How do I convert this Applet to launch from a JFrame instead??

Question

   A simple program where the user can sketch curves and shapes in a
   variety of colors on a variety of background colors.  The user selects
   a drawing color form a pop-up menu at the top of the
   applet.  If the user clicks "Set Background", the background
   color is set to the current drawing color and the drawing
   area is filled with that color.  If the user clicks "Clear",
   the drawing area is just filled with the current background color.
   The user selects the shape to draw from another pop-up menu at the
   top of the applet.  The user can draw free-hand curves, straight
   lines, and one of six different types of shapes.
   The user's drawing is saved in an off-screen image, which is
   used to refresh the screen when repainting.  The picture is
   lost if the applet changes size, however.
   This file defines two classes, SimplePaint3,class, and
   class, SimplePaint3$Display.class.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class SimplePaint3 extends JApplet {
        // The main applet class simply sets up the applet.  Most of the
        // work is done in the Display class.
   JComboBox colorChoice, figureChoice;  // Pop-up menus, defined as instance
                                         // variables so that the Display
                                         // class can see them.
   public void init() {
      setBackground(Color.gray);
      getContentPane().setBackground(Color.gray);
      Display canvas = new Display();  // The drawing area.
      getContentPane().add(canvas,BorderLayout.CENTER);
      JPanel buttonBar = new JPanel();       // A panel to hold the buttons.
      buttonBar.setBackground(Color.gray);
      getContentPane().add(buttonBar, BorderLayout.SOUTH);
      JPanel choiceBar = new JPanel();       // A panel to hole the pop-up menus
      choiceBar.setBackground(Color.gray);
      getContentPane().add(choiceBar, BorderLayout.NORTH);
      JButton fill = new JButton("Set Background");  // The first button.
      fill.addActionListener(canvas);
      buttonBar.add(fill);
      JButton clear = new JButton("Clear");   // The second button.
      clear.addActionListener(canvas);
      buttonBar.add(clear);
      colorChoice = new JComboBox();  // The pop-up menu of colors.
      colorChoice.addItem("Black");
      colorChoice.addItem("Red");
      colorChoice.addItem("Green");
      colorChoice.addItem("Blue");
      colorChoice.addItem("Cyan");
      colorChoice.addItem("Magenta");
      colorChoice.addItem("Yellow");
      colorChoice.addItem("White");
      colorChoice.setBackground(Color.white);
      choiceBar.add(colorChoice);
      figureChoice = new JComboBox();  // The pop-up menu of shapes.
      figureChoice.addItem("Curve");
      figureChoice.addItem("Straight Line");
      figureChoice.addItem("Rectangle");
      figureChoice.addItem("Oval");
      figureChoice.addItem("RoundRect");
      figureChoice.addItem("Filled Rectangle");
      figureChoice.addItem("Filled Oval");
      figureChoice.addItem("Filled RoundRect");
      figureChoice.setBackground(Color.white);
      choiceBar.add(figureChoice);
   }  // end init()
   public Insets getInsets() {
          // Specify how wide a border to leave around the edges of the applet.
      return new Insets(3,3,3,3);
   private class Display extends JPanel
              implements MouseListener, MouseMotionListener, ActionListener {
           // Nested class Display represents the drawing surface of the
           // applet.  It lets the user use the mouse to draw colored curves
           // and shapes.  The current color is specified by the pop-up menu
           // colorChoice.  The current shape is specified by another pop-up menu,
           // figureChoice.  (These are instance variables in the main class.)
           // The panel also listens for action events from buttons
           // named "Clear" and "Set Background".  The "Clear" button fills
           // the panel with the current background color.  The "Set Background"
           // button sets the background color to the current drawing color and
           // then clears.  These buttons are set up in the main class.
      private final static int
                  BLACK = 0,
                  RED = 1,            // Some constants to make
                  GREEN = 2,          // the code more readable.
                  BLUE = 3,           // These numbers code for
                  CYAN = 4,           // the different drawing colors.
                  MAGENTA = 5,
                  YELLOW = 6,
                  WHITE = 7;
      private final static int
                 CURVE = 0,
                 LINE = 1,
                 RECT = 2,               // Some constants that code
                 OVAL = 3,               // for the different types of
                 ROUNDRECT = 4,          // figure the program can draw.
