Oh my goodness...I'm sorry to say this but the people who have replied to your question are either misinformed or just fooling around because please people, just answer his question....
I have learned BOTH languages and have programmed games and here is the scoop:
1. C++ is the defacto-standard in game development such as big titles like Unreal Tournament, Crysis, and many, many more.
2. Java too is used for games but its use is mostly for things like online games (and even then Flash has taken over this department almost entirely -- e.g., check Yahoo Games..they use to be Java-based, not anymore!), and for mobile phone games (Java-based things such as games are mostly on mobile devices these days -- its called J2ME).
3. Java is mostly used today for application and gaming development on mobile devices such as smartphones. Although Java is used for desktop development it is quite small and religated to potential developments that run on non-PC platforms. That is primarily the only real reason anyone would use Java to make a desktop app today. The primary flaw with Java is that it is too darn slllloooowwww when it runs on computers...However, with the Adobe AIR/Flex (Flash-based) Java will have lost its entire usefulness on the desktop platform and will only be useful on mobile devices, that is, until Flash invades that realm too. Flash-based apps/games are very fast running and quite good.
4. C++ and Java in terms of language syntax are very, very similar. Although people here say C++ is for beginners it is a misunderstanding because Java bases itself on C++ and tried to make things "easier" for beginners...so Java is actually more for beginners than C++ is. However, i would always recommend newbies learn C before tackling C++ or Java because of a thing called OOP (Object Oriented Programming) which they are known for. I think its important for newbies to understand memory management and such before moving onto Java which essentially pampers the programmer and you never see any of that.
5. C++ is used for high-end game development because of its POWER and speed...Java could NEVER do this! But for small, simplier tasks Java most certainly is up to the task. C++ gives you a lot of finesse in what you can do that Java can only dream of...But there is a trade-off....C++ is much more difficult to program under (e.g., you handle memory allocation/deallocation) but the results end up being more superior to Java...especially in terms of performance....
6. Java is more for rapid-application development and C++ is for more power control. You get more freedom to explore things in C++ than you could with Java.
If you learn C++ then learning Java is not that hard...Seriously, for me i had learned C++ and when i first got to see Java in University i literally picked it up in 1 day....I'm serious! Java just scales back on C++ and makes things much simpiler (but that isn't always a good thing btw). However, the way Java implements Object-Orientedness is much more clearer and beautiful in it than C++, even though C++'s object-orientedness is much more powerful.
I hope that helps you...If you would like more details feel free to email me...it may take me a bit to respond...i tend to forget to check my email at times