Hello to everyone on the list. I'm a new Java programmer and have a
question which despite some effort I haven't been able get answered.
As a vehicle to learning Java I've been writing a single program. This is a
crowd simulator. The idea is to create a large number of objects
representing groups of people, have them interact in a 2-d array
(representing a large open space like a park), and display their spatial
locations in a scrollable JLabel. In other words this is animation of a
large number of "sprites" that are moving pretty slowly (like the game Life
running at a slow speed).
My main method invokes a constructor which creates a GUI object, which
itself creates a "scrollableMap" object. This scrollableMap contains the
update() method I use to create a bufferedImage. The main method then
creates a thread, which creates Unit objects (the groups of people) and puts
them in a static array. Finally, the thread enters a while loop which first
goes through the array of units and moves each one, and then sleeps for 50ms
before doing it again.
Here's the problem. My update() method in the scrollableMap creates a
bufferedImage and I can use graphics primitives (e.g. fillRect(...)) to draw
to the buffer and then drawthis image to the scrollableMap. So my buffered
image works fine. What Ican't do is get position data for my units into the
update() method. When I try to do this, e.g. in the update method trying to
invoke methods in the
game thread, my GUI comes out all blank.
All the animation examples I've seen involve some sort of computation to
determine where to draw shapes, and these computations are always very
self-contained so they can sit in an update or paint method. I've looked at
lots of animation demo programs but haven't found any that access data or
methods "beyond themselves." For my simulation the final x,y coordinates
for each sprite will be the product of a large "sim-side" to the program. I
can't do the whole simulation in an update() or paint(). When I try to get
data from outside these methods my GUI goes blank. I've been careful to put
an if-statement in the update() so it doesn't try to access unit data until
the units are created, but it makes no difference.
If there is some fundamental problem with accessing objects and methods
outside an update() from within the update() I would appreciate any advice
on how to get around this. Thank you very much for your time.
Tim Huntington
Boston, MA
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