                 FILLED_RECT = 5,
                 FILLED_OVAL = 6,
                 FILLED_ROUNDRECT = 7;
      /* Some variables used for backing up the contents of the panel. */
      Image OSI;  // The off-screen image (created in checkOSI()).
      int widthOfOSI, heightOfOSI;  // Current width and height of OSI.  These
                                    // are checked against the size of the applet,
                                    // to detect any change in the panel's size.
                                    // If the size has changed, a new OSI is created.
                                    // The picture in the off-screen image is lost
                                    // when that happens.
      /* The following variables are used when the user is sketching a
         curve while dragging a mouse. */
      private int mouseX, mouseY;   // The location of the mouse.
      private int prevX, prevY;     // The previous location of the mouse.
      private int startX, startY;   // The starting position of the mouse.
                                    // (Not used for drawing curves.)
      private boolean dragging;     // This is set to true when the user is drawing.
      private int figure;    // What type of figure is being drawn.  This is
                             //    specified by the figureChoice menu.
      private Graphics dragGraphics;  // A graphics context for the off-screen image,
                                      // to be used while a drag is in progress.
      private Color dragColor;  // The color that is used for the figure that is
                                // being drawn.
      Display() {
             // Constructor.  When this component is first created, it is set to
             // listen for mouse events and mouse motion events from
             // itself.  The initial background color is white.
         addMouseListener(this);
         addMouseMotionListener(this);
         setBackground(Color.white);
      private void drawFigure(Graphics g, int shape, int x1, int y1, int x2, int y2) {
            // This method is called to do ALL drawing in this applet!
            // Draws a shape in the graphics context g.
            // The shape paramter tells what kind of shape to draw.  This
            // can be LINE, RECT, OVAL, ROUNTRECT, FILLED_RECT,
            // FILLED_OVAL, or FILLED_ROUNDRECT.  (Note that a CURVE is
            // drawn by drawing multiple LINES, so the shape parameter is
            // never equal to CURVE.)  For a LINE, a line is drawn from
            // the point (x1,y1) to (x2,y2).  For other shapes,  the
            // points (x1,y1) and (x2,y2) give two corners of the shape
            // (or of a rectangle that contains the shape).
         if (shape == LINE) {
               // For a line, just draw the line between the two points.
            g.drawLine(x1,y1,x2,y2);
            return;
         int x, y;  // Top left corner of rectangle that contains the figure.
         int w, h;  // Width and height of rectangle that contains the figure.
         if (x1 >= x2) {  // x2 is left edge
            x = x2;
            w = x1 - x2;
         else {          // x1 is left edge
            x = x1;
            w = x2 - x1;
         if (y1 >= y2) {  // y2 is top edge
            y = y2;
            h = y1 - y2;
         else {          // y1 is top edge.
            y = y1;
            h = y2 - y1;
         switch (shape) {   // Draw the appropriate figure.
            case RECT:
               g.drawRect(x, y, w, h);
               break;
            case OVAL:
               g.drawOval(x, y, w, h);
               break;
            case ROUNDRECT:
               g.drawRoundRect(x, y, w, h, 20, 20);
               break;
            case FILLED_RECT:
               g.fillRect(x, y, w, h);
               break;
            case FILLED_OVAL:
               g.fillOval(x, y, w, h);
               break;
            case FILLED_ROUNDRECT:
               g.fillRoundRect(x, y, w, h, 20, 20);
               break;
      private void repaintRect(int x1, int y1, int x2, int y2) {
            // Call repaint on a rectangle that contains the points (x1,y1)
            // and (x2,y2).  (Add a 1-pixel border along right and bottom
            // edges to allow for the pen overhang when drawing a line.)
         int x, y;  // top left corner of rectangle that contains the figure
         int w, h;  // width and height of rectangle that contains the figure
         if (x2 >= x1) {  // x1 is left edge
            x = x1;
            w = x2 - x1;
         else {          // x2 is left edge
            x = x2;
            w = x1 - x2;
         if (y2 >= y1) {  // y1 is top edge
            y = y1;
            h = y2 - y1;
         else {          // y2 is top edge.
            y = y2;
            h = y1 - y2;
         repaint(x,y,w+1,h+1);
      private void checkOSI() {
           // This method is responsible for creating the off-screen image.
