Graphics2D - why doesn't this draw?

I'm trying to convert a simple Turtle Graphics applet to Graphics2D - it draws lines on the applet at different angles and in different colours.  It compiles and runs but doesn't draw anything.  I've cut out a lot of the functions for clarity - can anyone tell mewhy this doesn't draw?

class Turtle extends JPanel {
     Graphics2D g2;
     Vector linesToDraw = new Vector();
     private int vectorCount = 0;
     private Color penColour = Color.black;
     private Color background = Color.cyan;
     public int heading = -90;
     public int size = 50;
       public float currentX = 0, currentY = 0, newX, newY;       public boolean penIsDown = true;
       
  /**Construct the application*/
       public Turtle() {
         //home();
       }

       //returns current heading of turtle
       public final int getHeading() {
         return heading;
       }
       
       //moves forward by length
       public final void forward(int length) {
         newX+=(length)*Math.cos(Math.PI*getHeading()/180.0);
         newY+=(length)*Math.sin(Math.PI*getHeading()/180.0);
         //draw new line based on coordinates and colours
         line((int)currentX, (int)currentY, (int)newX, (int)newY, penColour, background, penIsDown);
          //set X and Y coordinates for next move
         currentX = newX;
         currentY = newY;
         //repaint the screen
         repaint();
      }

       public void paintComponent(Graphics2D g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g;
          forward(100);
       }
             
       public final void line(int x1, int y1, int x2, int y2, Color c, Color b, boolean penDown) {
            Draw d = new Draw();
            d.setStartPoint(x1, y1);
            d.setEndPoint(x2, y2);
            d.setPenColour(Color.black);
            d.setBackground(b);
            d.setPenStatus(true);
            linesToDraw.addElement(d);
            vectorCount++;
            d.drawNewLine(g2);
       }
     
      class Draw {
           private int x1, x2, y1, y2;
           private boolean penDown;
           private Color b, c;
           
           public final void setStartPoint(int x, int y) {
                x1 = x;
                y1 = y;
           }
           
           public final void setEndPoint(int x, int y) {
                x2 = x;
                y2 = y;
           }
           
           public final void setPenStatus(boolean pD) {
                penDown = pD;
           }
           
           public final void setPenColour (Color C) {
                c = C;
           }
           
           public final void setBackground(Color B) {
                b = B;
           }
           
           public final void drawNewLine(Graphics2D g) {
                g.setColor(c);
                setBackground(b);
                if (penDown) g.draw(new Line2D.Double(x1, x2, y1, y2));
           }
      }
 
    public static void main(String args[]) {
      }
     
}