You wont achieve 'High speeds' with Java in general, the best ones out there are pure optimized assembly. Not the entire miners, but the cryptography parts. Another thing to consider as well is GPU vs CPU. CPU is pretty much useless by now, unless you happen to have like 50k computers. And I have no idea if you can even do GPU with Java. Just searched a bit, and it looks like there are ways to use GPU with Java, but still..
Remember, reinventing the wheel is not necessary.