I think you need to make some modifications in your “eclipse.ini” file by adding the below line after -vmargs line:
--add-modules=java.se.ee
This will add all the missing classes in the Java 9 module.
But, if you use Eclipse Oxygen (4.7.1) or more, I think you won’t face this issue any more as it comes with full support for Java 9.
Hope this helps!!