Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();

我在JBuild4.0,(tomcat5.0)已将C:\Tomcat 5.0\common\endorsed\xml-apis.jar导入,然后编写document1.java

我的document1.java程序如下:

package com.deitel.advjhtp1.servlets;
import java.io.*;
import javax.xml.parsers.*;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.*;
import org.xml.sax.*;

public class document1 {

  public document1() {
  Document doc;
  DocumentBuilder builder;
  Element root;

  DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();
  factory.setValidating(true);
  try{
       builder=factory.newDocumentBuilder();
       doc=builder.newDocument();
       }catch(ParserConfigurationException pce)
       {
        pce.printStackTrace();
       }

   root=doc.createElement("root");
  }
}

提示: root=doc.createElement("root");这句话错误
"document1.java": Error #: 553 : variable doc might not have been initialized at line 31, column 9

请高手赐教!!!!