           // It should be called before using the OSI.  It will make a new OSI if
           // the size of the panel changes.
         if (OSI == null || widthOfOSI != getSize().width || heightOfOSI != getSize().height) {
                // Create the OSI, or make a new one if panel size has changed.
            OSI = null;  // (If OSI already exists, this frees up the memory.)
            OSI = createImage(getSize().width, getSize().height);
            widthOfOSI = getSize().width;
            heightOfOSI = getSize().height;
            Graphics OSG = OSI.getGraphics();  // Graphics context for drawing to OSI.
            OSG.setColor(getBackground());
            OSG.fillRect(0, 0, widthOfOSI, heightOfOSI);
            OSG.dispose();
      public void paintComponent(Graphics g) {
           // Copy the off-screen image to the screen,
           // after checking to make sure it exists.  Then,
           // if a shape other than CURVE is being drawn,
           // draw it on top of the image from the OSI.
         checkOSI();
         g.drawImage(OSI, 0, 0, this);
         if (dragging && figure != CURVE) {
            g.setColor(dragColor);
            drawFigure(g,figure,startX,startY,mouseX,mouseY);
      public void actionPerformed(ActionEvent evt) {
              // Respond when the user clicks on a button.  The
              // command must be either "Clear" or "Set Background".
         String command = evt.getActionCommand();
         checkOSI();
         if (command.equals("Set Background")) {
                // Set background color before clearing.
                // Change the selected color so it is different
                // from the background color.
            setBackground(getCurrentColor());
            if (colorChoice.getSelectedIndex() == BLACK)
               colorChoice.setSelectedIndex(WHITE);
            else
               colorChoice.setSelectedIndex(BLACK);
         Graphics g = OSI.getGraphics();
         g.setColor(getBackground());
         g.fillRect(0,0,getSize().width,getSize().height);
         g.dispose();
         repaint();
      private Color getCurrentColor() {
               // Check the colorChoice menu to find the currently
               // selected color, and return the appropriate color
               // object.
         int currentColor = colorChoice.getSelectedIndex();
         switch (currentColor) {
            case BLACK:
               return Color.black;
            case RED:
               return Color.red;
            case GREEN:
               return Color.green;
            case BLUE:
               return Color.blue;
            case CYAN:
               return Color.cyan;
            case MAGENTA:
               return Color.magenta;
            case YELLOW:
               return Color.yellow;
            default:
               return Color.white;
      public void mousePressed(MouseEvent evt) {
              // This is called when the user presses the mouse on the
              // panel.  This begins a draw operation in which the user
              // sketches a curve or draws a shape.  (Note that curves
              // are handled differently from other shapes.  For CURVE,
              // a new segment of the curve is drawn each time the user
              // moves the mouse.  For the other shapes, a "rubber band
              // cursor" is used.  That is, the figure is drawn between
              // the starting point and the current mouse location.)
         if (dragging == true)  // Ignore mouse presses that occur
             return;            //    when user is already drawing a curve.
                                //    (This can happen if the user presses
                                //    two mouse buttons at the same time.)
         prevX = startX = evt.getX();  // Save mouse coordinates.
         prevY = startY = evt.getY();
         figure = figureChoice.getSelectedIndex();
         dragColor = getCurrentColor();        
         dragGraphics = OSI.getGraphics();
         dragGraphics.setColor(dragColor);
         dragging = true;  // Start drawing.
      } // end mousePressed()
      public void mouseReleased(MouseEvent evt) {
              // Called whenever the user releases the mouse button.
