Optimize code Java in activity and long operation

hello I have a problem with java and android develop a dual timer with the Runnable class.
By means of a call first the activity mRunnable and then the mRunnable1 at a distance of a few seconds. The problem is that when viewing the screen "DownTot.setText (a);" show me for a moment and then subsequently rxbytes the difference (rxbytes - rxbytes1). This is done as if the operation was slow. is there a way to optimize my code?
Here is the code below:

Code Java:

public class MainActivity extends Activity implements OnClickListener  {
 
    TextView DownTot;
    private long rxBytes;
    private long rxBytes1;
private final Runnable mRunnable = new Runnable() {
    	public void run() {
        mHandler.postDelayed(mRunnable1, 1000);
        TextView DownTot = (TextView)findViewById(R.id.downtot);
        rxBytes = (TrafficStats.getTotalRxBytes()- StartDown);
    	long a = rxBytes - rxBytes1;
    	DownTot.setText(a);
    	}
    };
 
    private final Runnable mRunnable1 = new Runnable() {
    	public void run() {
        mHandler.postDelayed(mRunnable1, 1000);
        TextView DownTot = (TextView)findViewById(R.id.downtot);
        rxBytes1 = (TrafficStats.getTotalRxBytes()- StartDown);
    	long a = rxBytes1 - rxBytes;
    	DownTot.setText(a);
    	}
    };
 
......