Runtime error to get the attribute value of an element

Question

mydoc.xml
=========
<?xml version = "1.0"?>
<persons>
     <person name="Joe" age="22" />
</persons>
In mydox.xml, I want to get the attribute values of element person. Of course,
in the actual XML file, it is more complicated.
However, I get the following run-time error,
Exception in thread "main" java.lang.NullPointerException
at ParserTest.main(ParserTest2.java:18) on line element.hasAttribute("name")
import java.io.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.*;
import javax.xml.transform.stream.*;
import org.w3c.dom.*;
import javax.xml.parsers.*;
import org.xml.sax.*;
public class ParserTest2
     public static void main(String[] args) throws ParserConfigurationException, SAXException
          String xmlFile = "mydoc.xml";
          doc = getDocumentFromFile(xmlFile);
          Element element = doc.getElementById("person");
          //Exception in thread "main" java.lang.NullPointerException
          if (element.hasAttribute("name"))
          {     System.out.println("attribute = " + element.getAttribute("name"));
     public static Document getDocumentFromFile(String xmlFile)
               try
                    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
                    DocumentBuilder builder = factory.newDocumentBuilder();
                    Document doc = builder.parse(new File(xmlFile));
                    return doc;
               catch(IOException e)
               {     e.printStackTrace();
                    return null;
               catch(SAXException e)
               {     e.printStackTrace();
                    return null;
               catch(ParserConfigurationException e)
               {     e.printStackTrace();
                    return null;
     private static Document doc;
any ideas? Thanks!!

Answer 1

[url http://java.sun.com/j2se/1.4.2/docs/api/java/lang/NullPointerException.html]java.lang.NullPointerException
Thrown when an application attempts to use null in a case where an object is required. These include:
Calling the instance method of a null object.
Accessing or modifying the field of a null object.
Taking the length of null as if it were an array.
Accessing or modifying the slots of null as if it were an array.
Throwing null as if it were a Throwable value.
You know what line it happens on, so you know which of these cases applies. So you know that variable "element" is null at that point. How could it come to be null? You assign to it only once, two lines above. How could that assignment be null? Check the documentation for [url http://java.sun.com/j2se/1.4.2/docs/api/org/w3c/dom/Document.html#getElementById(java.lang.String)]org.w3c.dom.Document.getElementById().
Repeat every time you get one of those exceptions.