Actually, I don't like a lot of these answers.
Consider mine.
C++ is a language that is compiled (obfuscated) down to Assembly, which is in binary representation, or commands to be run one by one. It is much like batch's goto system. Anything that supports running this code will be able to utilize it, naturally.
Java is similar. Though, Java requires another step in the process. It runs in its own assembly code to assembly, naturally like other languages (mainly script languages). It's super language is C.
There are multiple levels of languages that interact with the system.
C
C++
C#
Java
This list above is the order of closeness of a few languages. C is the closest you can get to the system, but things take too long to make and do in C for a lengthy project such as a video game. That is why people extend things.
Libraries are what makes up a language. If a language has bad libraries, then it has bad functionality. Good libraries are made by me and you, and default libraries included.
C++ and Java are well known for their outstanding libraries. C# tends to focus more on framework, or graphical user interface design, though it is important to show another example of a language.
C++ is a very messy code.
Java is a very clean code.
They both can and do the same thing.
C++ offers memory management.
Java does that automatically.
C++ offers user-garbage collection.
Java offers auto-garbage collection.
Garbage collection is the releasing of unused resources.
C++ is close to C which makes programming games extensive, but not as extensive as C.... no not at all.
I personally find Java fun to make games in.
Overall performance:
C - fastest running
C++ - a tad bit slower than C
Java - 10% slower than C
For preformance, C++ will run better (giving in blind to the programmers coding techniques)
Java is a perfect beginners language.
C++ is better
Java is love, Java is life. (and better packages, personally thought)
You decide really.
One more thing. If you choose C++, you will type double and sometimes triple what you would need to in Java.