Yes, there are similarities between Java and C#/C++.
C / C++ is a very good language to know, it is the basis of most if not all programs, including other programming languages! If you know that then you are starting to master computer programming.
However, in my experience, C / C++ is the hardest and longest language to learn so make sure you have to commitment to see it through to the level you need / want it!
Hope that helps
.