              // If the user was drawing a shape, we make the shape
              // permanent by drawing it to the off-screen image.
          if (dragging == false)
             return;  // Nothing to do because the user isn't drawing.
          dragging = false;
          mouseX = evt.getX();
          mouseY = evt.getY();
          if (figure == CURVE) {
                 // A CURVE is drawn as a series of LINEs
              drawFigure(dragGraphics,LINE,prevX,prevY,mouseX,mouseY);
              repaintRect(prevX,prevY,mouseX,mouseY);
          else if (figure == LINE) {
             repaintRect(startX,startY,prevX,prevY);
             if (mouseX != startX || mouseY != startY) {
                   // Draw the line only if it has non-zero length.
                drawFigure(dragGraphics,figure,startX,startY,mouseX,mouseY);
                repaintRect(startX,startY,mouseX,mouseY);
          else {
             repaintRect(startX,startY,prevX,prevY);
             if (mouseX != startX && mouseY != startY) {
                   // Draw the shape only if both its height
                   // and width are both non-zero.
                drawFigure(dragGraphics,figure,startX,startY,mouseX,mouseY);
                repaintRect(startX,startY,mouseX,mouseY);
          dragGraphics.dispose();
          dragGraphics = null;
      public void mouseDragged(MouseEvent evt) {
               // Called whenever the user moves the mouse while a mouse button
               // is down.  If the user is drawing a curve, draw a segment of
               // the curve on the off-screen image, and repaint the part
               // of the panel that contains the new line segment.  Otherwise,
               // just call repaint and let paintComponent() draw the shape on
               // top of the picture in the off-screen image.
          if (dragging == false)
             return;  // Nothing to do because the user isn't drawing.
          mouseX = evt.getX();   // x-coordinate of mouse.
          mouseY = evt.getY();   // y=coordinate of mouse.
          if (figure == CURVE) {
                 // A CURVE is drawn as a series of LINEs.
             drawFigure(dragGraphics,LINE,prevX,prevY,mouseX,mouseY);
             repaintRect(prevX,prevY,mouseX,mouseY);
          else {
                // Repaint two rectangles:  The one that contains the previous
                // version of the figure, and the one that will contain the
                // new version.  The first repaint is necessary to restore
                // the picture from the off-screen image in that rectangle.
             repaintRect(startX,startY,prevX,prevY);
             repaintRect(startX,startY,mouseX,mouseY);
          prevX = mouseX;  // Save coords for the next call to mouseDragged or mouseReleased.
          prevY = mouseY;
      } // end mouseDragged.
      public void mouseEntered(MouseEvent evt) { }   // Some empty routines.
      public void mouseExited(MouseEvent evt) { }    //    (Required by the MouseListener
      public void mouseClicked(MouseEvent evt) { }   //    and MouseMotionListener
      public void mouseMoved(MouseEvent evt) { }     //    interfaces).
   } // end nested class Display
} // end class SimplePaint3

Answer 1

Im quite the novice, how exactly do I go about doing that. What I did was to put both in diff files but I got errors saying that they cant find colorChoice, figureChoice in the Display class.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Simple extends JFrame implements Display{
        // The main applet class simply sets up the applet.  Most of the
        // work is done in the Display class.
   JComboBox colorChoice, figureChoice;  // Pop-up menus, defined as instance
                                         // variables so that the Display
                                         // class can see them.
   public void init() {
      setBackground(Color.gray);
      getContentPane().setBackground(Color.gray);
      Display canvas = new Display();  // The drawing area.
      getContentPane().add(canvas,BorderLayout.CENTER);
      JPanel buttonBar = new JPanel();       // A panel to hold the buttons.
      buttonBar.setBackground(Color.gray);
      getContentPane().add(buttonBar, BorderLayout.SOUTH);
      JPanel choiceBar = new JPanel();       // A panel to hole the pop-up menus
      choiceBar.setBackground(Color.gray);
      getContentPane().add(choiceBar, BorderLayout.NORTH);
      JButton fill = new JButton("Set Background");  // The first button.
      fill.addActionListener(canvas);
      buttonBar.add(fill);
      JButton clear = new JButton("Clear");   // The second button.
      clear.addActionListener(canvas);
      buttonBar.add(clear);
      colorChoice = new JComboBox();  // The pop-up menu of colors.
      colorChoice.addItem("Black");
      colorChoice.addItem("Red");
      colorChoice.addItem("Green");
      colorChoice.addItem("Blue");
      colorChoice.addItem("Cyan");
      colorChoice.addItem("Magenta");
      colorChoice.addItem("Yellow");
      colorChoice.addItem("White");
      colorChoice.setBackground(Color.white);
      choiceBar.add(colorChoice);
      figureChoice = new JComboBox();  // The pop-up menu of shapes.
