Collection<Class<?>> getAllInterfaceImplementations(String pathToJar,
                                                    Class<?> interfaceType) throws Exception {
    JarFile jarFile = new JarFile(pathToJar);
    Enumeration<JarEntry> e = jarFile.entries();

    URL[] urls = {new URL("jar:file:" + pathToJar + "!/")};
    URLClassLoader cl = URLClassLoader.newInstance(urls);

    Collection<Class<?>> classes = new ArrayList<>();
    while (e.hasMoreElements()) {
        JarEntry je = e.nextElement();
        if (je.isDirectory() || !je.getName().endsWith(".class")) {
            continue;
        }

        String className = je.getName().substring(0, je.getName().length() - ".class".length());
        className = className.replace('/', '.');
        Class type = cl.loadClass(className);
        if (interfaceType.isAssignableFrom(type))
            classes.add(type);
    }

    return classes;
}

String pathToJar = "<путь до JAVA_HOME>/rt.jar";

for (Class<?> type : getAllInterfaceImplementations(pathToJar, Collection.class))
    System.out.println(type.getName());