Project setup

[RedemptionC]

I'm confused about the setup. in Readme, it states that we should use JDK 8, I installed JDK 8 (Corretto), but in the repo, it clearly used some features introduced in more recent Java versions, such as Var and record

Also, there seems to be a mismatch between package name and project structure:
for example the file CompletableUtilities.java is in .../OnJava8-Examples/concurrent/CompletableUtilities.java, but the package name declared in it is onjava, the compiler complains: Package name 'onjava' does not correspond to the file path

I tried to use a workaround adding the project's root directory into the dependency in Jetbrains Idea's IDE setting (Project structure -> modules -> dependencies -> add JAR or directories)
It seemed to solve the mismatch issue, but then there're other weird problems, such as on @OverRide: Method does not override method from its superclass

at last, in the readme, when referring to the right Java version, it points to Oracle's JDK 8, what's wrong with OpenJDK?
@BruceEckel

[RedemptionC]

Also, when trying to build this project ( in Idea), it shows error like this:
A problem occurred evaluating root project 'OnJava8-Examples'.

Failed to apply plugin 'com.mindviewinc.tagging'.
Cannot add task 'Applicator' as a task with that name already exists.