安卓下面可以通过Runnable和Handler来完成时钟功能，代码如下：

public class MyActivity extends Activity {
    private Handler time_handler = new Handler();
    private int count = 0;
    private Runnable time_runnable = new Runnable() {
        public void run() {
            try  {
                ++count;
                Toast.makeText(MyActivity.this,String.format("第%d秒",count),Toast.LENGTH_SHORT).show();
            }
            finally {
                time_handler.postDelayed(this, 1000);
            }
        }
    };

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        time_handler.postDelayed(time_runnable,1000);
    }
}