getClass().getResource() always returning null

You need to check that, however you're building, the image file gets copied over to wherever the class files are compiled to. I.e. if your class is com.foo.MyImageLoader and located at <build dir>/com/foo/MyImageLoader.class, then the image should be at <build dir>/resources/01.png for you to be able to load it like that.

I had to clean the build and then rebuild. Works now.