请教把Dialog声明为final有什么好处

public class AlertDialogStudy extends Activity {
14        /** Called when the activity is first created. */
15        @Override
16        public void onCreate(Bundle savedInstanceState) {
17            super.onCreate(savedInstanceState);
18            setContentView(R.layout.main);
19     
20            // get button
21            Button btnShow = (Button)findViewById(R.id.btn_show);
22            btnShow.setOnClickListener(new View.OnClickListener() {
23     
24                @Override
25                public void onClick(View v) {
26                    AlertDialog.Builder builder = new AlertDialog.Builder(v.getContext());
27                    builder.setTitle("Auto-closing Dialog");
28                    builder.setMessage("After 2 second, this dialog will be closed automatically!");
29                    builder.setCancelable(true);
30     
31                    final AlertDialog dlg = builder.create();
32     
33                    dlg.show();
34     
35                    final Timer t = new Timer();
36                    t.schedule(new TimerTask() {
37                        public void run() {
38                            dlg.dismiss(); // when the task active then close the dialog
39                            t.cancel(); // also just top the timer thread, otherwise, you may receive a crash report
40                        }
41                    }, 2000); // after 2 second (or 2000 miliseconds), the task will be active.
42     
43                }
44            });
45        }
46    }