This is similar to the question How to build a Google-chrome tabs and menubar interface in Java Swing? (I want to accomplish the same), but more to the point: How do I put components in front and behind the tabs in a JTabbedPane?
I've already come up with the buttons-idea myself, but I'd rather have a JTabbedPane, since that is really what it is, but decorated with a button or icons on the sides.
I've seen that the laf-widget project from Kirill does something like it (the magnifying-glass icon to the left of the tabs) for several LaFs. However, I must admit that I'm not yet well enough versed to understand how he does it - and also it seems like a somewhat complicated process, whereby one "physically" change the LaF in question (bytecode manipulates it), injecting the laf-widget stuff into the UI delegates - and I still don't know how the JTabbedPane or TabbedPaneUI is actually modulated to inject that icon/button.