title: difficulty understanding ActionBar and ifRoom
body: <pre><code>private void setUpActionBar() {
  // Make sure we're running on Honeycomb or higher to use ActionBar APIs
  if (Build.VERSION.SDK_INT &gt;= Build.VERSION_CODES.HONEYCOMB) {
      ActionBar actionBar = getActionBar();
      actionBar.setDisplayHomeAsUpEnabled(true);
  }
  }
  </code></pre>
  
  <p>What is ActionBar ? Is it a pop-up window or an activity or something else ?</p>
  
  <p>One more question, why do we need to use 'ifRoom' argument in android:showAsAction attribute ?</p>