Drag and dynamically add line segments?

Question

Dear all:
I draw a continuous line segments by mouse, which starts by a left
mouse click. Then if user click on another location on the screen, it
will continuously add a line segment to the screen. This process ends
with a right mouse click. In this case, all the points are shown
in a JPanel and stored in a Vector.
My question is:
after the line is shown on the screen, how can I use mouse to drag
any points on these line segments (it does not necessary need to be
the line-segment connecting points), such that the new points will be
added to the line, and original line segments' shape changed
accordingly during the mouse drag.
Example:
Step 1: A line (containing line segments], which is drawn by mouse on the Panel:
    * [left click]
      *  [left click]
      |
      |
      *  [left click]
       * [right click]
Step 2: Drag any points in the line, this does not necessary to be
original points that define the line-segments, such as the + in the
following.
      |
      + [here left click a point on the line]
      |
Step 3: If I drag the + in above figure to left, it will become:
    +  [right click, the new point and new line segment is added]
When the mouse released, the new shape is shown on the panel.How to do the dynamically drag?
Thanks in advance!

Answer 1

Try this
regards
Stas
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.ArrayList;
public class Test {
    JScrollPane scroll;
    JPanel p=new JPanel(new BorderLayout());
    Robot robot=new Robot();
    public Test()  throws Exception {
        final JFrame frame=new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(p);
        frame.getContentPane().add(new Desktop());
        frame.setBounds(0,0,350,350);
        frame.show();
    public static void main(String[] args) throws Exception {
        new Test();
class Desktop extends JPanel implements MouseListener, MouseMotionListener{
    ArrayList polyline=new ArrayList();
    Point startPoint;
    boolean dragged=false;
    int lineIndex=-1;
    public Desktop() {
        super();
        addMouseListener(this);
        addMouseMotionListener(this);
        polyline.add(new Line2D.Double(10,10,150,150));
        polyline.add(new Line2D.Double(150,150,10,300));
    public void mouseDragged(MouseEvent e) {
    public void mouseMoved(MouseEvent e) {
    public void mouseClicked(MouseEvent e) {
    public void mousePressed(MouseEvent e) {
        Point point=e.getPoint();
        Rectangle2D pointRect=new Rectangle(point.x-3,point.y-3,7,7);
        for (int i=0; i<polyline.size(); i++) {
            Line2D line=(Line2D)polyline.get(i);
            if (line.intersects(pointRect)) {
                startPoint=point;
                lineIndex=i;
                return;
        lineIndex=-1;
    public void mouseReleased(MouseEvent e) {
        if (lineIndex>=0) {
            Point2D endPoint=e.getPoint();
            Line2D line=(Line2D)polyline.get(lineIndex);
            Line2D firstPart=new Line2D.Double(line.getP1(),endPoint);
            Line2D secondPart=new Line2D.Double(endPoint,line.getP2());
            polyline.remove(lineIndex);
            polyline.add(secondPart);
            polyline.add(firstPart);
            this.repaint();
    public void mouseEntered(MouseEvent e) {
    public void mouseExited(MouseEvent e) {
    public void paint(Graphics g) {
        super.paint(g);
        g.setColor(Color.red);
        for (int i=0; i<polyline.size(); i++) {
            Line2D line=(Line2D)polyline.get(i);
            ((Graphics2D)g).draw(line);