Question

I’m just starting out on android and my java is verry rusty. I can’t remember ever seeing a function nested in another function like this before. Could somebody explain to me exactly what final does and explain why you would nest a function in another like this?

private final Handler handler = new Handler() {
        @Override
        public void handleMessage(final Message msg) {
            Log.v(Constants.LOGTAG, " " + ReviewList.CLASSTAG + " worker thread done, setup ReviewAdapter");
            progressDialog.dismiss();
            if ((reviews == null) || (reviews.size() == 0)) {
                empty.setText("No Data");
            } else {
                reviewAdapter = new ReviewAdapter(ReviewList.this, reviews);
                setListAdapter(reviewAdapter);
            }
        }
    };   

Answer 1

• This is an Anonymous Class.
  What is actually happening is that a
  subclass of Handler is being
  created with an overridden
  handleMessage function.

  One of the most elegant things about
  anonymous classes is that they allow
  you to define a one-shot class exactly
  where it is needed. In addition,
  anonymous classes have a succinct
  syntax that reduces clutter in your
  code.

• You also asked “Could somebody
  explain to me exactly what final
  does”. A nice explanation can be
  found here.

  In the case of your example the final keyword stops anybody from being able to assign a new instance / null the instance of the variable “handler” meaning I cannot write the line handler =
null; or handler = new Handler() {
... } after your example code snippet.