Prerequisite (Udemy Course) : Java - Object Oriented Programming [For Absolute Beginners] By Achala Chathuranga Aponso or basic understanding of OOP
At the end of the Course you will understand the basics of Java Threads (Concurrency )g. You can enhance your concurrent programming skills to reach the advanced level.
Once you complete the above course and cover the OOP concepts and Java Threads - Theory , It is recommended to Follow this course