title: No error calling textView.setText from non UI-Thread. Why?
body: <p>I wrote the following Code which basically starts a Thread from which the text of a TextView is changed.  </p>
  
  <p>I was expecting an error because I access a TextTiew (UI-element) from another Thread than the main-Thread.  </p>
  
  <p>But it works fine. Thought this shouldn't be possible as far as I know.<br>
  I don't get it, what am I missing? </p>
  
  <pre><code>public class MainActivity extends Activity {
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          TextView tv = (TextView) findViewById(R.id.view1);
          tv.setText(Thread.currentThread().getName());
  
          Thread theThread = new Thread(new aRunnable(tv));
          theThread.start();      
      }
      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
          // Inflate the menu; this adds items to the action bar if it is present.
          getMenuInflater().inflate(R.menu.activity_main, menu);
          return true;
      }
  }
  </code></pre>
  
  <hr>
  
  <pre><code>public class ARunnable implements Runnable{     
      TextView tv;    
      public ARunnable(TextView tv){
          this.tv = tv;
      }   
      @Override
      public void run() {
          tv.setText(tv.getText()+"----" + Thread.currentThread().getName()); 
      }
  
  }
  </code></pre>