Exception in thread "AWT-EventQueue-0" java.lang.NullPointerExcep

//Code//

/*
* Bike.java
*
* Created on 6. maj 2007, 16:21
*
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
*/
import java.awt.*;
import java.awt.event.*;

import javax.swing.*;
/**
*
* @author Joshlo
*/
public class Bike extends javax.swing.JFrame {
   
    private JFrame frame;
    private JPanel gearpanel;
    private JPanel speedpanel;
    private JPanel pulsepanel;
    private Graphics g;
    private int x1;
    private int x2;
    private int y1;
    private int y2;
    private int y3;
   
    /** Creates a new instance of Bike */
    public Bike() {
        createFrame();
    }
   
    public void createFrame()
    {
        g.setColor(Color.GRAY);
       
        frame = new JFrame();
       
        frame.setTitle("Bike");
        frame.setSize(900,650);
        frame.setResizable(false);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       
        gearpanel.setSize(800,200);
        gearpanel.setLocation(100,0);
        gearpanel.setBackground(Color.BLACK);
        geargrid();
       
        speedpanel.setSize(800,200);
        speedpanel.setLocation(100,210);
        speedpanel.setBackground(Color.BLACK);
       
        pulsepanel.setSize(800,200);
        pulsepanel.setLocation(100,420);
        pulsepanel.setBackground(Color.BLACK);
       
        frame.getContentPane().add(gearpanel);
        frame.getContentPane().add(speedpanel);
        frame.getContentPane().add(pulsepanel);
       
        frame.setVisible(true);
    }
   
    public void geargrid()
    {
        g.drawLine(100,0,900,0);
        g.drawLine(100,25,900,25);
        g.drawLine(100,50,900,50);
        g.drawLine(100,75,900,75);
        g.drawLine(100,100,900,100);
        g.drawLine(100,125,900,125);
        g.drawLine(100,150,900,150);
        g.drawLine(100,175,900,175);
        g.drawLine(100,200,900,200);
       
        int y4 = gearpanel.getWidth() / 25;
       
        for(y3 = 0; y3 <= y4; y3++)
        {
            x1 = 0;
            x2 = 0;
            y1 = 0;
            y2 = 200;
            g.drawLine(x1,y1,x2,y2);
            x1 = x1 + 25;
            x2 = x2 + 25;
            y1 = 0;
            y2 = 200;
        }
    }
   
    public static void main(String []args) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Bike();
            }
        });
    }
}

//fejl//

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at Bike.createFrame(Bike.java:37)
        at Bike.<init>(Bike.java:32)
        at Bike$1.run(Bike.java:96)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)


håber der er en der kan hjælpe mig.