Re: Drag two images with a mouse anywhere in the frame

Daniele Futtorovic <>
Tue, 22 Mar 2011 19:13:09 +0100
On 22/03/2011 15:38, bH allegedly wrote:

Hi Daniele and John,
A big "THANKS" for your replies.
The program below takes 3 images
allows for showing them in random order
at random locations. The user then uses the mouse to
move the images to reorder. It is a work in progress.
I have not studied the entire list of your
recommendations but eventually hope to do so.

I appreciate your responses very much.

/* original:
  * Version2: 22 March 2011:
  * Three XX.png images stored in folder named "images"
  * The program takes the images puts them in random order
  * at random locations. The user then uses the mouse to
  * move the images to reorder. bH
import java.awt.EventQueue;
import java.awt.Container;
import java.awt.Component;
import java.awt.GridLayout;

import java.awt.event. MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.event.MouseEvent;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Random;

import javax.swing.JFrame;
import javax.swing. JLayeredPane;
import javax.swing.ImageIcon;
import javax.swing.JLabel;

public class LabelDragAndDropVer2 extends JFrame implements
     MouseListener, MouseMotionListener
     JLayeredPane layeredPane;
     Component dragComponent;
     int xAdjustment;
     int yAdjustment;
     private String strNumber[] = new String [3];
     private int number = 0 ;

     private Random wheel = new Random();
     int high= 60;
     int low = 20;
     int numPictures = 3;

     // two arrays stores x,y values
     int[] xPoints = new int[numPictures];
     int[] yPoints = new int[numPictures];

     public LabelDragAndDropVer2() {

     public void init() {
     // Use a Layered Pane for this this application
         layeredPane = new JLayeredPane();
         layeredPane.setLayout( null );
         layeredPane.addMouseListener( this );
         layeredPane.addMouseMotionListener( this );

         // ordering the location of picture random
         for (int i= 0;i<numPictures; i++){
             int m = wheel.nextInt(high - low + 1 ) + low;
             xPoints[i]= m;
             int n = wheel.nextInt(high - low + 1 ) + low;
             yPoints[i]= n;
             System.out.println(i+ " "+ m + " ," + n);

         for(int i = 0; i<3; i++){
             strNumber[i] = Integer.toString(i);
             number = Integer.parseInt(strNumber[i]);
         // ordering the images randomly
         List<String> inputList = Arrays.asList(strNumber);

         for (int i= 0;i<3; i++){
             number = Integer.parseInt(strNumber[i]);
             ImageIcon julia = new ImageIcon("images/MH"+
                                             number + ".png");
             JLabel label = new JLabel(julia);
             label.setLocation(xPoints[i], yPoints[i]);
             label.setSize( label.getPreferredSize() );

         Container contentPane= getContentPane();
         contentPane.setLayout(new GridLayout(1,2) );
         setSize(600,600);// frame size
      ** Determine if we clicked on a moveable component
     public void mousePressed(MouseEvent e)
         dragComponent = null;
         Component c = layeredPane.findComponentAt(e.getX(),
         if (c instanceof JLayeredPane) return;
         dragComponent = c;
         xAdjustment = dragComponent.getLocation().x - e.getX();
         yAdjustment = dragComponent.getLocation().y - e.getY();
         dragComponent.setLocation(e.getX() + xAdjustment,
                                   e.getY() + yAdjustment);
      ** Move the component around the panel
     public void mouseDragged(MouseEvent me)
         if (dragComponent == null) return;
         dragComponent.setLocation(me.getX() + xAdjustment,
                                   me.getY() + yAdjustment);
      ** Deselect the component
     public void mouseReleased(MouseEvent e)
         dragComponent = null;
     public void mouseClicked(MouseEvent e) {}
     public void mouseMoved(MouseEvent e) {}
     public void mouseEntered(MouseEvent e) {}
     public void mouseExited(MouseEvent e) {}

     public static void main(String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 new LabelDragAndDropVer2();

Looking quite good! I would however advise that you used local variables
wherever possible (case in point: wheel, number and strNumber). If you
come from a different language culture, let me note that it is neither
canonical nor even common in Java to find code with all the variable
declarations at the start of the block. Personally, I generally define
variables the closest to the point I need them.

In the same sense, I would strongly advise you made the MouseListeners
instances of an inner, possibly anonymous, class. It will make your code
a lot more readable and, again if you come from a different language,
will give you some practice with inner classes, which are invaluable
tools in Java programming.


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