java draw line as the mouse is moved

Question

I would like to add a feature to my application which allows the user to draw a straight line by clicking the mouse at the start location and releasing it at the end locatio

Answer 1

Try this...Draw a red line on the screen as the mouse is moved (dragged).

public static void main(String args[]) throws Exception {
    JFrame f = new JFrame("Draw a Red Line");
    f.setSize(300, 300);
    f.setLocation(300, 300);
    f.setResizable(false);
    JPanel p = new JPanel() {
        Point pointStart = null;
        Point pointEnd   = null;
        {
            addMouseListener(new MouseAdapter() {
                public void mousePressed(MouseEvent e) {
                    pointStart = e.getPoint();
                }

                public void mouseReleased(MouseEvent e) {
                    pointStart = null;
                }
            });
            addMouseMotionListener(new MouseMotionAdapter() {
                public void mouseMoved(MouseEvent e) {
                    pointEnd = e.getPoint();
                }

                public void mouseDragged(MouseEvent e) {
                    pointEnd = e.getPoint();
                    repaint();
                }
            });
        }
        public void paint(Graphics g) {
            super.paint(g);
            if (pointStart != null) {
                g.setColor(Color.RED);
                g.drawLine(pointStart.x, pointStart.y, pointEnd.x, pointEnd.y);
            }
        }
    };
    f.add(p);
    f.setVisible(true); 
}

Answer 2

    JFrame frame = new JFrame("Lines");

    frame.add(new JComponent() {
        private Shape line = null;
        {
            line = new Line2D.Double(100, 100, 200, 200);
            prevPoint = new Point();
            newPoint = new Point();

            MouseAdapter mouseAdapter = new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    prevPoint = e.getPoint();
                    System.out.println("Prev Point=" + prevPoint.toString());
                    repaint();
                }

                @Override
                public void mouseDragged(MouseEvent e) {
                    int dx = 0;
                    int dy = 0;

                    dx = (int) (prevPoint.x - e.getPoint().getX());
                    dy = (int) (prevPoint.y - e.getPoint().getY());

                    Line2D shape = (Line2D) line;

                    int x1 = (int) (shape.getX1() - dx);
                    int y1 = (int) (shape.getY1() - dy);

                    int x2 = (int) (shape.getX2() - dx);
                    int y2 = (int) (shape.getY2() - dy);

                    Point startPoint = new Point(x1, y1);
                    Point endPoint = new Point(x2, y2);

                    if (shape != null) {
                        shape.setLine(startPoint, endPoint);
                        prevPoint = e.getPoint();
                        repaint();
                    }
                }

                @Override
                public void mouseReleased(MouseEvent e) {
                    repaint();
                }

            };
            addMouseListener(mouseAdapter);
            addMouseMotionListener(mouseAdapter);
        }

        @Override
        protected void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D) g;
            g2d.setPaint(Color.BLUE);
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                    RenderingHints.VALUE_ANTIALIAS_ON);
            if (line != null) {
                g2d.draw(line);
            }
        }
    });
    frame.setSize(650, 400);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

This will move the line as the mouse is moved.. Hope this helps..

Answer 3

The MouseListener interface is your friend for this. You can just implement mousePressed and mouseReleased functions. The MouseListener interface has the following methods that you can play around with:

public void mouseEntered(MouseEvent mouse){ }   
public void mouseExited(MouseEvent mouse){ }
public void mousePressed(MouseEvent mouse){ }
public void mouseReleased(MouseEvent mouse){ }