Something really crazy

Question

here are two codes. They're basically the same except for one line,
System.out.printf("(%d,%d)\n",c,d);which has little to do with what the whole code is supposed to do, which is to randomly erase pixels of an image.
The problem is that when you execute them, they don't run in the same way. Of course, they're different in that one of them does not print, but at least in theory, they should be able to do what they are programmed to do since they're the same code and the minor difference(the print line) does not affect the paint function anyway.
But if you try running them they don't run in the same way. Code 1, randomly erases the image once you press the button. Code 2, however does not, and immediately erases the whole thing.
A friend of mine says it has something to do with memory leak. I don't believe him unless I can get a second opinion. Watcha guys think?
You can use any picture for the ImageIcon if you're curious to see what I mean. Thanks.
CODE 1:
import javax.swing.JPanel;
import javax.swing.JFrame;
import java.awt.BorderLayout;
import javax.swing.JButton;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ImageIcon;
import java.util.Date;
import java.util.Random;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.awt.Graphics;
import java.awt.Color;
public class eraseImage2 extends JPanel implements Runnable
     private static boolean goErase;
     private boolean eraseAll;
     private ImageIcon pic;
     private Date time;
     private Random rand;
     int[] x;
     int[] y;
     int pixelCount;
     int picX;
     int picY;
     public eraseImage2()
               eraseAll = false;
               pic=new ImageIcon("ballack.jpg");
               setSize(500,500);
               picX = (getWidth()-pic.getIconWidth())/2;
               picY = (getHeight()-100-pic.getIconHeight())/2;
               x = new int[pic.getIconWidth()];
               y = new int[pic.getIconHeight()];
               for (int c=0;c<x.length;c++)
                    x[c]=0;
               for (int c=0;c<y.length;c++)
                    y[c]=0;
               goErase=false;
               time = new Date();
               rand = new Random(time.getTime());
     public void paintComponent(Graphics g)
          super.paintComponent(g);
          if (!eraseAll)
                    pic.paintIcon(this,g,picX,picY);
                    g.setColor(getBackground());
               for (int c=0;c<x.length;c++)
               if (x[c]==1)
                    for (int d=0;d<y.length;d++)
                         if (y[d]==1)     
                              g.drawLine(picX+c,picY+d,picX+c,picY+d);
                         //System.out.printf("(%d,%d)\n",c,d);
     public static void setGoErase(boolean status)
          goErase=status;
     public void run()
          int a,b;
          while (true)
               if (goErase)
                    a=rand.nextInt(x.length);
                    b=rand.nextInt(y.length);
                    x[a]=1;
                    y=1;
     //LOOK HERE: LOOK HERE! LOOK HERE:
//CODE ONE RUNS NORMALLY
                    System.out.printf("(%d,%d)\n",picX+a,picY+b);
                    // SCROLL TO SEE CODE 2 DIFFERENCE
                    repaint();
     public static void main(String args[])
          JFrame cage = new JFrame();
          eraseImage2 app = new eraseImage2();
          cage.setLayout(new BorderLayout());
          JPanel buttonPanel = new JPanel();
          JButton start = new JButton("Start");
          buttonPanel.add(start);
          start.addActionListener(
               new ActionListener()
                    public void actionPerformed(ActionEvent e)
                         if (eraseImage2.goErase==false)
                              eraseImage2.setGoErase(true);
                         else
                              eraseImage2.setGoErase(false);
          ExecutorService threadExecutor = Executors.newFixedThreadPool( 1 );
          threadExecutor.execute( app );
          cage.add(buttonPanel,BorderLayout.SOUTH);
          cage.add(app,BorderLayout.CENTER);
          cage.setSize(app.getSize());
          cage.setVisible(true);
[b]CODE 2:import javax.swing.JPanel;
import javax.swing.JFrame;
import java.awt.BorderLayout;
import javax.swing.JButton;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ImageIcon;
import java.util.Date;
import java.util.Random;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.awt.Graphics;
import java.awt.Color;
public class eraseImage2 extends JPanel implements Runnable
     private static boolean goErase;
     private boolean eraseAll;
     private ImageIcon pic;
     private Date time;
     private Random rand;
     int[] x;
     int[] y;
     int pixelCount;
     int picX;
     int picY;
     public eraseImage2()
               eraseAll = false;
               pic=new ImageIcon("ballack.jpg");
               setSize(500,500);
               picX = (getWidth()-pic.getIconWidth())/2;
               picY = (getHeight()-100-pic.getIconHeight())/2;
               x = new int[pic.getIconWidth()];
               y = new int[pic.getIconHeight()];
               for (int c=0;c<x.length;c++)
                    x[c]=0;
               for (int c=0;c<y.length;c++)
                    y[c]=0;
               goErase=false;
               time = new Date();
               rand = new Random(time.getTime());
     public void paintComponent(Graphics g)
          super.paintComponent(g);
          if (!eraseAll)
                    pic.paintIcon(this,g,picX,picY);
                    g.setColor(getBackground());
               for (int c=0;c<x.length;c++)
               if (x[c]==1)
                    for (int d=0;d<y.length;d++)
                         if (y[d]==1)     
                              g.drawLine(picX+c,picY+d,picX+c,picY+d);
                         //System.out.printf("(%d,%d)\n",c,d);
     public static void setGoErase(boolean status)
          goErase=status;
     public void run()
          int a,b;
          while (true)
               if (goErase)
                    a=rand.nextInt(x.length);
                    b=rand.nextInt(y.length);
                    x[a]=1;
                    y=1;
                    [b]
     //LOOK HERE, PRINT LINE CODE IS PRELUDED BY //COMMENTS
                    //System.out.printf("(%d,%d)\n",picX+a,picY+b);
                    repaint();
     public static void main(String args[])
          JFrame cage = new JFrame();
          eraseImage2 app = new eraseImage2();
          cage.setLayout(new BorderLayout());
          JPanel buttonPanel = new JPanel();
          JButton start = new JButton("Start");
          buttonPanel.add(start);
          start.addActionListener(
               new ActionListener()
                    public void actionPerformed(ActionEvent e)
                         if (eraseImage2.goErase==false)
                              eraseImage2.setGoErase(true);
                         else
                              eraseImage2.setGoErase(false);
          ExecutorService threadExecutor = Executors.newFixedThreadPool( 1 );
          threadExecutor.execute( app );
          cage.add(buttonPanel,BorderLayout.SOUTH);
          cage.add(app,BorderLayout.CENTER);
          cage.setSize(app.getSize());
          cage.setVisible(true);
They're the same code, but they won't run in the same way. At least on my pc.

Answer 1

Calling repaint() doesn't immediately repaint the screen, and multiple calls to repaint can well be combined to one. This happens especially in a tight loop like yours. This improves efficiency because painting is fairly slow; it lets the program do more calculations. To get the effect you want you can try using the paintImmediately method or adding a small delay to the inner loop.
See also the section on repaint managers in this article:
http://java.sun.com/products/jfc/tsc/articles/painting/index.html