Which open source java project to choose for a beginner?

Question

Java

I know about myself at the intermediate level PHP, Pascal, Asembler, BASH in weak C ++, C #, Python, Java (I am currently learning java)
That is, I understand what OOP is for what it is needed (and so on), there is not enough knowledge syntax in some moments, the desire to try yourself in some easy OS, what can you recommend?
I work as a system administrator, so there should be no problems in the knowledge of networks, databases, etc. (worked with mongoDB) worked with (jira, QC, WebLogic, GlassFish - if it suddenly comes in handy somewhere)
ZY is only interested in Java!

Answer 1

On the one hand, no one bothers you to make pull requests in any of the projects: go to Github search and look for what you are interested in, select Java, in the "With the labels" field write "bug, feature, improvement", in the field "In the state" put "open" and find approximately 604,635 projects.
But on the other hand, judge for yourself, who needs your commits and why? If they are really needed, then your pull request will be accepted, but in general, open-source is not a place for practice.

Answer 2

The best way is to start writing something of your own, and draw the syntax and everything else from the literature, and GitHub. If you want, I can connect to myself, I am writing a web project for practice using hibernate, maven, mysql, JSP, JSTL, Servlets technologies.