To create detailed documentation, you need to build a diagram of the processes occurring in the Java code. Yellow in UML notation, but it can be in any other. What tool for this use?
On the Internet there are a lot of links to software and events that happened more than 10 years ago, when there was an extensive HYIP around the subject of UML. It would be nice to have some kind of modern tool that has gone through all these decades and just works.
The corresponding plug-ins for IntelliJ IDEA, for example, are rotten completely, with release dates for 2007. As far as I understand, modern semi-dynamic Java code can no longer be analyzed without knowledge of the work of the frameworks, which only the IDE can usually do. That is, it is assumed that this software should be a plug-in for IntelliJ IDEA, at the very least Eclipse, or be standalone - but still fantastically clever, or simply use some methods of runtime analysis.
It is important to emphasize: the class diagramming tool is not needed at all (for this you can simply use the Code Iris plug-in for IntelliJ IDEA), you need a parsing-modeling tool for the effects of the imperative Java code itself.