Another user with applet problems

Question

I have a (should be simple) learning application that makes a window 400x400 pixels in size and fills it with random noise continuously. This works fine when run with the java command line, but when included in a html page I get these errors;
bq.      load: Engine.class can't be instantiated. \\     java.lang.InstantiationException: Engine \\     at java.lang.Class.newInstance0(Class.java:340) \\     at java.lang.Class.newInstance(Class.java:308) \\     at sun.applet.AppletPanel.createApplet(AppletPanel.java:779) \\     at sun.applet.AppletPanel.runLoader(AppletPanel.java:708) \\     at sun.applet.AppletPanel.run(AppletPanel.java:362) \\     at java.lang.Thread.run(Thread.java:619)
(in browsers this causes a lock-up, with the appletviewer it simply shows the errors)
My code is based heavily on this example file;
http://java.sun.com/docs/books/tutorial/2d/images/examples/JumbledImageApplet.java
which as I understand it allows it to run as both an application and an applet without changes
My code is...
bq.      import java.io.; // Edit: These first few lines all end in a star, but the forum's treating that as bold syntax so I've removed it\\     import java.net.; \\     import java.awt.; \\     import java.awt.event.; \\     import java.awt.image.; \\     import javax.imageio.; \\     import javax.swing.; \\     import java.util.Random; \\     public class Engine extends JApplet { \\      private static int w = 400; \\      private static int h = 400; \\      private Canvas canvas; \\      private static Engine holder; \\      private static BufferedImage bi; \\      public static void doProcess( BufferedImage bi ) { \\      Random rand = new Random(); \\      while( true ) { \\      for( int i = 0; i < 1000; i ++ ) \\      bi.setRGB( rand.nextInt( w ), rand.nextInt( h ), rand.nextInt( 0xFFFFFF ) ); \\      render( ); \\      } \\     } \\     public Engine( int ww, int hh ) { \\      w = ww; \\      h = hh; \\      } \\     public void init( ) { \\      buildUI( ); \\      bi = getBI( ); \\      doProcess( bi ); \\      } \\     public void buildUI( ) { \\      canvas = new Canvas( w, h ); \\      add( canvas ); \\      } \\     public BufferedImage getBI( ) { \\      return canvas.getBI( ); \\      } \\     public static void main( String s[] ) { \\      JFrame f = new JFrame( "Processing..." ); \\      f.addWindowListener( new WindowAdapter( ) { \\      public void windowClosing( WindowEvent e ) { \\      System.exit( 0 ); \\      } \\     } ); \\     holder = new Engine( w, h ); \\     holder.buildUI( ); \\     holder.resize( w, h ); \\     f.add( holder ); \\     f.pack( ); \\     f.setResizable( false ); \\     f.setVisible( true ); \\     bi = holder.getBI( ); \\     doProcess( bi ); \\     } \\     public static void render( ) { \\      holder.repaint( ); \\      } \\     } \\     class Canvas extends Component { \\      private BufferedImage bi; \\      int w, h; \\      public Canvas( int ww, int hh ) { \\      w = ww; \\      h = hh; \\      bi = new BufferedImage( w, h, BufferedImage.TYPE_INT_RGB ); \\      } \\     public BufferedImage getBI( ) { \\      return bi; \\      } \\     public Dimension getPreferredSize( ) { \\      return new Dimension( w, h ); \\      } \\     public void paint( Graphics gwin ) { \\      gwin.drawImage( bi, 0, 0, null ); \\      } \\     }
I'm new to the Java language and as I say this is based on an example file, so any cleanup recomendations are welcome (I think this is the most complicated way of setting pixels on a window I've ever seen!)
Edited by: DavidJE on Sep 19, 2007 9:58 AM

Answer 1

ok, I found the problem;
my Engine class only had an (int,int) constructor, and it seems the applet viewer doesn't like that. Adding an empty () constructor fixes it.
There are some new problems now, but I think I'll be able to solve them.