title: different between "getDocumentElement" and "getFirstChild"
body: <p>I have the following <code>Document</code> object - <code>Document myDoc</code>.</p>
  
  <p><code>myDoc</code> holds an <code>XML</code> file by...</p>
  
  <pre><code>myDoc = DocumentBuilderFactory.newInstance()
              .newDocumentBuilder().parse(file);
  </code></pre>
  
  <p>Now I want to get the root of the XML file.  Is there any difference between </p>
  
  <pre><code>Node firstChild = this.myDoc.getFirstChild() 
  </code></pre>
  
  <p>and</p>
  
  <pre><code>Node firstChild = (Node)myDoc.getDocumentElement()
  </code></pre>
  
  <p>In the first way, <code>firstChild</code> holds a node root of an <code>XML</code> file but it will not have the depth of <code>Node</code>. However, in the second way, <code>firstChild</code> will be the root with all of the depth.</p>
  
  <p>For example, I have the following XML</p>
  
  <pre><code>&lt;inventory&gt;
      &lt;book num="b1"&gt;
      &lt;/book&gt;
      &lt;book num="b2"&gt;
      &lt;/book&gt;
      &lt;book num="b3"&gt;
      &lt;/book&gt;
  &lt;/inventory&gt;
  </code></pre>
  
  <p>and <code>file</code> holds it.</p>
  
  <p>In the 1st case, <code>int count = firstChild.getChildNodes()</code>  gives  <code>count = 0</code>. </p>
  
  <p>The 2nd case will give <code>count = 3</code>.</p>
  
  <p>Am I right?</p>