The goal of this lab is to experiment with a biological simulator, and especially how polymorphism is useful in its design.
As in previous assignments, move into your cs235
directory.
Then clone the repository for this lab and move into the new lab11
directory.
hg clone /cslab/class/csci235/lab11 cd lab11
If you do ls -F
, you'll see an
item simulation
, which
is a directory containing the source code for the
simulation
package, which contains
the grid and windows.
You will not need modify any of this, but you may look
at it if you're curious.
You will be working with various implementations of the
Agent
interface. In addition to what is in that interface,
you need to know a few public methods on the SimulationGrid
class:
boolean isOccupied(int xPos, int yPos)
boolean isOpen(int xPos, int yPos)
Agent getAgentAt(int xPos, int yPos)
void setAgentAt(int xPos, int yPos, Agent a)
Conveniently, the first three of these will do the right thing when you
pass them a position that is outside the grid: both
isOccupied()
and isOpen()
return false, and
getAgentAt()
returns null
. You must, however,
be sure that your xPos, yPos
is in-bounds when you call
setAgentAt()
.
The first thing you should do is glance over the code to
familiarize yourself with it.
This version of the simulator is similar to what you saw in class for the
Life game. In the Life version, every cell in the
grid was occupied by an agent; every agent stayed in the cell in which
it was created; and each step of the simulation
first invoked plan()
for all of the agents, then
step()
, so that all of the agents acted
simultaneously. This version changes all of those: some cells are
unoccupied (so that getAgentAt()
returns
null
), some of the species move from cell to cell, and
each step of the simulation calls a single act()
once for
each agent. The agents therefore move one after another, with each
getting one chance to act in each round.
Compile PredPrey.java
and the species files.
(Note: You will get a warning message about "unchecked or unsafe operations"
when you compile any of your species. You may ignore that.)
Now run the simulation.
You can select between a small view or big view,
by using the -small
and -big
flags, as in
java PredPrey -big &
The big view gets you a world that is 180x120 cells; the small view's world is 60x30.
Try running the simulation with various initial populations. If you observe that either foxes or rabbits have a particular advantage (say, foxes always eat all the rabbits before the rabbits eat all the clover, or if clover always becomes extinct), then you can adjust the reproductive threshold, speed, or visual acuity of one or more species to try to put them on more equal footing. Try to find an initial setup where you cannot predict the outcome--- where the outcome partially depends on the random placement and movement on the agents; for example, you might find that with 100 clover, 20 rabbits, and 5 foxes, sometimes the rabbits will become extinct, and other times the clover becomes extinct.
Take notes regarding your observations about the patterns of behavior. If you notice any peculiarities, can you explain why they happen? Can you think of a way to eliminate any oddities?
Now you and your partner should think about what major changes you
would like to make to the system to make it more interesting. (And don't
forget that you can use hg commit
to save the state and
hg revert
to back out of unhappy experiments.)
Some obvious directions include the following:
Once you compile a new subclass of Agent
in your
directory, that class will automatically show up in the initial-population
dialogue when the simulator starts.
The Java documentation includes
a list
of pre-defined color names that are available after
importing java.awt.color
.
Some ideas that students have come up with in the past:
When you have an idea, talk to me first so I can help you refine it and point you in the right direction on how to implement it.
As you try out your modified simulation, look for patterns of behavior. What parts seem to be realistic in modeling the real world? Can you make the system stable (no species becoming extinct, at least for a long time), or can you at least find a starting configuration where the results are unpredictable?
Along with the code you wrote or modified, for this lab you should turn in a short report (a few paragraphs long). Talk about what you initially observed in the simulation before you modified it; what you wanted to change to make the simulation more realistic or interesting; what changes you made (including an explanation of the implementation and references to what part of the code you modified); and what you observed when running your new version of the simulation. You may write the report in a text file.
Turn in a hardcopy of your report.
In addition, turn in the .java
source files for your
species with a command like
/cslab/class/csci235/bin/handin lab11 Clover.java Rabbit.java Fox.java
Be sure to include any new species that you have added.