An aside, depending on what your actual goal is: If you just want to compute a dot product (or similar standard operations) with CUDA via JCuda, you should have a look at JCublas. It has built-in functions for that - for example, the dot product.
(The relevant lines in an otherwise unrelated sample - some other JCublas samples are at jcuda-samples/JCudaSamples/src/main/java/jcuda/jcublas/samples at master · jcuda/jcuda-samples · GitHub )