Call java reflection method invoke on classes that were copied after a specific amount of time to a folder

I'm trying to invoke methods of classes that I have copied to my folder (where the other classes already were) but when I run the program, it only displays the methods and the results of the classes that were already in that specific folder. I used Thread.sleep(...) in order to have time to copy thw particular class files that I want to add, let's say, after 5 seconds. Here's my code:

private static ClassLoader cl;

public static void main(String... args) throws NoSuchFieldException,
        SecurityException, InstantiationException, IllegalAccessException,
        IllegalArgumentException, InvocationTargetException,
        InterruptedException, IOException {



    File dest = new File("D:\\....\\");
    File source = new File("D:\\....\\");

    List<String> classNames = new ArrayList<>();

    try {
        File[] files = dest.listFiles();
        for (File f : files) {
            classNames.add(f.getName().substring(0, f.getName().indexOf(".")));
        }

        @SuppressWarnings("deprecation")
        URL url = dest.toURL();
        URL[] urls = new URL[] { url };

        cl = new URLClassLoader(urls);

        List<Class<?>> classes = new ArrayList<>();
        for (String className : classNames) {
            classes.add(cl.loadClass(className));
        }

        for (Class<?> cla : classes) {
            Method[] allMethods2 = cla.getDeclaredMethods();
            for (Method method : allMethods2) {
                FileUtils.copyDirectory(source, dest); // copies the files from one directory to another
                Object obj = cla.newInstance();
                method.invoke(obj);
                Thread.sleep(5000);

            }
        }
        catch (MalformedURLException e) {
        } 
        catch (ClassNotFoundException e) {
        }
    }
}