Using MouseMotionListener in order to have a drag and drop effect

Question

Hello,
How is the exact syntax in order for the following code to work even for Drag and Drop effects of the drawn figures.
package tpi;
import java.awt.*;
import java.awt.event.*;
public class Desenare extends Frame{
     private Panel selPanel;
     private Choice sel;
     private Choice fond;
     private Choice lista;
     private MyCanvas canvas;
     public Desenare(String titlu){
          super(titlu);
          selPanel = new Panel(new GridLayout(6,1));
          Label label1 = new Label("Culoare");
          sel = new Choice();
          sel.addItem("Alb");
          sel.addItem("Albastru");
          sel.addItem("Verde");
          sel.addItem("Negru");
          sel.select(0);
          Label label2 = new Label("Figura");
          lista = new Choice();
          lista.addItem("Dreptunghi");
          lista.addItem("Linie");
          lista.addItem("Cerc");
          lista.select(0);
          Label label3 = new Label("Culoare Fond");
          fond = new Choice();
          fond.addItem("Negru");
          fond.addItem("Verde");
          fond.addItem("Albastru");
          fond.addItem("Alb");
          fond.select(0);
          IL itemListener = new IL();
          sel.addItemListener(itemListener);
          fond.addItemListener(itemListener);
          lista.addItemListener(itemListener);
          selPanel.add(label1);
          selPanel.add(sel);
          selPanel.add(label2);
          selPanel.add(lista);
          selPanel.add(label3);
          selPanel.add(fond);
          selPanel.setBackground(Color.LIGHT_GRAY);
          canvas = new MyCanvas();
          add("West",selPanel);
          add("Center",canvas);
          addWindowListener(new WA());
          setSize(400,300);
          setVisible(true);
     class WA extends WindowAdapter{
          public void windowClosing(WindowEvent e){
               System.exit(0);
     class IL implements ItemListener{
          public void itemStateChanged(ItemEvent event){
          canvas.repaint();
     Color genCuloare(String culoare){
          Color color;
          if (culoare.equals("Negru")) color = Color.black;
          else if (culoare.equals("Verde")) color = Color.green;
          else if (culoare.equals("Albastru")) color = Color.blue;
          else if (culoare.equals("Alb")) color = Color.white;
          else color = Color.black;
          return color;
     class MyCanvas extends Canvas{
          public void paint(Graphics g){
          String culoare = sel.getSelectedItem();
          Color color = genCuloare(culoare);
          g.setColor(color);
          color = genCuloare(fond.getSelectedItem());
          setBackground(color);
          Dimension dim = getSize();
          int cx = dim.width/2;
          int cy = dim.height/2;
          String figura = lista.getSelectedItem();
          if (figura.equals("Linie"))
          g.drawLine(cx/2,cy/2,3*cx/2,3*cy/2);
          else if (figura.equals("Dreptunghi"))
          g.fillRect(cx/2,cy/2,cx,cy);
          else if (figura.equals("Cerc"))
          g.fillOval(cx/2,cy/2,cx,cy);
          ML listener = new ML();
          canvas.addMouseMotionListener(listener);
          public class ML implements MouseMotionListener{
               @Override
               public void mouseDragged(MouseEvent arg0) {
                    // TODO Auto-generated method stub
               @Override
               public void mouseMoved(MouseEvent arg0) {
                    // TODO Auto-generated method stub
          public static void main(String []args){
          Desenare d = new Desenare("Desenare 2D");
Where exactly do i have to add the MouseMotionListener , i guess that i should add it to the canvas , and the inherited metod shoul be modified in order to use canvas.repaint() at the location where the draggin effect has ended, or if there is some other way when i press the mouse on the figure and start moving around to getX() and getY() and use the repaint method at those coordinates , wich is a drag and drop effect , i think that it would be MouseMoved , but i`m not sure, and also not sure how to use the Event Listener , where exactly ?
Thanks,
Paul

