Help with game

Question

hi, im trying to make my first complex program involving applets, which is to be some take on pong. What ive been doing so far is messing with different types of input and movement in a test program called "RectRun"
i decided that im going to use the mouse wheel as the input for the moving of the paddle up and down. what im attempting to do is have the paddle "drift" almost as if it is moving on ice, which i have accomplished, but the problem is that further input from the mouse wheel will not be executed until the loop that makes it drift has completed (i hope that makes sense). so basically what i need to do is break out of the loop when a new input is received from the mouse wheel being turned, but i dont know how to tell when a new input is recieved. here is my code for RectRun so you can run it yourselves and see how the rectangle behaves because it is hard to describe :p
import java.awt.Graphics;
import java.awt.Color;
import java.awt.Font;
import java.awt.event.MouseWheelEvent;
import java.awt.event.MouseWheelListener;
import java.applet.*;
public class RectApp extends Applet implements MouseWheelListener
     private int x, y, prevy, pause, changeFactor;
     public final int WIDTH = 10, HEIGHT = 45;
     Graphics g;
    public void init()
        x = 10;
        y = 50;
        prevy = 0;
        changeFactor = 0;
        wait = new Thread();
        wait.start();
        addMouseWheelListener(this);
        setBackground(Color.BLACK);
        g = getGraphics();
     public void mouseWheelMoved(MouseWheelEvent e)
         int notches = e.getWheelRotation();
         if(notches < 0)
              for(pause = 0; pause < 100; pause += 10)
                        try{ wait.sleep(pause);} catch( InterruptedException i ){}
                        prevy = y;
                        y -= 3;
                        paint(g);
         else
              for(pause = 0; pause < 100; pause += 10)
                        try{ wait.sleep(pause);} catch( InterruptedException i ){}
                        prevy = y;
                        y += 3;
                        paint(g);
    public void paint(Graphics g)
        g.setColor(Color.GREEN);
        g.clearRect(x,prevy,WIDTH+1,HEIGHT+1);
         g.drawRect(x,y,WIDTH, HEIGHT);
         g.drawRect(0,0,499,299);
            g.drawRect(1,1,497,297);
            g.drawLine(250,0,250,300);
       public boolean isFocusTraversable() {return true;}
}Edited by: adg12012 on May 8, 2008 1:20 PM

Answer 1

adg12012 wrote:
the reason i had to do the paint(g) as opposed to repaint is because inside the loop, repaint() wouldn't execute.[http://java.sun.com/j2se/1.5.0/docs/api/java/awt/Component.html#repaint()]
As this documentation states, repaint() simply tries to call paint() at the next possible opportunity. I believe this comes in adding an event to AWT's event queue to trigger the repaint.
The trouble is, you are looping on the same thread as the event queue processing thread. Which means, the thread will only get back to processing events after your time-intensive loop has finished. In other words, the repaint event can't be processed until you give control back to the event queue processor, i.e. finish your actionListener code.
If you ever want to do time-intensive operations in a GUI application, you pretty much always want to do them on a separate thread, or your GUI will not respond until the operation is complete. Take, for example, Windows' File Explorer window. You know how frustrating it is when you click on a Network share, or a Floppy drive, when the destination doesn't exist? How the window freezes for like 2 minutes trying to establish the connection? That's because that particular application tries to find the target (a time-intensive operation) on the same thread that is driving the GUI.