Hi guys, I got a question about Java coding in general...

In some sample codes there are methods and classes declared WITHIN other methods and/or classes....

I've never heard/red about this...what effect does this kind of programming have? Wouldn't it be better to write down classes in a seperate file and methods side by side and not within each other (like every book tells you)? What are the advantages and disadvantages of this kind of programming?

Here's an example of what I mean:

Handler mHandler = new Handler() {
    public void handleMessage(android.os.Message msg) {
        TextView textView = (TextView) findViewById(R.id.description);
        textView.setText(mRoad.mName + " " + mRoad.mDescription);
        MapOverlay mapOverlay = new MapOverlay(mRoad, mapView);
        List<Overlay> listOfOverlays = mapView.getOverlays();
        listOfOverlays.clear();
        listOfOverlays.add(mapOverlay);
        mapView.invalidate();
    };
};