different between "getDocumentElement" and "getFirstChild"

The Node you get using myDoc.getFirstChild() may not be the document root if there are other nodes before the document root node - such as a comment node. Look at the example below:

import org.w3c.dom.*;public class ReadXML {    public static void main(String args[]) throws Exception{             DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();        DocumentBuilder docBuilder = docFactory.newDocumentBuilder();        // Document elements        Document doc = docBuilder.parse(new File(args[0]));        Node firstChild = doc.getFirstChild();        System.out.println(firstChild.getChildNodes().getLength());        System.out.println(firstChild.getNodeType());        System.out.println(firstChild.getNodeName());        Node root = doc.getDocumentElement();        System.out.println(root.getChildNodes().getLength());        System.out.println(root.getNodeType());        System.out.println(root.getNodeName());    }}

When parsing the following XML file:

<?xml version="1.0"?><!-- Edited by XMLSpy --><catalog>   <product description="Cardigan Sweater" product_image="cardigan.jpg">      <catalog_item gender="Men's">         <item_number>QWZ5671</item_number>         <price>39.95</price>         <size description="Medium">            <color_swatch image="red_cardigan.jpg">Red</color_swatch>            <color_swatch image="burgundy_cardigan.jpg">Burgundy</color_swatch>         </size>         <size description="Large">            <color_swatch image="red_cardigan.jpg">Red</color_swatch>            <color_swatch image="burgundy_cardigan.jpg">Burgundy</color_swatch>         </size>      </catalog_item>       </product></catalog>

gives the following result:

08#comment31catalog

But if I remove the comment, it gives:

31catalog31catalog