Bootstrap ($JAVA_HOME/jre/lib/rt.jar)
Extension ($JAVA_HOME/jre/lib/ext/*.jar)
System    ($CLASSPAT)

User-based classloaders inherit the System-one

2024
https://habr.com/ru/companies/isp_ras/articles/788618/
2019
https://medium.com/javarevisited/java-virtual-machine-jvm-internals-part-2-class-file-format-7752e5f7dbbe
    https://habr.com/ru/company/otus/blog/478584/
https://medium.com/javarevisited/java-virtual-machine-internals-class-loader-eea706eb37d9
    https://habr.com/ru/company/otus/blog/468193/
https://www.baeldung.com/java-classloaders