ClodHopper is a Java library for high-performance clustering of numerical data. It contains clustering implementations such as K-Means, K-Means++, X-Means, G-Means, Fuzzy C-Means, Jarvis-Patrick, and various forms of hierarchical clustering. ClodHopper's clustering implementations take advantage of the host system's concurrent processing ability to speed clustering. The data structures are also very lean to conserve memory usage. ClodHopper is very extensible. If you are developing a new clustering algorithm, you may save yourself an enormous amount of work by extending a ClodHopper base class.
jmemcached is a fast network available cache daemon. It is protocol-compatible with memcached, but written in Java and suitable for applications with portability concerns, where Java is the preferred solution, or for using the memcached protocol in embedded applications with alternate storage engines. Existing clients for memcache work unmodified. It can run as a standalone daemon or be embedded inside an existing Java application.