“Cannot subclass the final class” error, but the class is not final [closed]

You are extending java.lang.Character (which does not need an import, as it comes from java.lang).

Insert import characters.Character into your Player code.

Reference: using package members:

For convenience, the Java compiler automatically imports two entire packages for each source file: (1) the java.lang package and (2) the current package (the package for the current file).