Java graphics drawing doesn't show up on drawing panel

Question

I'm starting a really simple java program. The user can select a shape, size, fill (boolean), lineColor and fillColor from a menu, and then click and drag to draw the selected object on the screen. At this point, I'm just trying to figure out why nothing is drawing on the screen. In the run method, I have a simple rectangle drawn at 200,200, but nothing is appearing on the panel. I'm confident that i can get the rest of the program working just fine once I figure out why nothing is drawing Any idea what I'm doing wrong?

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;
import java.lang.*;
import java.awt.Rectangle;

public class E3G04 extends Frame implements WindowListener, ActionListener, ItemListener, MouseListener, MouseMotionListener, Runnable
{
    volatile String type = "rectangle";
    volatile Boolean fill = true;
    Color lineColor = Color.BLACK;
    Color fillColor = Color.BLACK;
    int size = 1;

    private Graphics obj;
    Point start = new Point(100,100);
    Point cur = new Point(100,100);
    Point end = new Point(100,100);

    Panel drawingpanel;
    Thread thread = new Thread(this);
    boolean running = true;

    MenuBar mb = new MenuBar();
        Menu fileMenu = new Menu("File");
            MenuItem newItem = new MenuItem("New (Ctrl-N)");
            MenuItem quitItem = new MenuItem ("Quit (Ctrl-Q)");
        Menu drawMenu = new Menu("Draw");
            Menu typeMenu = new Menu("Type");
                CheckboxMenuItem ovalItem = new CheckboxMenuItem("Oval (Ctrl-O)");
                CheckboxMenuItem rectItem = new CheckboxMenuItem("Rectangle (Ctrl-R)", true);
                CheckboxMenuItem lineItem = new CheckboxMenuItem("Line (Ctrl-L)");
            Menu fillMenu = new Menu ("Fill");
                CheckboxMenuItem fillItem = new CheckboxMenuItem("Fill", true);
                CheckboxMenuItem noFillItem = new CheckboxMenuItem("No Fill");
            Menu colorMenu = new Menu ("Color");
                CheckboxMenuItem blackLineItem = new CheckboxMenuItem("Black Line", true);
                CheckboxMenuItem redLineItem = new CheckboxMenuItem("Red Line");
                CheckboxMenuItem orangeLineItem = new CheckboxMenuItem("Orange Line");
                CheckboxMenuItem yellowLineItem = new CheckboxMenuItem("Yellow Line");
                CheckboxMenuItem greenLineItem = new CheckboxMenuItem("Green Line");
                CheckboxMenuItem blueLineItem = new CheckboxMenuItem("Blue Line");
                CheckboxMenuItem purpleLineItem = new CheckboxMenuItem("Purple Line");
                CheckboxMenuItem grayLineItem = new CheckboxMenuItem("Gray Line");
                CheckboxMenuItem blackFillItem = new CheckboxMenuItem("Black Fill", true);
                CheckboxMenuItem redFillItem = new CheckboxMenuItem("Red Fill");
                CheckboxMenuItem orangeFillItem = new CheckboxMenuItem("Orange Fill");
                CheckboxMenuItem yellowFillItem = new CheckboxMenuItem("Yellow Fill");
                CheckboxMenuItem greenFillItem = new CheckboxMenuItem("Green Fill");
                CheckboxMenuItem blueFillItem = new CheckboxMenuItem("Blue Fill");
                CheckboxMenuItem purpleFillItem = new CheckboxMenuItem("Purple Fill");
                CheckboxMenuItem grayFillItem = new CheckboxMenuItem("Gray Fill");
            Menu sizeMenu = new Menu("Size");
                CheckboxMenuItem oneItem = new CheckboxMenuItem("One", true);
                CheckboxMenuItem twoItem = new CheckboxMenuItem("Two");
                CheckboxMenuItem threeItem = new CheckboxMenuItem("Three");
                CheckboxMenuItem fourItem = new CheckboxMenuItem("Four");
                CheckboxMenuItem fiveItem = new CheckboxMenuItem("Five");

    protected E3G04()
    {

        // Add everything to the menu bar and then
        // add the menu bar to the frame
        mb.add(fileMenu);
        mb.add(drawMenu);
        fileMenu.add(newItem);
        fileMenu.add(quitItem);
        drawMenu.add(typeMenu);
        drawMenu.add(fillMenu);
        drawMenu.add(colorMenu);
        drawMenu.add(sizeMenu);
        typeMenu.add(ovalItem);
        typeMenu.add(rectItem);
        typeMenu.add(lineItem);
        fillMenu.add(fillItem);
        fillMenu.add(noFillItem);
        if (fill && type != "line")
        {       
            enableAllColors();
        }
        else
        {
            disableFillColor();
        }
        sizeMenu.add(oneItem);
        sizeMenu.add(twoItem);
        sizeMenu.add(threeItem);
        sizeMenu.add(fourItem);
        sizeMenu.add(fiveItem);                 
        setMenuBar(mb); 

