It is old Sun technology that Sun abandoned to work only on Java and if you are familiar with how bad and ugly the original Java UIs were (AWT, Applets, etc.) you already know what it looks like.
To match modern Android UIs they have to rip out a lot of chrome and needless borders and decoration and make the whole thing a lot cleaner, then redo everything to try to follow a consistent design grid of touchable items. Android designs follow a 48dp grid (dp being a pixel that scales with screen density) to keep things consistent and the right size to touch. In the screenshots above you often see things like inconsistent spacing and tiny microscopic checkboxes (which are not even consistent checkboxes with the rest of Android so increase user friction).