Mouse detecting object component

Question

I'm writting an applet in which there're 3 objects(same class) on the screen, when I clicked and dragged the object, it'll move along with the mouse. I'm having trouble to let the mouse recognise which object it is clicked and dragged. Can anyone please help me? I'm new to Java and I need to slove this problem as soon as I can. Thanks!

Answer 1

You didn't say what kind of objects you are trying to move. Looking at your earlier threads it appears you were working with graphics (as opposed to components like Panels or Labels). Here's an example of detecting and moving graphic shapes in the AWT. Swing is a little easier to do this in because of the double buffering. I made it so you can run it in either j2se 1.4 or the newer 1.5 (which requires generics).
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import java.util.List;
import javax.swing.event.MouseInputAdapter;
public class Detection
    public Detection()
        DetectionPanel detectionPanel = new DetectionPanel();
        Detector detector = new Detector(detectionPanel);
        detectionPanel.addMouseListener(detector);
        detectionPanel.addMouseMotionListener(detector);
        Frame f = new Frame();
        f.addWindowListener(new WindowAdapter()
            public void windowClosing(WindowEvent e)
                System.exit(0);
        f.add(detectionPanel);
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    public static void main(String[] args)
        new Detection();
class DetectionPanel extends Panel
    List <RectangularShape> shapes;                                     // j2se 1.5
    // List shapes;                                                     // j2se 1.4
    boolean firstTime;
    public DetectionPanel()
        shapes = new ArrayList<RectangularShape>();                     // j2se 1.5
        // shapes = new ArrayList();                                    // j2se 1.4
        firstTime = true;
    public void paint(Graphics g)
        super.paint(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        if(firstTime)
            initShapes();
        for(int j = 0; j < shapes.size(); j++)
            g2.draw(shapes.get(j));                                     // j2se 1.5
            // g2.draw((RectangularShape)shapes.get(j));                // j2se 1.4
    private void initShapes()
        int w = getWidth();
        int h = getHeight();
        int dia = Math.min(w,h)/4;
        shapes.add(new Rectangle(2*w/3, 2*h/3, dia, dia));
        shapes.add(new Ellipse2D.Double(w/4 - dia/2, h/3 - dia/2, dia, dia));
        firstTime = false;
    public void moveShape(int index, int x, int y)
        RectangularShape rs = shapes.get(index);                        // j2se 1.5
        // RectangularShape rs = (RectangularShape)shapes.get(index);   // j2se 1.4
        Rectangle clip = new Rectangle();
        clip.x = (int)(x < rs.getX() ? x : rs.getX());
        clip.y = (int)(y < rs.getY() ? y : rs.getY());
        clip.width  = (int)(clip.x + rs.getWidth());
        clip.height = (int)(clip.y + rs.getHeight());
        rs.setFrame(x, y, rs.getWidth(), rs.getHeight());
        repaint(clip.x, clip.y, clip.width, clip.height);
    public List<RectangularShape> getShapes()                           // j2se 1.5
    // public List getShapes()                                          // j2se 1.4
        return shapes;
class Detector extends MouseInputAdapter
    DetectionPanel detectionPanel;
    int selectedIndex;
    Point offset;
    boolean dragging;
    public Detector(DetectionPanel dp)
        detectionPanel = dp;
        offset = new Point();
        dragging = false;
    public void mousePressed(MouseEvent e)
        Point p = e.getPoint();
        List<RectangularShape> list = detectionPanel.getShapes();       // j2se 1.5
        // List list = detectionPanel.getShapes();                      // j2se 1.4
        for(int j = 0; j < list.size(); j++)
            RectangularShape rs = list.get(j);                          // j2se 1.5
            // RectangularShape rs = (RectangularShape)list.get(j);     // j2se 1.4
            if(rs.contains(p))
                offset.x = (int)(p.x - rs.getX());
                offset.y = (int)(p.y - rs.getY());
                dragging = true;
                selectedIndex = j;
                break;
    public void mouseReleased(MouseEvent e)
        dragging = false;
    public void mouseDragged(MouseEvent e)
        if(dragging)
            int x = e.getX() - offset.x;
            int y = e.getY() - offset.y;
            detectionPanel.moveShape(selectedIndex, x, y);
}