title: In java, why is Observable's setChanged() protected?
body: <p>If a java class, say <code>classA</code>, is extending <code>classB</code>, it cannot extend <code>Observable</code>. But if the <code>setChanged()</code> function were public, instead of protected, we can use composition to create an instance of <code>Observable</code> in <code>classA</code>.</p>
  
  <p>I wonder what was the thought process behind making <code>setChanged()</code> protected.</p>