        //Set all of the listeners  
        newItem.addActionListener(this);
        quitItem.addActionListener(this);
        ovalItem.addItemListener(this);
        rectItem.addItemListener(this);
        lineItem.addItemListener(this);
        fillItem.addItemListener(this);
        noFillItem.addItemListener(this);
        blackLineItem.addItemListener(this);
        redLineItem.addItemListener(this);          
        orangeLineItem.addItemListener(this);
        yellowLineItem.addItemListener(this);
        greenLineItem.addItemListener(this);
        blueLineItem.addItemListener(this);
        purpleLineItem.addItemListener(this);
        grayLineItem.addItemListener(this);
        oneItem.addItemListener(this);
        twoItem.addItemListener(this);
        threeItem.addItemListener(this);
        fourItem.addItemListener(this);
        fiveItem.addItemListener(this);     

        drawingpanel = new Panel();
        drawingpanel.setLayout(null);
        drawingpanel.setSize(800,600);
        drawingpanel.addMouseListener(this);
        drawingpanel.addMouseMotionListener(this);
        setBounds(100,100,800,600);
        setLayout(new BorderLayout());

        add("Center",drawingpanel);
        addWindowListener(this);
        setResizable(true);
        pack();
        setVisible(true);
        thread.start();
    }

    public static void main(String [] args)
    {
        new E3G04();
    }
    public void run()
    {       
        obj = getGraphics();
        System.out.print("here");
        obj.setColor(Color.black);
        obj.drawRect(200,200,100,100);
        obj.fillRect(200,200,100,100);
        while(running)
        {           
            //other stuff to come
        }
    }

    public void stop()
    {
        drawingpanel.removeMouseListener(this);
        newItem.removeActionListener(this);
        quitItem.removeActionListener(this);
        ovalItem.removeItemListener(this);
        rectItem.removeItemListener(this);
        lineItem.removeItemListener(this);
        fillItem.removeItemListener(this);
        noFillItem.removeItemListener(this);
        blackLineItem.removeItemListener(this);
        redLineItem.removeItemListener(this);           
        orangeLineItem.removeItemListener(this);
        yellowLineItem.removeItemListener(this);
        greenLineItem.removeItemListener(this);
        blueLineItem.removeItemListener(this);
        purpleLineItem.removeItemListener(this);
        grayLineItem.removeItemListener(this);
        oneItem.removeItemListener(this);
        twoItem.removeItemListener(this);
        threeItem.removeItemListener(this);
        fourItem.removeItemListener(this);
        fiveItem.removeItemListener(this);  
        dispose();
        System.exit(0);
    }

    public void disableFillColor()
    {
        colorMenu.removeAll();
        colorMenu.add(blackLineItem);
        colorMenu.add(redLineItem);
        colorMenu.add(orangeLineItem);
        colorMenu.add(yellowLineItem);
        colorMenu.add(greenLineItem);
        colorMenu.add(blueLineItem);
        colorMenu.add(purpleLineItem);
        colorMenu.add(grayLineItem);
    }
    public void enableAllColors()
    {
        colorMenu.removeAll();
        colorMenu.add(blackLineItem);
        colorMenu.add(redLineItem);
        colorMenu.add(orangeLineItem);
        colorMenu.add(yellowLineItem);
        colorMenu.add(greenLineItem);
        colorMenu.add(blueLineItem);
        colorMenu.add(purpleLineItem);
        colorMenu.add(grayLineItem);        
        colorMenu.addSeparator();
        colorMenu.add(blackFillItem);
        colorMenu.add(redFillItem);
        colorMenu.add(orangeFillItem);
        colorMenu.add(yellowFillItem);
        colorMenu.add(greenFillItem);
        colorMenu.add(blueFillItem);
        colorMenu.add(purpleFillItem);
        colorMenu.add(grayFillItem);
    }
    public void actionPerformed(ActionEvent e)
    {
        Object o = e.getSource();

        if (o == newItem)
        {
            //Clear Screen
        }

        if (o == quitItem)
        {   
            thread.stop();
            running = false;
            stop();
        }
    }      

    public void mouseClicked(MouseEvent m)
    {
        Object o = m.getSource();
    }   

    public void mousePressed(MouseEvent m)
    {
        start = m.getPoint();
        end = start;
        cur = start;
    }

    public void mouseDragged(MouseEvent m)
    {
        cur = m.getPoint();
    }   

    public void mouseReleased(MouseEvent m)
    {
        end = cur;
    }   

    public void itemStateChanged(ItemEvent e)
    {
        //Code removed for brevity
    }
    public void windowClosing(WindowEvent e)
    {
        running = false;
        stop();
    }
    public void mouseExited(MouseEvent m)
    {}
    public void mouseEntered(MouseEvent m)
    {}  
    public void mouseMoved(MouseEvent m)
    { }
    public void windowClosed(WindowEvent e){}
    public void windowOpened(WindowEvent e){}
    public void windowActivated(WindowEvent e){}
    public void windowDeactivated(WindowEvent e){}
    public void windowIconified(WindowEvent e){}
    public void windowDeiconified(WindowEvent e){}
}

Answer 1

1. Never maintain a reference to the Graphics context. The Graphics context is stateless (that is, it's state is reset between paint cycles), it also possible for the Graphics context to change between paint cycles, leaving you with a invalid context.

Answer 2

In an AWT application, whenever you want to draw, you generally create a subclass of Canvas overriding the paint(Graphics) method. See Java AWT Canvas – Freelance Drawing for an example.

The reason why your current approach is not working is unfortunately very complex. All drawing must be done on an event dispatch thread (also called AWT thread), for example. AWT creates these special threads for you, and for the most part, you do not need to worry about it except when creating your own threads. Also, as MadProgrammer pointed out, you should not hold onto Graphics references. You should only use a Graphics reference provided to you by AWT for the duration of the method. One exception to this is a Graphics reference obtained from BufferedImages (a so-called software graphics context).