A Window object is a top-level window with no borders and no menubar. The default layout for a window is BorderLayout.
A window must have either a frame, dialog, or another window defined as its owner when it's constructed.
In a multi-screen environment, you can create a Window on a different screen device by constructing the Window with Window(Window, GraphicsConfiguration). The GraphicsConfiguration object is one of the GraphicsConfiguration objects of the target screen device.
ну и вот как бы описание как себя window ведет