private static boolean isXWindowSystem() {
		if( isXWindowSystem == null )
			isXWindowSystem = Toolkit.getDefaultToolkit().getClass().getName().endsWith( ".XToolkit" );
		return isXWindowSystem;
	}
Checks whether native library is loaded/available.
<p>
<b>Note</b>: It is required to invoke this method before invoking any other
             method of this class. Otherwise, the native library may not be loaded.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatNativeLinuxLibrary.java