As it was already mentioned DOM-document contains the only root element. The root in its turn consists of nodes. XML-element are concrete types of those node. Except elements nodes can be also comments, text, attribute, notation, processing instruction and event the document it self. Since when we request a child from an element we get a node of unknown type, we may use its getNodeValue() method to indicates its type and to cast to corresponding interface:

 import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.*;

/**
 * This sample program shows how to browse through DOM-tree,
 * determine the types of DOM-nodes and printing their 
 * specific contents.
 */

public class Test {
  public static void main(String[] args) {
    try {
      // first of all we request out 
      // DOM-implementation:
      DocumentBuilderFactory factory = 
        DocumentBuilderFactory.newInstance();
      // then we have to create document-loader:
      DocumentBuilder loader = factory.newDocumentBuilder();

      // loading a document...
      Document document = loader.parse("sample.xml");
      
      // access to root element:
      Element purchaseOrder = document.getDocumentElement();
      
      // print a document element content:
      printElement(purchaseOrder, "");
            
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }
  
  public static final void printElement(Element element, String indent) {
    System.out.println("Element '" + element.getNodeName() + "'");
    
    NodeList children = element.getChildNodes();
    for (int i = 0; i < children.getLength(); i++) {
      Node child = children.item(i);
      
      switch (child.getNodeType()) {
      case Node.ELEMENT_NODE:
        // recursive call for all element children:
        printElement((Element) child, indent + "\t");
        break;
      case Node.ATTRIBUTE_NODE:
        Attr attr = (Attr) child;
        System.out.println("\tAttribute: '" + 
          attr.getName() + "' = '" + attr.getValue() + "'");
        break;
      case Node.COMMENT_NODE:
        Comment comment = (Comment) child;
        System.out.println("\tComment: '" + comment.getData() + "'");
        break;
      case Node.CDATA_SECTION_NODE:
        CharacterData cdata = (CharacterData) child;
        System.out.println("\tCDatat: '" + cdata.getData() + "'");
        break;
      case Node.TEXT_NODE:
        Text text = (Text) child;
        System.out.println("\tText: '" + text.getData() + "'");
        break;
      // ... all cases remaining ...
      default:
        System.out.println("\tUnknown node type: '" 
          + child.getNodeType() + "'");
        break;
      }
    }
  }
}