Generate Bouncing Lines Using Applet Example

1. /*
2. Generate Bouncing Lines Using Applet Example
3. This Java example shows how to create bouncing lines using java Applet
4. example.
5. */
6.  
7. import java.awt.*;
8. import java.applet.Applet;
9.  
10. public class BouncingLines extends Applet implements Runnable {
11.  
12. Thread runner = null;
13.  
14. final static int WIDTH = 200;
15. final static int HEIGHT = 100;
16.  
17. Image image;
18. Graphics graphics;
19.  
20. // bouncing lines member variables
21. int[] x1;
22. int[] y1;
23. int[] x2;
24. int[] y2;
25.  
26. int dx1 = 2 + (int)( 3 * Math.random() );
27. int dy1 = 2 + (int)( 3 * Math.random() );
28. int dx2 = 2 + (int)( 3 * Math.random() );
29. int dy2 = 2 + (int)( 3 * Math.random() );
30. static int first = 0;
31. final static int LINES = 50;
32.  
33. public void init() {
34.  
35. // create arrays to hold the line coordinates
36. x1 = new int[LINES];
37. y1 = new int[LINES];
38. x2 = new int[LINES];
39. y2 = new int[LINES];
40.  
41. // initialise the first line
42. x1[0] = (int)( WIDTH * Math.random() );
43. y1[0] = (int)( HEIGHT * Math.random() );
44. x2[0] = (int)( WIDTH * Math.random() );
45. y2[0] = (int)( HEIGHT * Math.random() );
46.  
47. // initialise all the other lines
48. for ( int i = 1; i < LINES; i++ ) {
49.  
50. x1[i] = x1[0];
51. y1[i] = y1[0];
52. x2[i] = x2[0];
53. y2[i] = y2[0];
54. }
55. image = createImage( WIDTH, HEIGHT );
56. graphics = image.getGraphics();
57. }
58.  
59.  
60. public void start() {
61.  
62. // user visits the page, create a new thread
63. if ( runner == null ) {
64.  
65. runner = new Thread( this );
66. runner.start();
67. }
68. }
69.  
70.  
71. public void stop() {
72.  
73. // user leaves the page, stop the thread
74. if ( runner != null && runner.isAlive() )
75. runner.stop();
76.  
77. runner = null;
78. }
79.  
80.  
81. public void run() {
82.  
83. while (runner != null) {
84.  
85. repaint();
86.  
87. try {
88.  
89. Thread.sleep( 20 );
90.  
91. } catch ( InterruptedException e ) {
92.  
93. // do nothing
94. }
95. }
96. }
97.  
98.  
99. public void paint( Graphics g ) {
100.  
101. update( g );
102. }
103.  
104.  
105. public void update( Graphics g ) {
106.  
107. // clear the background to white
108.  
109. graphics.setColor( Color.black );
110. graphics.fillRect( 0, 0, WIDTH, HEIGHT );
111.  
112. // draw the lines
113. for(int r=4;r<=9;r++)
114. {
115.  
116. graphics.setColor( Color.green );
117.  
118. int line = first;
119.  
120. for ( int i = 0; i < LINES; i++ ) {
121.  
122. graphics.drawLine( x1[line], y1[line],
123. x2[line], y2[line] );
124. line++;
125. if ( line == LINES ) line = 0;
126. }
127.  
128. line = first;
129.  
130. first--;
131.  
132. if ( first < 0 ) first = LINES - 1;
133.  
134. x1[first] = x1[line];
135. y1[first] = y1[line];
136. x2[first] = x2[line];
137. y2[first] = y2[line];
138.  
139. // move the "first" line
140.  
141. if (x1[first] + dx2 < WIDTH)
142. x1[first] += dx1;
143. else
144. dx1 = -(2 + (int)( 3 * Math.random() ));
145.  
146. if (x1[first] + dx1 >= 0)
147. x1[first] += dx1;
148. else
149. dx1 = 2 + (int)( 3 * Math.random() );
150.  
151. if (y1[first] + dy1 < HEIGHT)
152. y1[first] += dy1;
153. else
154. dy1 = -(2 + (int)( 3 * Math.random() ));
155.  
156. if (y1[first] + dy1 >= 0)
157. y1[first] += dy1;
158. else
159. dy1 = 2 + (int)( 3 * Math.random() );
160.  
161. if (x2[first] + dx2 < WIDTH)
162. x2[first] += dx2;
163. else
164. dx2 = -(2 + (int)( 3 * Math.random() ));
165.  
166. if (x2[first] + dx2 >= 0)
167. x2[first] += dx2;
168. else
169. dx2 = 2 + (int)( 3 * Math.random() );
170.  
171. if (y2[first] + dy2 < HEIGHT)
172. y2[first] += dy2;
173. else
174. dy2 = -(2 + (int)( 3 * Math.random() ));
175.  
176. if (y2[first] + dy2 >= 0)
177. y2[first] += dy2;
178. else
179. dy2 = 2 + (int)( 3 * Math.random() );
180.  
181. // copy buffer to screen
182. g.drawImage( image, 0, 0, this );
183. }
184. }
185. }