A link to what?

Probably noob question. When I updated to 1.16.3 latest, created a new folder and rerun the build programs and create a new java file, all it shows is an empty file. I never experienced something like this modding in 1.12. When I create something in there it gives the package name, the class name, and a ready constructor. 

Hello, I want to have a block, which will take on a texture of a block which player holds in hand if he right clicks on the block placed in the world. So far I got it to change as I like, but it changes all blocks instead of just the single one I clicked on. I suspect, it's because the blocks in game are all just a single object instance and world just has bunch on references to it.   How can I then change the single blockstate (or rather, it's texture, if it helps) ? Do I need to create some kind of registry, which will remember block positions and their blockstates and load the blockstate based on the block position ? Is there something more optimal, because if I have a arraylist of, let's say, 2k block positions and their block states which I need update every so often, I think it's gonna get slow real quick. Or if this IS the best way, then how can I save the registry, so after server restarts, it's gonna remember them?

Do u have a link?  

Same thing I usually do, then. Gotcha. Thanks for this, and sorry I made you sift through that 7GB mess of a log to help.