How do I detect a User interaction?

Question

This question arises more out of curiosity than necessity.
Let's say I wanted to create a Java version of the board game Risk. Let's also say I have an image of the board (a map of the world). How would I be able to tell in which terrritory (country) the user clicked?
Would I have to declare each territory as a seperate object?
-- if so then how would you get the objects lined up nice and neat against each other
Can I somehow include all possible XY coordinates of a territory?
I scanned through the 2dGraphics tutorial but didn't see anything that satisfied this situation exactly.
john

Answer 1

OK,
Solution 1)
So then every territory would need to be a different
color (different least as far as RGB:AAAAAB and
RGB:AAAAAC so that the human eye could not
distinguish), right? But is this good design?Well nations on maps are nomrally very different colors, so it doesn't matter if the human eye can distinguish the difference. I wouldn't say its bad design. In fact I think its pretty good.
Solution #2)
I still don't see how you can specify all possible
coordinates inside a territory. Especially since
almost all territories are not standard geometric
shapes.Solution2 could be considered better design, but much, much harder to maintain and find mistakes. What Solution 2 does is specify each pixel in a boundary. You could make that boundary the whole map or make a seperate one for each nation (which is what I would do). It is just a map of the pixels, therefore you get pixel perfect collision detection. Store the numbers in a text file (rename the extension to .map though; it looks better and you know exactly what the file is for) for best design. The file might look something like:
5, 10
23, 2;
56, 4;
If the file looked like this, then a collision would only be detected or returned if the mouse was clicked at the position:
x=5 y=10
x=23 y=2
x=56 y=4