Ok, I'm not really using a graphic engine as such, so I'm guessing showing more of the map would be better.
I've decided that, I could have two variables like
int tilewidth, tileheight;
And then when I render my tiles I can do:
g.drawImage(img, x*tilewidth, y*tileheight, tilewidth, tileheight);
Then if the user scrolls the mouse wheel, then I can have tilewidth and tileheight to change or I could simply have a little icon for zooming in or out. I would need to restrict how far to zoom in, otherwise I could end up with a single tile taking up 640x400 or whatever resolution I finally end up with.
If the user resizes the window, will it automatically render more of my map?