runOnUiThread, runs the specified action on the UI thread

package com.example.androidrunnable;

import android.os.Bundle;
import android.app.Activity;
import android.widget.TextView;

public class MainActivity extends Activity {
 
 static TextView prompt;
 static int counter;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_main);
        prompt = new TextView(this);
        setContentView(prompt);
        
        prompt.setText("Hello");
        
        Thread myThread = new Thread(myRunnable);
        myThread.start();
    }

    Runnable myRunnable = new Runnable(){

  @Override
  public void run() {
   counter = 0;
   while(true){
    try {
     Thread.sleep(1000);
     runOnUiThread(new Runnable(){

      @Override
      public void run() {
       prompt.setText(String.valueOf(counter));
      }
      
     });
     counter++;
    } catch (InterruptedException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
    }
   }
  } 
    };

}