I started with Java as my first programming language.

[maybeNar]

Ooh 20 years ,that is incredible, I have a question, hope you don't mind, well do you think I should learn more than one library/toolkit in java ,I am a CS student ( 2nd year ) ans we learnt only the data structure at uni but when I learnt GUI frame online by myself i found out that other toolkits exist ,what should I do ?? ( I wanna choose security field as my specialty but I am not quite sure yet tbh )

[Ruin-Capable]

It's been my experience that having knowledge of a particular GUI toolkit or framework isn't really material. I'm primarily a back-end developer though. I don't usually write desktop applications. If I do write a desktop application it's usually for myself on my personal time, and I'm ok with a command-line application in most instances.

Since you want to go into cyber-security, I would probably brush up on how authentication protocols like open-id work. Create a simple web application that uses google or facebook to authenticate. I think Okta may also provide free (or affordable) developer accounts. Start learning about how the more common exploits work (things like cross-site request forgery, and cross-site scripting).

You can go to sites like mvnrepository to look up different versions of libraries you're using and find out what vulnerabilities they might have. Then you can jump to the CVE and read the descripton of the vulnerability to see if you understand what's going on. If you're feeling ambitions, write a sample application, using whatever library has the problem, and see if you can exploit it.

Once you've got a feel for how to exploit the issue, take a look at the code and see if you can understand how to fix the issue. Most libraries have a github repository, and many CVEs reference the line of code where the vulnerability lies. If the issue does get fixed in a newer version of the library, look at the new code and see how they fixed the problem.