Two java files. Getting IllegalAccessError when running class with main method trying to access a method from the other file

Question

Learning Java. I have two files, each containing one java class. When I run the file with the main method, I get the following error:

Exception in threa

Answer 1

Actual Issue

I got this exact same error* doing something very silly:

I tried to run the file as java {main-class}.java. That simple!

Instead, be sure to run it simply as java {main-class}.

*Specifically, the error format I had, like yours:

Exception in thread "main" java.lang.IllegalAccessError: failed to access class {pack.other-class} from class {pack.main-class} ({pack.other-class} is in unnamed module of loader 'app'; {pack.main-class} is in unnamed module of loader com.sun.tools.javac.launcher.Main$MemoryClassLoader @29f69090)

  at {pack.main-class}.{who-cares-where}
  at {pack.main-class}.{who-cares-why}
             . . .

Extra Advice

You can get a similarly annoying error on the same issue, namely inability to access packages in the same directory, if you only compile your {main-class}.

So instead of javac {directory}/{main-class}.java

Be sure to compile all of them at the same time, so there's no issue in cross-referencing:
  javac {directory}/*.java

OP Specific

This would just be a silly command-line mistake. If it's occurring in IntelliJ as well, as you say, this isn't your issue. However, I hope it's at least helpful to the others who come across your question with this error!