different between “getDocumentElement” and “getFirstChild”

Question

I have the following Document object - Document myDoc.

myDoc holds an XML file by...

myDoc = Document         


        

Answer 1

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:

   
      
         QWZ5671
         39.95
         
            Red
            Burgundy
         
         
            Red
            Burgundy
         
          
   

gives the following result:

0
8
#comment
3
1
catalog

But if I remove the comment, it gives:

3
1
catalog
3
1
catalog