how to solve this type of compilation error?
<pre><code>import java.net.*;
import java.io.*;

public class DjPageDownloader {


    public URL url;
    public InputStream is = null;
    public DataInputStream dis;
    public String line;

    public static void main(String []args){
        try {
            url = new URL("http://stackoverflow.com/");
            is = url.openStream();  // throws an IOException
            dis = new DataInputStream(new BufferedInputStream(is));

            while ((line = dis.readLine()) != null) {
                System.out.println(line);
            }
        } catch (MalformedURLException mue) {
             mue.printStackTrace();
        } catch (IOException ioe) {
             ioe.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException ioe) {
                // nothing to see here
            }
        }

    }
</code></pre>

<p>this on compilation shows error as:-</p>

<pre><code>Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
    Cannot make a static reference to the non-static field url
    Cannot make a static reference to the non-static field is
    Cannot make a static reference to the non-static field url
    Cannot make a static reference to the non-static field dis
    Cannot make a static reference to the non-static field is
    Cannot make a static reference to the non-static field line
    Cannot make a static reference to the non-static field dis
    Cannot make a static reference to the non-static field line
    Cannot make a static reference to the non-static field is

    at djPageDownloader.DjPageDownloader.main(DjPageDownloader.java:16)
</code></pre>
