W3C模块不存在

Question

我试着做Y！为了使用BlueJ学习，天气XML解析。当我编译课程时，BlueJ给了我错误：package org.w3c does not exist

以下是代码：

import java.net.URL;
import java.io.InputStream;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.w3c.*;

public class WeatherApp
{
    public static void main(String[] args)
    {
        URL xmlURL = new URL("http://weather.yahooapis.com/forecastrss?w=22722924&u=c");
        InputStream xml = xmlURL.openStream();
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse(xml);
        xml.close();

        System.out.println(doc);
    }
}

这里可能出现什么问题？以及如何解决它？感谢