How to fix this code to move this shape?

Hi guys

Below code can draw a polygon whenever the mouse is pressed, but it is also supposed to drag the polygon to move to anywhere the mouse is released. But the polygon doesn't move at all.

Does anyone know how to fix it?

I believe it must be something wrong in OctagonPanel class, please see my OctagonPanel class below:
(public class Octagon extends Polygon {....} and public class Main {...} are omitted here.)

Code:

---

public class OctagonPanel extends JPanel
{
    private Octagon octagon;
    private Octagon selectedOctagon = null;
    private ArrayList<Octagon> lstOctagon = new ArrayList<Octagon>();
   
    static Random generator = new Random();
    int oldx, oldy, newx, newy;
    boolean dragging = false;

    public OctagonPanel()
    {
      addMouseListener (new OctagonsListener());
      addMouseMotionListener (new OctagonsListener());
    }

  public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        for(Octagon o : lstOctagon)
        {
            o.draw(g);
        }
    }

    private class OctagonsListener implements MouseListener, MouseMotionListener
    {
        public void mousePressed (MouseEvent e)
        {
            oldx = e.getX();
            oldy = e.getY();

            for(Octagon o : lstOctagon)
            {
              if(o.contains(oldx, oldy))
              {
                  selectedOctagon = o;
                  dragging = true;
              }
            }
            if(selectedOctagon == null)
            {
                int n = generator.nextInt(80);
                int[] newx = {oldx, oldx + n, oldx + n, oldx, oldx - 2*n, oldx - 3*n, oldx - 3*n, oldx - 2*n};
                int[] newy = {oldy, oldy + n, oldy + 2*n, oldy + 3*n, oldy + 3*n, oldy + 2*n, oldy + n, oldy};
                octagon = new Octagon(newx, newy, 8);

                lstOctagon.add(octagon);
                repaint();
            }
          }

        public void mouseReleased(MouseEvent e)
        {
            if(dragging = true)
            {
                repaint();
            }
            selectedOctagon = null;
        }
        public void mouseClicked(MouseEvent e)
        {
        }
        public void mouseMoved(MouseEvent e) {}
        public void mouseDragged(MouseEvent e)
        {
            newx = e.getX();
            newy = e.getY();
            int xtrans = newx - oldx;
            int ytrans = newy - oldy;
            selectedOctagon.translate(xtrans,ytrans);
            repaint();

        }
        public void mouseEntered(MouseEvent e) {}
        public void mouseExited(MouseEvent e) {}
    }

 }

---

Thanks heaps

Hi guys, no one wants to say something yet? :)

Quote:

---

if(dragging = true)

---

Do you know what that line does?

Also, you have two different OctagonListeners added as MouseListener and MouseMotionListener. The one instance doesn't automagically have the same field values as the other.

And we have no idea what the methods in your Octagon class do.

db

db, thanks for a say. I wanted to make

Quote:

---

if(dragging = true)

---

show the particular shape is selected, then it can be moved. If that is not a right way to do, what should it look like?
I tried - it doesn't make a difference if just "MouseListener" is added or both "MouseListener and MouseMotionListener" added.
I am surprised that you said it might have something to do with Octagon class, as I thought it must be wrong in the methods of mousePressed, mouseReleased, mouseDragged. Ok, here we go:

Quote:

---

import java.awt.*;
import java.util.Random;

public class Octagon extends Polygon // so polygon's methods can be used on octagon
{
private int[] x; //= {150, 175, 175, 150, 100, 75, 75, 100};
private int[] y; // = {75, 100, 150, 175, 175, 150, 100, 75};
private Color color;
static Random generator = new Random();

public Octagon(int[]x, int[]y, int n)
{
this.x = x;
this.y = y;
color = new Color(Math.abs(generator.nextInt())% 16777216);
}

void draw(Graphics g)
{
g.setColor(color);
g.fillPolygon(x, y, 8);
}

}

---

Thanks guys, please keep talking here.

