Proxy pattern concrete class hiding implementation details

I have been reading about java proxy pattern and invocation handler and everywhere it is seen that the concrete class construction is available to the client.

For example,

//TwitterService service = (TwitterService) SecurityProxy.newInstance(new TwitterStub());
TwitterService service = new TwitterStub();
System.out.println(service.getTimelinePosts("abc"));

User can create an instance of TwitterStub directly and access the methods. I was wondering if there was a way of not exposing the or avoiding the construction of the concrete class via the client ?

Is there a better way ?