left, and the classes associated with the simulation interface SimInterface are on the right. They're both instantiated from the main MiniSim class. The GUIFrame is updated and redrawn every quarter of a second or so (or however often one likes) by the AnimTimer. Before redrawing its time slider and little submarines on its map display, GUIFrame asks the latest values for those things from the SimInterface, which runs as a separate thread and updates itself at some different rate by the SimTimer (generally faster than the GUI updates). The GUIFrame also accepts some input, like mouse-clicks for new sonobuoy drops, which it passes on to the SimInterface.
The SimInterface is the key to a networked simulation implementation. MiniSim gets from its SimInterface the time and an up-to-date list of the positions, speeds, and so on from each NavalObject (like submarines and sonobuoys) participating in the simulation. The NavalObjects might be local in the same Java program instance on the same computer, or they might be running on some remote computer. The Submarine and Sonobuoy objects specified locally within this example code are very rudimentary in terms of their motion and sensing abilities, but the SimInterface could alternately take the Submarine and Sonobuoy information from more complicated "real" simulators running outside of MiniSim, providing their information either via simple network sockets or a more involved simulation framework, to the SimInterface. My original intent with this public demo version of the code was to create a simple socket framework in the SimInterface so that two MiniSim instances on the same LAN could automatically find each other via sockets and send the sub and sonobuoy info to each other in a "Battleship" game-like demonstration. Each "player" would not see the other's sub but each would deposit sonobuoys into the field that ping when sensing the other's sub. Alas I never got to that part. Still, the thing operates on its own and lets you deposit sonobuoys which report sensing the sub while it drives around. So again it's a GUI/simulation demonstration rather than a fun game to play with (or you'd have to be REALLY bored).
Andy Ganse
Latest update 16sep2009: With more recent releases of Java, note that when I compile the Java code now with Java1.5 on OSX I see the following warning: "Note: ./SimInterface.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details." The applet/application still appears to run fine as both applet and application, but before relying on it for anything else you may want to go figure out the "unchecked" or "unsafe" part of the code to stay current. A super quick initial Googling seems to imply this might relate to one of the Enumeration calls and might be new with Java1.5, but that was a very quick look and I'm honestly not sure...