Hi, I'm trying to do something quite complicated and I'm not sure the best way to make it happen - I'm a Java novice, trying to port some Director code across.

What I have is a fairly complicated Physics engine, where every element is an instance of a PhysObject class. So for example I'll have PhysBall, PhysLineSegment, PhysPolygon etc. What I want to do is to give each instance a method mCollision(tObj) that calculates whether there's a collision between two objects. Now, of course, each object type collides differently, so my plan was to do this

Class PhysObject {
// *****other code****
Collision mCollision(PhysObject tObj) {
// cast to the appropriate subclass and send to the correct function
 if (tObj instanceof PhysBall) {
   return mCollisionWith((PhysBall) tObj)
 } else if (tObj instanceof PhysLineSegment) {
   return mCollisionWith((PhysLineSegment) tObj)
 }
 return new Collision()
}
}

Class PhysBall {
// *****other code****
// now pick up the mcollisionWith function and run it here
Collision mCollisionWith(PhysBall tObj) {
// code here for this collision type
}
Collision mCollision(PhysLineSegment tObj) {
// code here for this collision type
}
}
etc.

This works fine when the hCollisionWith methods are in the PhysObject class. The message is passed to the appropriate version of the method. Unfortunately, when they're in the subclass as above, for some reason they never get called.

I suspect I'm just using the wrong paradigm altogether. Can anyone help put me straight with how this should be done? And I hope I've made the issue clear!

Thanks
Danny

Hi Danny,
thanks for letting us know. It would be great to see some of our final physics-classes once they are finished! Looking forward to it,
Bejoscha