Answer 1

When you post a code, use code tags for propere formatting. Click CODE icon on the taskbar for generating code tag pair you need.
In order to do dragging the figure on the canvas or panel, you should use advanced Java 2D APIs, including Shape and its descendants. Example shown below might help, but beware, this version does not remember previous drag result for a figure over multiple lista Choice selection. Previous drag result is reset for the next selection of the same figure.
If you want to prevent flickering on the screen while dragging, use javax.swing and its components. If you have to use AWT, draw the figure into an Image or BufferedImage of full panel size and call g2.drawImage() in the paint() method.
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.event.*;
public class Desenare extends Frame{
  private Panel selPanel;
  private Choice sel;
  private Choice fond;
  private Choice lista;
  private MyCanvas canvas;
  Color fcolor, bcolor;
  enum Fig{LINE, RECT, CIRCLE};
  Fig fig;
  int xL0, yL0, xL1, yL1;
  int xR0, yR0, xR1, yR1;
  int xC0, yC0, xC1, yC1;
  int dxL, dyL, dxR, dyR, dxC, dyC;
  Shape shape;
  public Desenare(String titlu){
    super(titlu);
    selPanel = new Panel(new GridLayout(6,1));
    fcolor = bcolor = Color.white;
    dxL = dyL = dxR = dyR = dxC = dyC = 0;
    Label label1 = new Label("Culoare");
    sel = new Choice();
    sel.addItem("Alb");
    sel.addItem("Albastru");
    sel.addItem("Verde");
    sel.addItem("Negru");
    sel.select(0);
    Label label2 = new Label("Figura");
    lista = new Choice();
    lista.addItem("Dreptunghi");
    lista.addItem("Linie");
    lista.addItem("Cerc");
    lista.select(0);
    Label label3 = new Label("Culoare Fond");
    fond = new Choice();
    fond.addItem("Alb");
    fond.addItem("Albastru");
    fond.addItem("Verde");
    fond.addItem("Negru");
    fond.select(0);
    IL itemListener = new IL();
    sel.addItemListener(itemListener);
    fond.addItemListener(itemListener);
    lista.addItemListener(itemListener);
    selPanel.add(label1);
    selPanel.add(sel);
    selPanel.add(label2);
    selPanel.add(lista);
    selPanel.add(label3);
    selPanel.add(fond);
    selPanel.setBackground(Color.LIGHT_GRAY);
    canvas = new MyCanvas();
    add(selPanel, BorderLayout.WEST);
    add(canvas, BorderLayout.CENTER);
    addWindowListener(new WA());
    setSize(400, 300);
    setVisible(true);
  class WA extends WindowAdapter{
    public void windowClosing(WindowEvent e){
      System.exit(0);
  class IL implements ItemListener{
    public void itemStateChanged(ItemEvent event){
      Object o = event.getSource();
      if (o == sel){
        String culoare = sel.getSelectedItem();
        fcolor = genCuloare(culoare);
        canvas.repaint();
      else if (o == fond){
        bcolor = genCuloare(fond.getSelectedItem());
        canvas.setBackground(bcolor);
      else if (o == lista){
        String figura = lista.getSelectedItem();
        if (figura.equals("Linie")){
          fig = Fig.LINE;
        else if (figura.equals("Dreptunghi")){
          fig = Fig.RECT;
        else if (figura.equals("Cerc")){
          fig = Fig.CIRCLE;
        shape = prepareShape(fig);
        canvas.repaint();
  Shape prepareShape(Fig fig){
    Shape shape = null;
    if (fig == Fig.LINE){
      shape = new Line2D.Float(xL0, yL0, xL1, yL1);
    else if (fig == Fig.RECT){
      shape = new Rectangle2D.Float(xR0, yR0, xR1, yR1);
    else if (fig == Fig.CIRCLE){
      shape = new Ellipse2D.Float(xC0, yC0, xC1, yC1);
    return shape;
  Shape prepareShapeDrag(Fig fig){
    Shape shape = null;
    if (fig == Fig.LINE){
      shape = new Line2D.Float(xL0 + dxL, yL0 + dyL, xL1 + dxL, yL1 + dyL);
    else if (fig == Fig.RECT){
      shape = new Rectangle2D.Float(xR0 + dxR, yR0 + dyR, xR1, yR1);
    else if (fig == Fig.CIRCLE){
      shape = new Ellipse2D.Float(xC0 + dxC, yC0 + dyC, xC1, yC1);
    return shape;
  Color genCuloare(String culoare){
    Color color;
    if (culoare.equals("Negru")){
      color = Color.black;
    else if (culoare.equals("Verde")){
      color = Color.green;
    else if (culoare.equals("Albastru")){
      color = Color.blue;
    else if (culoare.equals("Alb")){
      color = Color.white;
    else{
      color = Color.black;
    return color;
  class MyCanvas extends Canvas{
    public MyCanvas(){
      setBackground(Color.white);
      ML ml = new ML();
      addMouseListener(ml);
      addMouseMotionListener(ml);
    public void paint(Graphics g){
      Graphics2D g2 = (Graphics2D)g;
      setCoords();
      g2.setPaint(fcolor);
      if (shape != null){
        g2.draw(shape);
        g2.fill(shape);
    void setCoords(){
      int w = getWidth();
      int h = getHeight();
      xL0 = w / 4;
      yL0 = h / 4;
      xL1 = xL0 * 3;
      yL1 = yL0 * 3;
      xC0 = xR0 = xL0;
      yC0 = yR0 = yL0;
      xC1 = xR1 = w / 2;
      yC1 = yR1 = h / 2;
  public class ML extends MouseInputAdapter{
    Shape s = null;
    Point p0 = null;
    Point p1 = null;
    @Override
    public void mousePressed(MouseEvent e) {
      double dist = 0.0;
      p0 = p1 = e.getPoint();
      if (shape instanceof Line2D){
        dist = ((Line2D)shape).ptSegDist(p0);
        if (dist < 2){
          s = shape;
        else{
          s = null;
      else{
        if (shape.contains(p0)){
          s = shape;
        else{
          s = null;
    @Override
    public void mouseDragged(MouseEvent e) {
      int dx, dy;
      if (s != null){
        p0 = p1;
        p1 = e.getPoint();
        dx = p1.x - p0.x;
        dy = p1.y - p0.y;
        if (s instanceof Line2D){
          dxL += dx;
          dyL += dy;
        else if (s instanceof Rectangle2D){
          dxR += dx;
          dyR += dy;
        else if (s instanceof Ellipse2D){
          dxC += dx;
          dyC += dy;
        shape = Desenare.this.prepareShapeDrag(fig);
        canvas.repaint();
  public static void main(String []args){
    Desenare d = new Desenare("Desenare 2D with Dragging support");
}