Difference between rosjava_core vs. rosjava vs. ros_jni

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@coolbeans rosjava in general is a reimplementation of ROS architecture in Java. As you can see in the Github organization, it has many components ( https://github.com/rosjava ). All of them can be referred generically as rosjava: you have the tools to build rosjava packages, which are a bit different from standard ROS packages and need some other tools to build; you also have message generators and so on...

Rosjava core is basically where all the implementation is. There you will find nodes, topics, services, etc. Rosjava is supported; perhaps it's not as well known as the standard ROS implementations, but it does it's job. With roscpp you will probably have more packages available out of the box. If you are comfortable using Java, I suggest you to try it, specially if you don't require a particular package that is already written in Cpp or Python.

Check out this post for more info https://discourse.ros.org/t/is-rosjav... . And also the wiki entry: http://wiki.ros.org/rosjava .