1 /*
2 * File: mInnerApplet.java
3 *
4 * MouseEvents, movable objects, and inner classes
5 *
6 * Note: The private modifier was removed from some of the
7 * variables so that the inner classes have access.
8 * Evidently this is a longstanding bug in JDK 1.1
9 * (see page 103 of the tiger book).
10 */
11
12 import java.applet.*;
13 import java.awt.*;
14 import java.awt.event.*;
15
16 public class mInnerApplet extends Applet {
17
18 // Instance variables:
19 /* private */ int numObj = 3; // number of movable objects
20 /* private */ mPoint object[]; // array of movable objects
21 private Image buffer; // image object for double buffering
22 private Graphics gOffScreen; // graphics object for double buffering
23
24 // Mouse handling variables:
25 /* private */ int current = -1;
26 /* private */ int hit = -1;
27 /* private */ int xoffset = 0;
28 /* private */ int yoffset = 0;
29
30 // Colors:
31 /* private */ Color objColor = Color.cyan;
32 /* private */ Color objColorSelect = Color.red;
33 private Color bgColor = Color.black;
34 private Color fgColor = Color.white;
35
36 public void init() {
37 setBackground( bgColor );
38 setForeground( fgColor );
39
40 // Instantiate object array:
41 object = new mPoint[ numObj ];
42
43 // Instantiate a rectangle:
44 object[0] = new mRectangle( 10, 10, 100, 100 );
45 object[0].setColor( objColor );
46
47 // Instantiate a circle:
48 object[1] = new mOval( 200, 10, 100, 100 );
49 object[1].setColor( objColor );
50
51 // Instantiate a triangle:
52 object[2] = new mTriangle( 10, 200, 100, 100 );
53 object[2].setColor( objColor );
54
55 // Create an off-screen image for double buffering:
56 buffer = createImage( getSize().width, getSize().height );
57 // Get off-screen graphics context:
58 gOffScreen = buffer.getGraphics();
59
60 // Register the applet to listen for MouseEvents via
61 // an inner class (defined below):
62 this.addMouseMotionListener( new MouseMotionHandler() );
63
64 // Register the applet to listen for MouseEvents via
65 // an *anonymous* inner class:
66 this.addMouseListener(
67 new MouseAdapter() {
68
69 public void mousePressed( MouseEvent e ) {
70 current = hit;
71 if ( current != -1 ) {
72 xoffset = object[ current ].getX() - e.getX();
73 yoffset = object[ current ].getY() - e.getY();
74 }
75 }
76
77 public void mouseReleased( MouseEvent e ) {
78 current = -1;
79 }
80
81 }
82 );
83
84 } // end method init()
85
86 // A type of inner class called a "member class":
87 class MouseMotionHandler extends MouseMotionAdapter {
88
89 public void mouseMoved( MouseEvent e ) {
90 // Determine which object contains the cursor (if any):
91 hit = -1;
92 for ( int i = 0; i < numObj; i++ ) {
93 if ( object[i].isInside( e.getX(), e.getY() ) ) {
94 hit = i;
95 break;
96 }
97 }
98 // Color all objects:
99 Color color;
100 for ( int i = 0; i < numObj; i++ ) {
101 color = ( i == hit ) ? objColorSelect : objColor;
102 object[i].setColor( color );
103 }
104 repaint();
105 }
106
107 public void mouseDragged( MouseEvent e ) {
108 if ( current != -1 ) {
109 int x = e.getX() + xoffset;
110 int y = e.getY() + yoffset;
111 object[ current ].setPoint( x, y );
112 repaint();
113 }
114 }
115
116 }
117
118 // Override java.awt.Component.update:
119 public void update( Graphics g ) {
120 // Fill background:
121 gOffScreen.setColor( getBackground() );
122 gOffScreen.fillRect( 1, 1, getSize().width - 2, getSize().height - 2 );
123 // Draw boundary:
124 gOffScreen.setColor( getForeground() );
125 gOffScreen.drawRect( 0, 0, getSize().width - 1, getSize().height - 1 );
126 paint( gOffScreen );
127
128 // Draw the buffer in the applet window:
129 g.drawImage( buffer, 0, 0, this );
130 }
131
132 // Override java.awt.Component.paint:
133 public void paint( Graphics g ) {
134 // Paint each object:
135 for ( int i = 0; i < numObj; i++ )
136 object[i].paint(g);
137 }
138
139 }
140