Just open JavaCrashCourse.md file in any markdown editor (github works as well). There is also helper functionality of quickly running code snippets implemented in runSnippetFromKeyboardShortcut directory. To use it you have to:

• download that directory
• have JDK installed with java and javac added to PATH
• on Windows download autohotkey from https://www.autohotkey.com/
• on other OS write script which triggers Python codes inside directory with e. g. keyboard shortcut

Autohotkey makes it possible to compile and run java:

• without arguments with ctrl+shift+j shortcut
• with arguments with ctrl+shift+i shortcut
  To use it select or copy code snippet and then press keyboard shortcut. You can change shortcuts by editing .ahk text files.

Issues:
It shouldn't be too troublesome for simple snippets, but:
Python creates separate files for every public class, interface or record, but separates them by beginnings of their declaration, which makes all imports under first public class/interface/record don't work for classes below. To completely avoid it use only one public class/interface/record or improve Python codes:)