public synchronized Collection getRefClasses() {
        ClassFile cf = getClassFile2();
        if (cf != null) {
            ClassMap cm = new ClassMap() {
                public void put(String oldname, String newname) {
                    put0(oldname, newname);
                }

                public Object get(Object jvmClassName) {
                    String n = toJavaName((String)jvmClassName);
                    put0(n, n);
                    return null;
                }

                public void fix(String name) {}
            };
            cf.renameClass(cm);
            return cm.values();
        }
        else
            return null;
    }