      figureChoice.addItem("Curve");
      figureChoice.addItem("Straight Line");
      figureChoice.addItem("Rectangle");
      figureChoice.addItem("Oval");
      figureChoice.addItem("RoundRect");
      figureChoice.addItem("Filled Rectangle");
      figureChoice.addItem("Filled Oval");
      figureChoice.addItem("Filled RoundRect");
      figureChoice.setBackground(Color.white);
      choiceBar.add(figureChoice);
   }  // end init()
} // end class SimplePaint3
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class Display extends JPanel
              implements MouseListener, MouseMotionListener, ActionListener {
           // Nested class Display represents the drawing surface of the
           // applet.  It lets the user use the mouse to draw colored curves
           // and shapes.  The current color is specified by the pop-up menu
           // colorChoice.  The current shape is specified by another pop-up menu,
           // figureChoice.  (These are instance variables in the main class.)
           // The panel also listens for action events from buttons
           // named "Clear" and "Set Background".  The "Clear" button fills
           // the panel with the current background color.  The "Set Background"
           // button sets the background color to the current drawing color and
           // then clears.  These buttons are set up in the main class.
      private final static int
                  BLACK = 0,
                  RED = 1,            // Some constants to make
                  GREEN = 2,          // the code more readable.
                  BLUE = 3,           // These numbers code for
                  CYAN = 4,           // the different drawing colors.
                  MAGENTA = 5,
                  YELLOW = 6,
                  WHITE = 7;
      private final static int
                 CURVE = 0,
                 LINE = 1,
                 RECT = 2,               // Some constants that code
                 OVAL = 3,               // for the different types of
                 ROUNDRECT = 4,          // figure the program can draw.
                 FILLED_RECT = 5,
                 FILLED_OVAL = 6,
                 FILLED_ROUNDRECT = 7;
      /* Some variables used for backing up the contents of the panel. */
      Image OSI;  // The off-screen image (created in checkOSI()).
      int widthOfOSI, heightOfOSI;  // Current width and height of OSI.  These
                                    // are checked against the size of the applet,
                                    // to detect any change in the panel's size.
                                    // If the size has changed, a new OSI is created.
                                    // The picture in the off-screen image is lost
                                    // when that happens.
      /* The following variables are used when the user is sketching a
         curve while dragging a mouse. */
      private int mouseX, mouseY;   // The location of the mouse.
      private int prevX, prevY;     // The previous location of the mouse.
      private int startX, startY;   // The starting position of the mouse.
                                    // (Not used for drawing curves.)
      private boolean dragging;     // This is set to true when the user is drawing.
      private int figure;    // What type of figure is being drawn.  This is
                             //    specified by the figureChoice menu.
      private Graphics dragGraphics;  // A graphics context for the off-screen image,
                                      // to be used while a drag is in progress.
      private Color dragColor;  // The color that is used for the figure that is
                                // being drawn.
      Display() {
             // Constructor.  When this component is first created, it is set to
             // listen for mouse events and mouse motion events from
             // itself.  The initial background color is white.
         addMouseListener(this);
         addMouseMotionListener(this);
         setBackground(Color.white);
      private void drawFigure(Graphics g, int shape, int x1, int y1, int x2, int y2) {
            // This method is called to do ALL drawing in this applet!
            // Draws a shape in the graphics context g.
            // The shape paramter tells what kind of shape to draw.  This
            // can be LINE, RECT, OVAL, ROUNTRECT, FILLED_RECT,
            // FILLED_OVAL, or FILLED_ROUNDRECT.  (Note that a CURVE is
            // drawn by drawing multiple LINES, so the shape parameter is
            // never equal to CURVE.)  For a LINE, a line is drawn from
            // the point (x1,y1) to (x2,y2).  For other shapes,  the
            // points (x1,y1) and (x2,y2) give two corners of the shape
            // (or of a rectangle that contains the shape).
         if (shape == LINE) {
               // For a line, just draw the line between the two points.
