Graphing Applet (Strip)

Dear friend i have the following applet code, i need your support to reviews this code because with my symantec visual cafe show severals errors on the compilation time.

Thanks by cheking my code.

thanks,

Jairo

**************Applet begin here*********************

import java.applet.Applet;
import java.net.*;
import java.awt.*;
import java.awt.Graphics;
import java.awt.event.*;
import java.util.Enumeration;

public class StripChart extends Applet implements Runnable
{
 static int chartWidth = 300;
 static int chartHeight = 120;

 static Color chartFG = new Color(0x336699);
 static Color chartBG = new Color(0xFFCC33);

    private Image graph;
    private Graphics graphGraphics;
    private Graphics screenGraphics;

    private Thread runner;

    long currentTick = -1;

    public StripChart() {
        setBackground(chartBG);
        setForeground(chartFG);
    }

    public void addNotify() {
        super.addNotify();
        try {
            screenGraphics = getGraphics();
            graph = createImage(chartWidth, chartHeight);
            graphGraphics = graph.getGraphics();
            graphGraphics.setColor(chartBG);
            graphGraphics.fillRect(0,0,chartWidth,chartHeight);
        } catch (Exception e) { throw new Error("Hosed!"); }
    }
    public Dimension getPreferredSize() { return new Dimension(chartWidth, chartHeight); }

    public void setBackground(Color bg) { chartBG = bg; }
    public void setForeground(Color fg) { chartFG = fg; }
    public Color getBackground() { return chartBG; }
    public Color getForeground() { return chartFG; }


    private int value;  // only here to implement a fake data feed

    /** this should ask the 'world' for the next point to be charted */
    protected int getNextChartValue()
    {
        int K = 8; // max +/- change per tick
        int delta = ((int)( Math.random()*(2*K+1))) - K;
        value -= delta;
        if (value<0) value = 0;
        if (value>=chartHeight) value = chartHeight-1;
        return value;
    }

    private int getImageOffset() {
        if (currentTick<chartWidth) return 0;
        return (int) ((currentTick+1) % chartWidth);
    }

    private void setNextPoint(int val) {
        if (val<0) val=0;
        if (val>=chartHeight) val=chartHeight-1;
        int x = (int) (++currentTick % chartWidth);
        graphGraphics.setColor(chartBG);
        graphGraphics.drawLine(x,0, x,chartHeight-val);
        graphGraphics.setColor(chartFG);
        graphGraphics.drawLine(x,chartHeight-val, x,chartHeight);
        paint(screenGraphics);
    }

    public void run() {
        long mark = System.currentTimeMillis();

        while (runner!=null) {

            setNextPoint(getNextChartValue());

            // just some timing stuff
            if (currentTick % chartWidth == chartWidth - 1) {
                long now = System.currentTimeMillis();
                double elapsed = (now - mark) / 1000.0;
                double frames = chartWidth;
                int fps = (int) (frames / elapsed + 0.5);
                showStatus("fps = " + fps);
                mark = now;
            }
        }
    }

    public void    init() { if (isActive()) showStatus(getAppletInfo()); }
    public void   start() { runner=new Thread(this); runner.start(); }
    public void    stop() { runner=null; }
    public void destroy() { }

    public void update(Graphics g) { paint(g); }
    public void  paint(Graphics g) {
        if (graph==null) return;
        int xoff = getImageOffset();
        g.drawImage(graph,     -xoff, 0, chartWidth, chartHeight, null);
        g.drawImage(graph, chartWidth-xoff, 0, chartWidth, chartHeight, null);
    }

    public final String getAppletInfo()
    { return "StripChart"; }

    public boolean mouseMove(Event evt, int x, int y)
    {   showStatus(getAppletInfo());
        return super.mouseMove(evt, x, y);
    }
}

class StripChartApp extends Frame implements AppletStub, AppletContext
{
 // AppletStub stuff
 public boolean isActive() { return false; }
 public URL getDocumentBase() { return null; }
 public URL getCodeBase() { return null; }
 public String getParameter(String name) { return null; }
 public AppletContext getAppletContext() { return this; }
 public void appletResize(int width, int height) {}

 // AppletContext stuff
 public Applet getApplet(String name) { return null; }
 public Enumeration getApplets() { return null; }
 public AudioClip getAudioClip(URL url) { return null; }
 public Image getImage(URL url) { return null; }
 public void showDocument(URL url) {}
 public void showDocument(URL url, String target) {}
 public void showStatus(String txt)
    {if (status!=null) status.setText(txt); }

    static private Applet applet = null;
    static private Label  status = null;

    StripChartApp(String title) {
        super(title);
        setLayout(new BorderLayout());
        add("Center", applet=new StripChart());
        add("South",  status=new Label());
        applet.setStub(this);
    }
    public static void main(String args[]) {
        Frame frame = new StripChartApp("StripChart");
        frame.pack();
        frame.show();
        applet.init();
        applet.start();
        frame.addWindowListener(new WindowAdapter()
            { public void windowClosing(WindowEvent e) { System.exit(0); } });
    }
}

*******applet end here******************