You need to install a JDK (same java version as you are using) and add it to the PATH environment variable, if the installer doesn't do it automatically.
If you dont know how to do this, there are plenty of guides/tutorials on Google.
"DeferredRegister<>" should look like "DeferredRegister<>" but because it is "depricated"(whatever that means) it wont work.
It causes no problems when running the mod, but it doesn't let me build it.
*btw I'm using IntelliJ