How can i get a List of all classes which implemets a specific Interface in Android

In java (NetBeans) i realized it with...

    ClassPathLoader pathLoader = new ClassPathLoader(".");
try {
//get Classes
Hashtable ht = pathLoader.getClasses();
Set s = ht.keySet();
Iterator iter = s.iterator();
String fullName = null;
    while(iter.hasNext()) {
        try {
        fullName = (String) iter.next();
        //create class
        Class cls = Class.forName(fullName);
        //get interface from the class
        Class[] interfaces = cls.getInterfaces();
        for(int i = 0; i < interfaces.length; i++) {
        if(interfaces[i].getName().equals("IMyObserver.IFeature")) {

        //Field field = cls.getDeclaredField("LOCATION");
        //String location = (String)field.get(null);
        Constructor cons2 = cls.getDeclaredConstructor(List.class);

        Object oo = cons2.newInstance(qList);

        System.out.println(fullName);
        }
    }

This works very well, but in android does not work. I think the problem is at the ClassPath... ?!?! have anyone a idea? thx