Problem with repaint command.

[zgmonkey]

Hello. I am new to java and using a slightly outdated book, so I'm sure I'm just missing something silly.

This program is supposed to take a block and move it up the screen, getting slightly faster as it goes. I'm pretty sure that part works, but I just keep getting a blank screen. I've tried moving around the repaint command to different parts of the program, but the best I can do is get the screen to flicker. The book says the place it inside the move thread, but it doesn't do anything when I put it there. Does anybody know what I'm doing wrong?

I am using NetBeans 7.1, but I have also tried it in Eclipse, and it does the same thing.

//import everything:
import javax.swing.*;
import java.awt.*;

//JFrame class
public class movingBlock extends JFrame
{
    //screen size
    final int WIDTH = 900, HEIGHT = 650;
    //block speed
    double blockSpeed=0.5;
    //block
    Rectangle block = new Rectangle(WIDTH/9,HEIGHT/2,WIDTH/30,WIDTH/30);
    //constructor
    public movingBlock()
    {
        //creates JFrame
        super("Moving Block");
        setSize(WIDTH,HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
        
        //inner class
        Move m = new Move();
        m.start();
    }
    
    //draws stuff
    public void paint(Graphics g)
    {
        super.paint(g);
        //background
        g.setColor(Color.DARK_GRAY);
        g.fillRect(0,0,WIDTH,HEIGHT);
        
        //drawing the block
        g.setColor(Color.BLUE);
        g.fill3DRect(block.x,block.y,block.width,block.height,true);
        repaint();
    }
    
    private class Move extends Thread
    {
        public void run()
        {
            while(true)
            {
                try
                {
                    if(blockSpeed<=5)
                        blockSpeed+=.2;
                    block.y-=blockSpeed;
                    
                    Thread.sleep(75);
                }
                catch(Exception e)
                {
                    break;
                }
            }
        }
    }
    
    //calls constructor
    public static void main (String[] args)
    {
        new movingBlock();
    }
}

[eRaaaa]

ouch! Don`t use repaint inside the paint / paintComponent !
Try a movingBlock.this.repaint(); inside the while loop (maybe before the sleep command)
And take a look at the NamingConventions
And Usually we override paintComponent instead of paint in Swing applications!

[zgmonkey]

I know it's supposed to go in the while loop, but when I put it there I get a blank screen. Where it is the screen flickers, and that's the closest I've gotten.

movingBlock.this.repaint(); also gives a me a blank screen that flickers every 5 seconds...

[Fubarable]

Have you read any of the tutorials on Java Swing graphics? If not, you will want to. If so, you'll want to read some more: Don't draw on the top level window but rather in a component that derives from JComponent such as a JPanel or a JComponent itself. Don't paint in paint but in paintComponent. Also, consider using a Swing Timer rather than a distinct background thread.

[zgmonkey]

I copied that program word for word from the book, and you're telling me to change the whole thing...

[Fubarable]

I copied that program word for word from the book, and you're telling me to change the whole thing...

Yes. What book are you using? Please post the name so I can studiously avoid it.