public static File getPreferencesFile() {
	if( prefsFile == null ) {
	    String userHome = System.getProperty("user.home");
	    if(userHome == null) {
		throw new IllegalStateException("user.home==null");
	    }
	    File home = new File(userHome);
	    prefsFile = new File(home, prefsFileName);
	    if(!prefsFile.exists()) {
		try {
		    if(!prefsFile.createNewFile()) {
			throw new IllegalStateException(prefsFile.toString());
		    }
		} catch( Exception e ) {
		    e.printStackTrace();
		}
	    }
	}
	return prefsFile;
    }