La classe: MainDrag

 1 package mousedragicon;
 2 
 3 import java.awt.Color;
 4 import java.awt.Dimension;
 5 import java.awt.EventQueue;
 6 import javax.swing.JFrame;
 7 
 8 public class MainDrag extends JFrame{
 9     private Dimension sz;
10     private int xce,yce;
11     public MainDrag(){   
12         setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
13         getContentPane().setBackground(Color.yellow); 
14         setLayout(null);
15         setSize(500,500);
16         setLocationRelativeTo(null);
17         MouseDragIcon mdi=new MouseDragIcon();        
18         add(mdi);
19         
20         setVisible(true);
21         sz=getContentPane().getSize();
22         mdi.setSize(sz);
23         
24         //Centra il pomello       
25         xce=sz.width/2-mdi.getSz().x/2;
26         yce=sz.height/2-mdi.getSz().y/2; 
27     
28         mdi.centra(xce, yce);
29         
30     }        
31     public static void main(String[] args) {
32         EventQueue.invokeLater(new Runnable() {
33 
34             @Override
35             public void run() {                
36                 new MainDrag();
37             }
38         });
39     }   
40 }

La classe: MouseDragIcon

 1 package mousedragicon;
 2 
 3 import java.awt.Dimension;
 4 import java.awt.Graphics;
 5 import java.awt.Graphics2D;
 6 import java.awt.Point;
 7 import java.awt.Shape;
 8 import java.awt.event.MouseAdapter;
 9 import java.awt.event.MouseEvent;
10 import java.awt.event.MouseMotionAdapter;
11 import java.awt.geom.Ellipse2D;
12 import java.net.URL;
13 import javax.swing.*;
14 
15 
16 public class MouseDragIcon extends JComponent { 
17     private Point mousePt;
18     private ImageIcon pon;
19     private int wp,hp,xce,yce,W,H,dx,dy;
20     private Shape shape = null;
21     private Dimension sz;
22     private Point icoPt;
23     
24     public MouseDragIcon() {        
25         pon = createImageIcon("/image/drag03.png");
26         wp=pon.getIconWidth();
27         hp=pon.getIconHeight();
28        
29         icoPt=new Point(0, 0);
30 
31         addMouseListener(new MouseAdapter() {
32             @Override
33             public void mousePressed(MouseEvent e) {
34                 mousePt = e.getPoint();
35                 repaint();
36             }
37         });
38         addMouseMotionListener(new MouseMotionAdapter() {
39             @Override
40             public void mouseDragged(MouseEvent e) {
41                 dx = e.getX() - mousePt.x;
42                 dy = e.getY() - mousePt.y;
43                 icoPt.setLocation(icoPt.x+dx,icoPt.y+dy);
44                 mousePt = e.getPoint();
45                 repaint();
46             }
47         }); 
48     }
49 
50     @Override
51     public void paintComponent(Graphics g) {
52         super.paintComponent(g);
53         Graphics2D g2d =(Graphics2D)g;  
54              
55         shape=new Ellipse2D.Float(icoPt.x ,icoPt.y ,wp,hp);         
56         pon.paintIcon(this, g2d,icoPt.x ,icoPt.y);
57     }
58     
59     @Override
60     public boolean contains(int x, int y) {
61         return shape.contains(x,y);
62     }
63     
64     public Point getSz(){
65         Point pnt =new Point(wp,hp);
66         return(pnt);
67     }
68     public void centra(int x,int y){
69         icoPt.x=x;
70         icoPt.y=y;
71         repaint();
72     }
73     
74     private ImageIcon createImageIcon(String path) {
75          URL imgURL = getClass().getResource(path);
76          if (imgURL != null) {
77              return new ImageIcon(imgURL);
78          } else {
79              System.err.println("Non è possibile trovare il file: " + path);
80            return null;
81         }
82      }
83 }