Hi guys, don't keep silent, I need your say here. :)

Code:

---

if (dragging = true)

---

will set dragging to true. You were probably wanting to do this instead:

Code:

---

if (dragging == true)

---

But even better, to prevent risk of this nonsense is to just simply do this:

Code:

---

if (dragging)

---

In addition, you need to do some debugging which can sometimes be simply done by adding print statements in your code. For example check out the results from these changes:

Code:

---


  private class OctagonsListener implements MouseListener, MouseMotionListener {
      public void mousePressed(MouseEvent e) {
        oldx = e.getX();
        oldy = e.getY();

        for (Octagon o : lstOctagon) {
           
            //!! added:  Show the bounds of all Octagons in the list.
            System.out.printf("rect: %s%n", o.getBounds().toString());
           
           
            if (o.contains(oldx, oldy)) {
             
            //!! added: see if we've selected one.
              System.out.printf("YES! This rect has it: %s%n", o.getBounds().toString());
             
             
              selectedOctagon = o;
              dragging = true;
            }
        }
        System.out.println(); //!! added
        System.out.println();

---

Are you finding all your Octagons have 0 size and 0 location? Perhaps you need to call a super constructor in your Octagon constructor so that the parent class can register the points?

Thank you Fubarable for your suggestion, now I think I have found out a big error here:
selectedOctagon never got selected in the methods private Octagon hitTest(MouseEvent e) and public void mousePressed (MouseEvent e).
(Because 1., mouseClicked and mouseDragged can't act properly.)
So how to fix that part? ..Thank you so much!

Code:

---

import java.awt.event.*;
import java.awt.*;
import javax.swing.JPanel;
import java.util.ArrayList;
import java.util.Random;

public class OctagonPanel extends JPanel
{
    private Octagon octagon;
    private Octagon selectedOctagon = null;
    private ArrayList<Octagon> lstOctagon = new ArrayList<Octagon>();
    static Random generator = new Random();
    int oldx, oldy, difx, dify, newx, newy;

    public OctagonPanel()
    {
        addMouseListener(new OctagonsListener());
        addMouseMotionListener(new OctagonsListener());
    }

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g); //optional here
        for(Octagon o : lstOctagon)
        {
            o.draw(g);
        }

    }

    private class OctagonsListener implements MouseListener, MouseMotionListener
    {
        int n;

        private Octagon hitTest(MouseEvent e)
        {
            Octagon hitO = null;
            for (Octagon o : lstOctagon)
            {
                if (o.contains(e.getX(), e.getY()))
                {
                    hitO = o;
                    break;
                }
            }
            return hitO;
        }

        public void mousePressed (MouseEvent e)
        {
            selectedOctagon = hitTest(e);
        }
        public void mouseClicked(MouseEvent e)
        {
            oldx = e.getX();
            oldy = e.getY();

            if(selectedOctagon == null)
            {
                System.out.println(oldx);
                n = generator.nextInt(50);
                int[]x = {oldx, oldx + n, oldx + n, oldx, oldx - 2*n, oldx - 3*n, oldx - 3*n, oldx - 2*n};
                int[]y = {oldy, oldy + n, oldy + 2*n, oldy + 3*n, oldy + 3*n, oldy + 2*n, oldy + n, oldy};

                octagon = new Octagon(x, y, 8);
                lstOctagon.add(octagon);

                repaint();
            }

        }
        public void mouseReleased(MouseEvent e)
        {
            //selectedOctagon = null;
            repaint();
        }

        public void mouseMoved(MouseEvent e)
        {
        }
        public void mouseDragged(MouseEvent e)
        {
              newx = e.getX(); newy = e.getY();
              if(selectedOctagon != null)
              {
                  difx = newx - oldx; dify = newy - oldy;
                  selectedOctagon.translate(difx, dify);
                  repaint();
            }

        }
        public void mouseEntered(MouseEvent e) {}
        public void mouseExited(MouseEvent e) {}
    }

}

---

:) Above problem is solved.