public static boolean isFullScreen( Component c ) {
		GraphicsConfiguration gc = c.getGraphicsConfiguration();
		GraphicsDevice gd = (gc != null) ? gc.getDevice() : null;
		Window fullScreenWindow = (gd != null) ? gd.getFullScreenWindow() : null;
		return (fullScreenWindow != null && fullScreenWindow == SwingUtilities.windowForComponent( c ));
	}
Returns whether the given component is in a window that is in full-screen mode.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatUIUtils.java