I wanted the little app I’m making to display a green tick or a red cross depending on whether the user had entered valid credentials. Simple? Yeah. Everything went really well, I extended a JPanel to handle the tick/cross display area (tickCross), got the POST code going, strung together the rest of the GUI elements.
The problem was that tickCross.repaint() wasn’t reliably repainting. about 30% of the time the image wouldn’t be painted. The method was being called, but nothing was happening. I tried Google, re-read the related Sun Java docs and was reminded that: “repaint() does not actually paint. It calls the peer repaint which enqueues a request in some platform-dependent way inside the native GUI for a repaint.” – MindProd. Great. My OS was deciding when I was allowed to draw.