Android: runnables in different class files

I am creating an android app and I am connecting and exchanging data with a remote server. Up to now, I have been using threads and handlers withing my activity class to interface with the server, but the code is getting increasingly messy and long. I believe that having more classes would make it (the code) easier to manage.

This is probably a large gap in my programming knowledge, but I can't figure out how to put runnables in different classes and then have them return messages to the main activity.

Thankyou in advance, sample code is preferred in answers.

You can pass a handler from the activity to the second class, and pass a message through it when needed.

public class MyActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstance) {
        // ....
        Handler myHandler = new Handler() {
            @Override
            public void handleMessage (Message msg) {
                doCoolStuffWhenMessageReceived();
            }
        }
        MySecondClass secondClass = new MySecondClass(myHandler);
        // ....
    }
}

public class MySecondClass {
    private Handler handler;
    public MySecondClass(Handler handler){
        this.handler = handler;
    }

    private void someMethodToCallActivity() {
        handler.sendEmptyMessage(0);
    }

}