Moving an Ellipse2D on mouse drag

Question

So as the title states, I would want to move the ellipse on mouse drag. I have declared ellipses first and drew them through ArrayLists (since I have 8 ellipses whi

Answer 1

So having a look through the JavaDocs for Ellipse2D, it's pretty clear that Ellipse2D doesn't expose the x/y properties publicly.

Instead, you'd have to use one of the setFrame methods instead.

This example is a slight modification of your example, which decides upon which ellipse should be moved when the mousePressed event occurs, as, to my mind, it doesn't quite make sense to do within the mouseDragged event, unless you're hopping to pick up all the ellipses. It also defines a offset between the "click" point and the ellipse's location so they won't "jump" to the mouse's position.

import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Shape;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Sample extends JFrame implements MouseListener, MouseMotionListener {

    JPanel MainPane;
    Container contentPane;
    ArrayList<Ellipse2D> redEl = new ArrayList<Ellipse2D>();
    ArrayList<Ellipse2D> whiteEl = new ArrayList<Ellipse2D>();
    Ellipse2D el1 = new Ellipse2D.Double(120, 110, 50, 50);
    Ellipse2D el2 = new Ellipse2D.Double(250, 110, 50, 50);
    Ellipse2D el3 = new Ellipse2D.Double(390, 110, 50, 50);
    Ellipse2D el4 = new Ellipse2D.Double(540, 110, 50, 50);
    Ellipse2D el5 = new Ellipse2D.Double(120, 390, 50, 50);
    Ellipse2D el6 = new Ellipse2D.Double(250, 390, 50, 50);
    Ellipse2D el7 = new Ellipse2D.Double(390, 390, 50, 50);
    Ellipse2D el8 = new Ellipse2D.Double(540, 390, 50, 50);
    int x;
    int y;
    private Point2D.Double offSet;

    public Sample() {

        redEl.add(el1);
        redEl.add(el2);
        redEl.add(el3);
        redEl.add(el4);
        whiteEl.add(el5);
        whiteEl.add(el6);
        whiteEl.add(el7);
        whiteEl.add(el8);

        MainPane = new JPanel() {
            public void paintComponent(Graphics g) {
                super.paintComponent(g);

                Graphics2D g2 = (Graphics2D) g;

                for (Shape red : redEl) {
                    g2.setColor(Color.RED);
                    g2.fill(red);
                    g2.draw(red);
                }

                for (Shape white : whiteEl) {
                    g2.setColor(Color.WHITE);
                    g2.fill(white);
                    g2.draw(white);
                }
            }
        };

        MainPane.setBackground(Color.BLACK);
        contentPane = this.getContentPane();
        contentPane.add(MainPane);
        MainPane.setLayout(null);

        setVisible(true);
        setSize(701, 701);
        setResizable(false);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        MainPane.addMouseListener(this);
        MainPane.addMouseMotionListener(this);
    }

    private Ellipse2D selected = null;

    public void mousePressed(MouseEvent e) {
        x = e.getX();
        y = e.getY();
        List<Ellipse2D> all = new ArrayList<>(redEl);
        all.addAll(whiteEl);
        for (Ellipse2D el : all) {
            if (el.contains(x, y)) {
                selected = el;
                offSet = new Point2D.Double(x - el.getX(), y - el.getY());
                break;
            }
        }
    }

    public void mouseClicked(MouseEvent e) {
        selected = null;
    }

    public void mouseReleased(MouseEvent e) {
    }

    public void mouseEntered(MouseEvent e) {
    }

    public void mouseExited(MouseEvent e) {
    }

    public void mouseDragged(MouseEvent e) {

        if (selected != null) {

            double x = e.getX() - offSet.x;
            double y = e.getY() - offSet.y;

            Rectangle2D bounds = selected.getBounds2D();
            bounds.setFrame(new Rectangle2D.Double(x, y, bounds.getWidth(), bounds.getHeight()));

            selected.setFrame(bounds);
            repaint();

        }
    }

    public void mouseMoved(MouseEvent e) {
    }

    public static void main(String args[]) {
        new Sample();
    }

}