title: What is audio focus in Android class AudioManager?
body: <p>The <code>AudioManager</code> class has a method <code>abandonAudioFocus()</code> and another method <code>requestAudioFocus()</code>. I wonder what is audio focus? And what happens if an <code>AudioManager</code> object gets the audio focus or lost the audio focus?  </p>
  
  <p>Thank you!</p>