A huge advantage of WPF over, say, WinForms is its composability. To quote Programming WPF:
One level up, WPF provides its “content model,” which allows any control to host any group of other controls. You don’t have to build special
BitmapButtonorIconComboBoxclasses; you put as many images, shapes, videos, 3D models, or whatever into a Button (or aComboBox,ListBox, etc.) as suit your fancy.
Are there any cross-platform GUI frameworks (preferably with Java bindings) out there which also let you do this?