Should Java Assert that Network I/O Can't Occur on the UI Thread?

Should Java Assert that Network I/O Can't Occur on the UI Thread?: "Doing network I/O on the user interface (UI) thread is bad. Most developers know that and can tell you why; unfortunately, it's still done. At this year's JavaOne, one of the keynote JavaFX demos bombed because the network was slow, something that would be forgivable had the entire application's UI not frozen, which required it to be restarted, only to trip up again a few minutes later."