In preparing for the forthcoming book in Processing and OpenCV, I have tried to build the Java binding in OpenCV 3.2. It worked easily for the basic components. Nevertheless, when I included the contribution module – optflow, it failed. After a number of attempts in various platforms, I found it was due to the gen_java.py script in folder opencv-3.2.0/modules/java/generator. I tried to add back the import details for the class DenseOpticalFlow. It worked again. Here is what I patch in the gen_java.py script.
For those who do not want to build it yourselves, you can download a pre-built version of the OpenCV 3.2 Java library. You can use it with Processing immediately. I have tested it with the current Processing at 3.3. It contains the following files for various platforms in 64 bit:
Enjoy and happy coding.