classIndex() performance on ARF

[Junji Watanabe]

Hi MOA experts,

Cross posting a question I wrote on GitHub.

https://github.com/Waikato/moa/issues/227

I realized that classIndex() takes long time on Adaptive Random Forest, and it can speed up by caching the class index at initialization.

But it slows down Hoeffding Tree...

I put code change and some more details in the GitHub issue.

I would appreciate if you give your insights on it.

Regards,

Junji