CDCMS-TNNLS2020

[Please use this version]

Adding back the required interface class for QStatistics.java.
It will cause "java.lang.ExceptionInInitializerError" when it is missing.
This is not an update to the implementation of CDCMS. This file had been used in the experiments of the published paper. I just forgot to upload it. My apologies.

This version of CDCMS is used in [1].
[1] CHIU, C. W.; MINKU, L. L. . "A Diversity Framework for Dealing with Multiple Types of Concept Drift Based on Clustering in the Model Space", IEEE Transactions on Neural Networks and Learning Systems (IEEE TNNLS), 2020 (accepted).