Swing is NOT platform native, that's why SWT was developed in the first place. Swing can use native look-a-like theming but it's not the same thing as SWT's actual, truly native widgets (with native keyboard shortcuts, system services..).

wxWidgets and SWT are about as native at it can be in a cross platform GUI library. I don't see why you'd need a screenshot of the go library, it would look the same as a typical wxWidgets or SWT app, which is to say, it uses native controls, but might not be designed according to the "common" UI conventions of the platform.