Parag,
At the moment, we do not have the conventional way of Java docs for UM Java API[u]. You can still refer the class and methods to access them in your code, Also as mentioned, look the java code samples which might help you to re-use some piece of code.
You can raise a request to SAG, to update their UM Java API docs.
#webMethods#Universal-Messaging-Broker#Integration-Server-and-ESB