Can java do everything whichever matlab does? what can java do?

[independent]

hi,

I am entry level (newly started) at java programming, can someone explain whether java can do everything whichever matlab does? (i.e. is it free?)
otherwise, do we have to buy a license of matlab?

and can someone also explain what can be done by java programming by giving specific samples of products/applications generated by java programmers.

further consideration: I am willing to be specialised in cyber security , so will I benefit by this knowledge if I learn it well.

Thanks.