            g.drawLine(x1,y1,x2,y2);
            return;
         int x, y;  // Top left corner of rectangle that contains the figure.
         int w, h;  // Width and height of rectangle that contains the figure.
         if (x1 >= x2) {  // x2 is left edge
            x = x2;
            w = x1 - x2;
         else {          // x1 is left edge
            x = x1;
            w = x2 - x1;
         if (y1 >= y2) {  // y2 is top edge
            y = y2;
            h = y1 - y2;
         else {          // y1 is top edge.
            y = y1;
            h = y2 - y1;
         switch (shape) {   // Draw the appropriate figure.
            case RECT:
               g.drawRect(x, y, w, h);
               break;
            case OVAL:
               g.drawOval(x, y, w, h);
               break;
            case ROUNDRECT:
               g.drawRoundRect(x, y, w, h, 20, 20);
               break;
            case FILLED_RECT:
               g.fillRect(x, y, w, h);
               break;
            case FILLED_OVAL:
               g.fillOval(x, y, w, h);
               break;
            case FILLED_ROUNDRECT:
               g.fillRoundRect(x, y, w, h, 20, 20);
               break;
      private void repaintRect(int x1, int y1, int x2, int y2) {
            // Call repaint on a rectangle that contains the points (x1,y1)
            // and (x2,y2).  (Add a 1-pixel border along right and bottom
            // edges to allow for the pen overhang when drawing a line.)
         int x, y;  // top left corner of rectangle that contains the figure
         int w, h;  // width and height of rectangle that contains the figure
         if (x2 >= x1) {  // x1 is left edge
            x = x1;
            w = x2 - x1;
         else {          // x2 is left edge
            x = x2;
            w = x1 - x2;
         if (y2 >= y1) {  // y1 is top edge
            y = y1;
            h = y2 - y1;
         else {          // y2 is top edge.
            y = y2;
            h = y1 - y2;
         repaint(x,y,w+1,h+1);
      private void checkOSI() {
           // This method is responsible for creating the off-screen image.
           // It should be called before using the OSI.  It will make a new OSI if
           // the size of the panel changes.
         if (OSI == null || widthOfOSI != getSize().width || heightOfOSI != getSize().height) {
                // Create the OSI, or make a new one if panel size has changed.
            OSI = null;  // (If OSI already exists, this frees up the memory.)
            OSI = createImage(getSize().width, getSize().height);
            widthOfOSI = getSize().width;
            heightOfOSI = getSize().height;
            Graphics OSG = OSI.getGraphics();  // Graphics context for drawing to OSI.
            OSG.setColor(getBackground());
            OSG.fillRect(0, 0, widthOfOSI, heightOfOSI);
            OSG.dispose();
      public void paintComponent(Graphics g) {
           // Copy the off-screen image to the screen,
           // after checking to make sure it exists.  Then,
           // if a shape other than CURVE is being drawn,
           // draw it on top of the image from the OSI.
         checkOSI();
         g.drawImage(OSI, 0, 0, this);
         if (dragging && figure != CURVE) {
            g.setColor(dragColor);
            drawFigure(g,figure,startX,startY,mouseX,mouseY);
      public void actionPerformed(ActionEvent evt) {
              // Respond when the user clicks on a button.  The
              // command must be either "Clear" or "Set Background".
         String command = evt.getActionCommand();
         checkOSI();
         if (command.equals("Set Background")) {
                // Set background color before clearing.
                // Change the selected color so it is different
                // from the background color.
            setBackground(getCurrentColor());
            if (colorChoice.getSelectedIndex() == BLACK)
               colorChoice.setSelectedIndex(WHITE);
            else
               colorChoice.setSelectedIndex(BLACK);
         Graphics g = OSI.getGraphics();
         g.setColor(getBackground());
         g.fillRect(0,0,getSize().width,getSize().height);
         g.dispose();
         repaint();
      private Color getCurrentColor() {
               // Check the colorChoice menu to find the currently
               // selected color, and return the appropriate color
               // object.
