I'm making a 2D game in Java and one of the main issues causing low FPS (on my slow laptop) is having to re-draw complex structures to a Graphics instance, such as dials with markings.
The dial and its markings will never change unless the window is resized, so I thought it would be a good idea to draw to a BufferedImage and just re-draw the image rather than re-drawing the details. The position of the needle obviously changes, so this can just be drawn on top.
I've never heard about this being done to improve the FPS of 2D games so I'm wondering if it's actually good practice to store a cache of images or if there's a better way to solve this sort of problem? Are there any issues associated with this that I haven't considered?
Caching images isn't a bad idea: you can rely on raster rendering to be pretty well optimised on most any platform. In my experience (which is admittedly mostly on mobile devices where 2D graphics are concerned) the Graphics.drawXXX() methods are often considerably slower than Graphics.drawImage().
In my experience the vast majority of 2D games out there make use of sprites (i.e. images) for rendering just about everything. Often that's true even when the graphics look like they are rendered using primitives!
Another useful technique to think about is not redrawing regions at all unless you really need to!
EDIT:
As others have mentioned, the major tradeoff is that you're going to be using more memory. You're also going to have to make sure you free up those images once you no longer need them.