java.lang.RuntimeException: Uncompilable source code - what can cause this?

Question

This error is just bizarre, my code compiles fine, I can see there are no problems with it, yet this error has just popped up. I have tried re-starting NetBeans and there is

Answer 1

change the package of classes, your files are probably in the wrong package, happened to me when I copied the code from a friend, it was the default package and mine was another, hence the netbeans could not compile because of it.