Drag Demo

01: /** DragDemo.java - Mouse drag example dual application/applet
02:     @author Fred Swartz
03:     @version 2004-04-15
04: */
05: // "appletviewer DragDemo.java" works because of the following line.
06: // <applet code="DragDemo.class" height="200" width="200"></applet>
07: import java.awt.*;
08: import java.awt.event.*;
09: import javax.swing.*;
10: import javax.swing.event.*;
11: 
12: /** This is an application because it has a main method.
13:     It's also an applet because it extends JApplet.
14: */
15: 
16: public class DragDemo extends JApplet {
17:     public static void main(String[] args) {
18:         JFrame window = new JFrame();
19:         window.setTitle("Drag Demo");
20:         window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
21:         window.setContentPane(new DragBallPanel());
22:         window.pack();
23:         window.setVisible(true);
24:     }
25:     
26:     public DragDemo() {
27:         this.setContentPane(new DragBallPanel());
28:     }
29: }
30: 

01: /** DragBallPanel.java - Panel that allows dragging a ball around.
02:     @author Fred Swartz
03:     @version 2004-04-15
04: */
05: 
06: import java.awt.*;
07: import java.awt.event.*;
08: import javax.swing.*;
09: 
10: /** When the mousePressed listener is called to position is tested
11:     to see if it's in the area of the ball.  If it is, 
12:     (1) _canDrag is set true meaning pay attention to the MouseDragged events.  
13:     (2) Record where in the ball (relative to the upper left coordinates) 
14:         the mouse was clicked, because it looks best if we drag from there.
15: */
16: 
17: public class DragBallPanel extends JPanel implements MouseListener, MouseMotionListener {
18: 
19:     private static final int BALL_DIAMETER = 40; // Diameter of ball
20:     //--- instance variables
21:     /** Ball coords.  Changed by mouse listeners.  Used by paintComponent. */
22:     private int _ballX     = 50;   // x coord - set from drag
23:     private int _ballY     = 50;   // y coord - set from drag
24: 
25:     /** Position in ball of mouse press to make dragging look better. */
26:     private int _dragFromX = 0;    // pressed this far inside ball's
27:     private int _dragFromY = 0;    // bounding box.
28: 
29:     /** true means mouse was pressed in ball and still in panel.*/
30:     private boolean _canDrag  = false;
31: 
32:     /** Constructor sets size, colors, and adds mouse listeners.*/
33:     public DragBallPanel() {
34:         setPreferredSize(new Dimension(200, 200));
35:         setBackground(Color.blue);
36:         setForeground(Color.yellow);
37:         //--- Add the mouse listeners.
38:         this.addMouseListener(this); 
39:         this.addMouseMotionListener(this);
40:     }
41: 
42:     /** Ball is drawn at the last recorded mouse listener coordinates. */
43:     public void paintComponent(Graphics g) {
44:         super.paintComponent(g);   // Required for background.
45:         g.fillOval(_ballX, _ballY, BALL_DIAMETER, BALL_DIAMETER);
46:     }//end paintComponent
47: 
48:     /** Set _canDrag if the click is in the ball (or in the bounding
49:         box, which is lazy, but close enuf for this program).
50:         Remember displacement (dragFromX and Y) in the ball
51:         to use as relative point to display while dragging.
52:     */
53:     public void mousePressed(MouseEvent e) {
54:         int x = e.getX();   // Save the x coord of the click
55:         int y = e.getY();   // Save the y coord of the click
56: 
57:         if (x >= _ballX && x <= (_ballX + BALL_DIAMETER)
58:               && y >= _ballY && y <= (_ballY + BALL_DIAMETER)) {
59:             _canDrag = true;
60:             _dragFromX = x - _ballX;  // how far from left
61:             _dragFromY = y - _ballY;  // how far from top
62:         } else {
63:             _canDrag = false;
64:         }
65:     }
66: 
67: 
68:     /** Set x,y  to mouse position and repaint. */
69:     public void mouseDragged(MouseEvent e) {
70:         if (_canDrag) {   // True only if button was pressed inside ball.
71:             //--- Ball pos from mouse and original click displacement
72:             _ballX = e.getX() - _dragFromX;
73:             _ballY = e.getY() - _dragFromY;
74: 
75:             //--- Don't move the ball off the screen sides
76:             _ballX = Math.max(_ballX, 0);
77:             _ballX = Math.min(_ballX, getWidth() - BALL_DIAMETER);
78: 
79:             //--- Don't move the ball off top or bottom
80:             _ballY = Math.max(_ballY, 0);
81:             _ballY = Math.min(_ballY, getHeight() - BALL_DIAMETER);
82: 
83:             this.repaint(); // Repaint because position changed.
84:         }
85:     }
86: 
87:     /** Turn off dragging if mouse exits panel. */
88:     public void mouseExited(MouseEvent e) {
89:         _canDrag = false;
90:     }
91: 
92:     public void mouseMoved   (MouseEvent e) {}  // ignore these events
93:     public void mouseEntered (MouseEvent e) {}  // ignore these events
94:     public void mouseClicked (MouseEvent e) {}  // ignore these events
95:     public void mouseReleased(MouseEvent e) {}  // ignore these events
96: }
97: