[Beginner] Moving a simple Shape

Question

Hi all !
I need to write a simple application which draws basic shapes and let the user drag this shapes.
I have found a sample code which does this with gif images rendered inside JLabels and adapted to use shapes (in this case a Ellipse2D) but nothing is drawn on the screen.
Why ?
Can anybody give me a help to fix it ?
Thanks
Francesco
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Ellipse2D;
import java.awt.image.BufferedImage;
public class Main implements MouseMotionListener {
     JFrame frame;
     JLabel img;
     private final Graphics2D offscreen;
     public Main() {
          frame = new JFrame("test");
          frame.getContentPane().setLayout(null);
          frame.setBounds(0, 0, 500, 400);
          BufferedImage offscreenImage = new BufferedImage(200, 200,
                    BufferedImage.TYPE_INT_RGB);
          offscreen = offscreenImage.createGraphics();
          offscreen.setColor(Color.BLACK);
          offscreen.draw(new Ellipse2D.Double(10, 10, 120, 120));
          ImageIcon icon = new ImageIcon(offscreenImage);
          JLabel draw = new JLabel(icon);
          draw.addMouseMotionListener(this);
          frame.getContentPane().add(draw);
          frame.setVisible(true);
     public void mouseMoved(MouseEvent e) {
     public void mouseDragged(MouseEvent e) {
          img.setBounds(img.getX() + e.getX() - 10, img.getY() + e.getY() - 10,
                    36, 39);
     public static void main(String args[]) {
          new Main();
}

Answer 1

(1) When you use null layout you need to setBounds for each component, since there is no LayoutManager to take care of sizing and placement.
(2) A newly constructed BufferedImage is filled with black pixels and drawing in black wouldn't show anyhow.
Considering these two points, I've reworked your code... I renamed the reference variables as I find it inconvenient to have to remember that offscreen is in fact a Graphics2D object, and img is a JLabel. For future postings here, I strongly suggest that you name your variables after the class they represent... doing this will surely get you faster and better responses.import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Ellipse2D;
import java.awt.image.BufferedImage;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
public class Main implements MouseMotionListener {
    JFrame frame;
    JLabel label;
    private final Graphics2D graphics2D;
    public Main () {
        frame = new JFrame ("test");
        frame.getContentPane ().setLayout (null);
        frame.setBounds (0, 0, 500, 400);
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        BufferedImage bufferedImage =
                new BufferedImage (200, 200, BufferedImage.TYPE_INT_RGB);
        graphics2D = bufferedImage.createGraphics ();
        graphics2D.setColor (Color.RED); // changed
        graphics2D.draw (new Ellipse2D.Double (50, 50, 100, 100));
        ImageIcon imageIcon = new ImageIcon (bufferedImage);
        label = new JLabel (imageIcon);
        label.setBounds (0, 0, 104, 104); // added
        label.addMouseMotionListener (this);
        frame.getContentPane ().add (label);
        frame.setVisible (true);
    public void mouseMoved (MouseEvent e) { }
    public void mouseDragged (MouseEvent e) {
        label.setBounds (label.getX () + e.getX () - 10,
                label.getY () + e.getY () - 10,
                label.getWidth (), label.getHeight ());
    public static void main (String args[]) {
        new Main ();
}You might want to use a MouseAdapter or add a MouseListener to capture the coordinates of mousePressed and use them as an offset for a more intuitive drag effect.
Cheers, Darryl
PS -- I'm not really into Graphics work, just trying to learn something new -- could you or somebody tell me why the Ellipse2D constructor doesn't seem to behave as per the documentation?
public Ellipse2D.Double(double x, double y, double w, double h)
Constructs and initializes an Ellipse2D from the specified coordinates.
Parameters:
x - the X coordinate of the upper-left corner of the framing rectangle
y - the Y coordinate of the upper-left corner of the framing rectangle
w - the width of the framing rectangle
h - the height of the framing rectangle
From this program, I found that x and y appear to be at the center, and not the upper-left corner, of the framing rectangle -- or is my understanding flawed?
db