Javadoc is a tool that comes with the JDK, which you can use to generate documentation which looks like the standard
Java API documentation.
It works like this: you put specially formatted comments above your classes, methods, interfaces etc., then run the Javadoc tool on your source code, and it then produces a directory containing HTML files.
See the
documentation about Javadoc.
Javadoc comments start with /** and end with */. Here's a simple example: