Duvido com Liquid and feel

public static void main(String[] args) throws Exception {
        System.setProperty("sun.java2d.ddscale", "true");
        UIManager.setLookAndFeel("com.birosoft.liquid.LiquidLookAndFeel");
        UIManager.addPropertyChangeListener(new PropertyChangeListener(){

            public void propertyChange(PropertyChangeEvent event) {
                Object newLF = event.getNewValue();
                if (!(newLF instanceof LiquidLookAndFeel)) {
                    try {
                        UIManager.setLookAndFeel(new LiquidLookAndFeel());
                    }
                    catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        });
        Class mainClass = null;
        if (args[0].toLowerCase().endsWith(".jar")) { // aqui esta o problema
            File file = new File(args[0]);
            JarFile jarFile = new JarFile(file);
            Manifest manifest = jarFile.getManifest();
            String mainClassName = manifest.getMainAttributes().getValue("Main-Class");
            Class class_ = Launcher.class;
            URLClassLoader loader = new URLClassLoader(new URL[]{file.toURL()}, class_.getClassLoader());
            mainClass = Class.forName(mainClassName, true, loader);
        } else {
            mainClass = Class.forName(args[0]);
        }
        Class[] arrclass = new Class[1];
        Class class_ = String.class;
        arrclass[0] = class_;
        Method m = mainClass.getMethod("main", arrclass);
        String[] copyOfArgs = new String[args.length - 1];
        for (int i = 1; i < args.length; ++i) {
            copyOfArgs[i - 1] = args[i];
        }
        m.invoke(mainClass, copyOfArgs);
    }