android - 刚开始解析 XML

Question

在下面的代码中，当我使用 getNodeValue() 时，我什么也没得到，但是当我使用 getTextContent() 时，它会返回它的内容以及它的子内容。谁能告诉我为什么 getNodeValue() 不起作用？XML 在这里给出：

http://developer.android.com/training/basics/network-ops/xml.html

    DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost("http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest");

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            InputStream is = httpEntity.getContent();

            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = factory.newDocumentBuilder();
            Document doc = builder.parse(is, null);

            NodeList rootNode = doc.getElementsByTagName("entry");

            for (int i = 0; i < rootNode.getLength(); i++)
            {
                Node node = rootNode.item(i);
                if(node.getNodeType()==Node.ELEMENT_NODE){
                    Element element = (Element)node;

                    String title = element.getElementsByTagName("title").item(0).getTextContent();
                    String author = element.getElementsByTagName("author").item(0).getNodeValue();
                    String summary = element.getElementsByTagName("summary").item(0).getNodeValue();                        
                    String result = title+"\n"+author+"\n"+summary+"";
                    list.add(result);
                }                               
            }