I've just installed an Xubuntu 16.04 64bit virtual machine in VirtualBox. I used the Eclipse Neon Installer and picked the CDT edition.
Right after I started Eclipse I also tried to install the PyDev from the Marketplace. Right after the dialog window where you select which sub-components you want to install (for example Mylyn integration) I got
Unable to read repository at http://www.pydev.org/updates/content.xml. Unable to make member of class sun.security.ssl.SSLSocketImpl accessible: module java.base does not export sun.security.ssl to unnamed module @7098b8f8
The underlying JDK is OpenJDK 9 (from the official repositories) and I have also tried switching to OpenJDK 8 (using sudo update-alternatives --config java
and selecting the 8th version) with the same poor result. In addition I also have successfully installed PyDev in another machine that is using Xubuntu 16.10 (same architecture).
I was unable to find any hint on what's going on.
EDIT: Updating Eclipse works (I've just updated CDT which for whatever reason was not the latest version).