Please suggest how to start on ML/AI using raspberry pi with java.
And tools, reference. most of them are available in python. however i am interested in using java libraries.
A popular Pi project is to attach a camera to a Pi and set it up for object recognition. That is, a smart "doorbell cam". A long term project for me is, in fact, detecting when the mail truck goes by.
You're correct in that the bulk of AI on the Pi is Python-based, though.
There are a number of neat little inexpensive gadgets these days that can offload some of the AI work. Devices that use SPI or I2C interfaces can generally be hooked up to the PI's GPI ports with little or no extra interface circuitry and in some cases, you'll even find support software for them in the standard Pi OS package library,
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.