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

If you are using Netbeans, try to hit the Clean and Build button, let it do the thing and try again. Worked for me!