带有MediaTracker，线程和计时器的Java动画小程序

Question

I have 3 questions about my animation project.

1. Is the structure of the program correct (see below)
2. My first image (from an array) isn't behaving properly. Sometimes it pops up and then disappears, and then the rest of the images display correctly.
3. How do I control when the audio clip starts to play. It also sometimes sounds like a needle is ripping across a record...?

REGARDING THE PROGRAM's STRUCTURE: Are the following in the right order:

IN INIT:

1. Set applet size.
2. Run a timer task with a sleep time
3. Get the sound file.
4. Get the images from the array.
5. Initialize the MediaTracker object and tell it to "wait for all" images.
6. Play the sound file.

IN START(Graphics g) 1. Draw the applet and load the first image of the array

IN START: 1. Check the threads for null values, if not null, start them

IN RUN: 1. Use a variable "iPictureNumber" to iterate through the images in sequential order also using repaint and Thread.sleep methods

IN UPDATE: 1. Draw the applet again.

---

This code is an updated version of another program I have that didn't use threads, so I'm not sure if this is the correct structure. My goal is to use best practices with this type of simple program. I can provide the images and sound in a zip file if needed. Please advise, thanks in advance. HERE IS THE CODE:

// Java animation project with array of images and 1 sound file using threads

 import java.net.*;
 import java.io.*;
 import java.lang.*;
 import java.awt.*;
 import java.awt.event.*;
 import java.awt.Frame;
 import java.awt.Graphics;
 import java.awt.Image;
 import java.awt.MediaTracker;
 import java.applet.Applet;
 import java.applet.AudioClip;
 import java.util.*;

 public class c_TrainAnimation extends Applet implements Runnable 
  {
     Image trainAndBush[];
     int totalImages = 17, 
     currentImage = 0,             // Set current image array subscript to 0
     sleepTime = 900;
     Image imageCurrent;  // Set to the matching image in "trainAndBush" Array
     MediaTracker myImageTracker;
     Timer myTimer; 
     Thread threadTrainAnimation = new Thread(this);
     Thread threadSoundFile = new Thread(this); 
     AudioClip mySound; 

     public void init()
     {
    setSize(400,400);   

        myTimer = new Timer(true);
    myTimer.schedule( new TimerTask() 
          { 

              public void run() 
               { repaint();}

            } // end TimerTask

               ,0,sleepTime);

       mySound = getAudioClip(getDocumentBase(), "onpoint.au");
       trainAndBush = new Image[ totalImages ];

       // Load the array of images into the Applet when it begins executing
        for( int i = 0; i  < trainAndBush.length; i++ )
       {    
             trainAndBush[i] = getImage(getDocumentBase(),
              "Hill" + (i + 1) + ".jpg" );      

        myImageTracker = new MediaTracker( this ); 

        // Give the images an ID number to pass to MediaTracker
        myImageTracker.addImage(trainAndBush[i], i);

        // Tell MediaTracker to wait until all images are loaded
          try
    {
        myImageTracker.waitForAll();
    }
    catch(Exception e) {}

         mySound.play();

         }   // end for loop
     }       // end init

     // check threads for null values and then start threads
     public void start()
      {
     if (threadTrainAnimation != null )
        threadTrainAnimation.start();
     if (threadSoundFile != null )
    threadSoundFile.start();
      }

     // Draw the applet with the first image of the array
     public void start(Graphics g)
      {
     g.drawImage(trainAndBush[0],50,50,300,300, this );
     currentImage = 0;                       
      }

      // Set "imageCurrent"to appropriate "trainAndBush image" in the array and_
         loop through  
     public void run()
       {
     int iPictureNumber[] = {0, 1, 2, 3,4,5,6,7,8,9,10,11,12,13,14,15,16};
       while( true )
    {   
          for( int i = 0; i < iPictureNumber.length; i++ )
           {
         imageCurrent = trainAndBush[iPictureNumber[i]];
         repaint();
       try
        {
         Thread.sleep( sleepTime ); 
        }
        catch( InterruptedException e) {}

         }  // end for loop
       }   // end while statement
     }  // end run 

     public void update(Graphics g)
      {
    g.drawImage( imageCurrent, 50, 50, 300, 300, this );
      }

    } // end of Applet

Answer 1

I wouldn't use Applet , use JApplet , it will solve dozens of problems off the bat ;)

I probably would probably use separate Runnables for the threadTrainAnimation and threadSoundFile , but I've not had much experience with sound in the past. The problem I see though is you have two threads accessing the portion of code simultaneously doing the same thing. This is just making a mess of things.

You need to figure out how to sync the sound and the animation.

The use of the java.util.Timer is incorrect for what you are trying to achieve, it's also overkill given the fact that you have threadTrainAnimation running, as they are generally doing the same thing. In this case I'd probably just get rid of it. In the future, you're better of using javax.swing.Timer as it provides better support for the Event Dispatching Thread

I, personally, wouldn't load my resources in the init method the way you are. This is going to slow down the loading of the applet and make users upset. You'd be better putting up a nice "loading" image and use a Thread to perform the loading. Once done, using something like SwingUtilities.invokeLater to start the animation.

Don't override the update method, you should override the paint method instead.

It's also possible that images are been changed faster then they can be painted, you may want to give some thought to this as well - that is the run method may execute a number of times before paint is called

As a suggestion, I'd read through

• Concurrency in Swing
• Performing Custom Painting
• Painting in AWT and Swing
• How to make Applets (as they discuss animation here)

If you're serious about animation, I'd also check out

• TimingFramework and/or
• Trident

Which are animation frameworks for Java