Using Numix as the theme on Xubuntu 16.04 LTS, we find that Eclipse IDE toolbars, fonts, menus have excessive spaces between them. They look too big and take away screen real estate forcing you to scroll more.
If you change the
Settings -> Appearance to Greybird and
Settings -> Window Manager to Daloa or something else, you will find that the Eclipse IDE tool bars, fonts, menus are back to normal. You can do this if you can live without the Numix theme.
If you still want to use the Numix theme, then see the workaround at https://gist.github.com/andrioli/3825078#file-gtkrc-eclipse