testing stack overflow. working of stack

how to work on stack. i am just showing example for my team.. dont reply to this this is just for sample pls dont reply to this

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    arrayListContact=new ArrayList<Contacts>();
    listContacts = (ListView)findViewById(R.id.listView);
    contactAddButton = (Button)findViewById(R.id.contactAddButton);

    contactAddButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Intent intent = new Intent(MainActivity.this, Data.class);
            startActivityForResult(intent, 1);


        }
    });