OpenCL4Java is a thin Java wrapper around OpenCL's C API.
It uses JNA as its interop layer library, which means it works on all of the (many) JNA-supported platforms (see http://jna.dev.java.net/).
It is autogenerated by JNAerator (http://jnaerator.googlecode.com/), so updates to newer OpenCL specs are a matter of seconds.
Note that OpenCL4Java is used by JavaCL, an Object-Oriented API that presents OpenCL in a much more practical, powerful and idiomatic way to Java.
For more info, please visit http://code.google.com/p/nativelibs4java/wiki/OpenCL.