         int currentColor = colorChoice.getSelectedIndex();
         switch (currentColor) {
            case BLACK:
               return Color.black;
            case RED:
               return Color.red;
            case GREEN:
               return Color.green;
            case BLUE:
               return Color.blue;
            case CYAN:
               return Color.cyan;
            case MAGENTA:
               return Color.magenta;
            case YELLOW:
               return Color.yellow;
            default:
               return Color.white;
      public void mousePressed(MouseEvent evt) {
              // This is called when the user presses the mouse on the
              // panel.  This begins a draw operation in which the user
              // sketches a curve or draws a shape.  (Note that curves
              // are handled differently from other shapes.  For CURVE,
              // a new segment of the curve is drawn each time the user
              // moves the mouse.  For the other shapes, a "rubber band
              // cursor" is used.  That is, the figure is drawn between
              // the starting point and the current mouse location.)
         if (dragging == true)  // Ignore mouse presses that occur
             return;            //    when user is already drawing a curve.
                                //    (This can happen if the user presses
                                //    two mouse buttons at the same time.)
         prevX = startX = evt.getX();  // Save mouse coordinates.
         prevY = startY = evt.getY();
         figure = figureChoice.getSelectedIndex();
         dragColor = getCurrentColor();        
         dragGraphics = OSI.getGraphics();
         dragGraphics.setColor(dragColor);
         dragging = true;  // Start drawing.
      } // end mousePressed()
      public void mouseReleased(MouseEvent evt) {
              // Called whenever the user releases the mouse button.
              // If the user was drawing a shape, we make the shape
              // permanent by drawing it to the off-screen image.
          if (dragging == false)
             return;  // Nothing to do because the user isn't drawing.
          dragging = false;
          mouseX = evt.getX();
          mouseY = evt.getY();
          if (figure == CURVE) {
                 // A CURVE is drawn as a series of LINEs
              drawFigure(dragGraphics,LINE,prevX,prevY,mouseX,mouseY);
              repaintRect(prevX,prevY,mouseX,mouseY);
          else if (figure == LINE) {
             repaintRect(startX,startY,prevX,prevY);
             if (mouseX != startX || mouseY != startY) {
                   // Draw the line only if it has non-zero length.
                drawFigure(dragGraphics,figure,startX,startY,mouseX,mouseY);
                repaintRect(startX,startY,mouseX,mouseY);
          else {
             repaintRect(startX,startY,prevX,prevY);
             if (mouseX != startX && mouseY != startY) {
                   // Draw the shape only if both its height
                   // and width are both non-zero.
                drawFigure(dragGraphics,figure,startX,startY,mouseX,mouseY);
                repaintRect(startX,startY,mouseX,mouseY);
          dragGraphics.dispose();
          dragGraphics = null;
      public void mouseDragged(MouseEvent evt) {
               // Called whenever the user moves the mouse while a mouse button
               // is down.  If the user is drawing a curve, draw a segment of
               // the curve on the off-screen image, and repaint the part
               // of the panel that contains the new line segment.  Otherwise,
               // just call repaint and let paintComponent() draw the shape on
               // top of the picture in the off-screen image.
          if (dragging == false)
             return;  // Nothing to do because the user isn't drawing.
          mouseX = evt.getX();   // x-coordinate of mouse.
          mouseY = evt.getY();   // y=coordinate of mouse.
          if (figure == CURVE) {
                 // A CURVE is drawn as a series of LINEs.
             drawFigure(dragGraphics,LINE,prevX,prevY,mouseX,mouseY);
             repaintRect(prevX,prevY,mouseX,mouseY);
          else {
                // Repaint two rectangles:  The one that contains the previous
                // version of the figure, and the one that will contain the
                // new version.  The first repaint is necessary to restore
                // the picture from the off-screen image in that rectangle.
             repaintRect(startX,startY,prevX,prevY);
             repaintRect(startX,startY,mouseX,mouseY);
          prevX = mouseX;  // Save coords for the next call to mouseDragged or mouseReleased.
          prevY = mouseY;
      } // end mouseDragged.
      public void mouseEntered(MouseEvent evt) { }   // Some empty routines.
      public void mouseExited(MouseEvent evt) { }    //    (Required by the MouseListener
      public void mouseClicked(MouseEvent evt) { }   //    and MouseMotionListener
      public void mouseMoved(MouseEvent evt) { }     //    interfaces).
   } // end nested class Display