repaint not working in JFrame

gsquare567 · **Posted:** Thu Apr 10, 2008 8:16 am

i want it to repaint after waiting 50 milliseconds, but the frame will not repaint. stars (********) are next to it.

code:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;

public class RandomWalker extends JFrame implements ActionListener
{
public static int width = 800, height = 480;
public static int startX, startY, stickX = width/2, stickY = height/2;
public static int totalSteps = 0, currentStep = 0;

public static double randomAngle = 0, distance = 0;

public JButton quitB, startB;
public JLabel enterStepsL;
public JTextField enterStepsTF, enterWidthTF;
public static RandomWalker frame;
public static Date lastTime;

public RandomWalker()
{
super("Random Walker by Garrett Gottlieb");
setSize(width, height);
setLayout(null); // using null layout, it is the most customizable

enterWidthTF = new JTextField("Enter width here (< 800)");
enterWidthTF.setBounds(0, 5, 200, 25);

enterStepsTF = new JTextField("Enter # steps here");
enterStepsTF.setBounds(200, 5, 200, 25);

startB = new JButton("Start");
startB.setBounds(400, 0, 100, 30);

quitB = new JButton("Quit");
quitB.setBounds(500, 0, 100, 30);

startB.addActionListener(this);
quitB.addActionListener(this);

add(enterWidthTF);
add(enterStepsTF);
add(startB);
add(quitB);

setVisible(true);
}

public void paint(Graphics g)
{
g.clearRect(0, 0, width + 100, height + 120); // clear screen
// draw ubercool stickman
g.drawOval(stickX, stickY, 40, 40); // head
g.drawLine(stickX + 20, stickY + 40, stickX + 20, stickY + 80); // body
g.drawLine(stickX + 20, stickY + 80, stickX, stickY + 120); // left leg
g.drawLine(stickX + 20, stickY + 80, stickX + 40, stickY + 120); // right leg
g.drawLine(stickX + 20, stickY + 65, stickX - 20, stickY + 50); // left arm
g.drawLine(stickX + 20, stickY + 65, stickX + 60, stickY + 50); // right arm
g.drawString(distance + " pixels away after " + currentStep + " steps.", stickX, stickY - 30);
}

public static void main(String[] args)
{
frame = new RandomWalker();
}

public static void doRandomWalk()
{
stickX = width/2;
stickY = height/2;

startX = stickX;
startY = stickY;

frame.repaint();

for(int i = 0; i < totalSteps; i++)
{
randomAngle = Math.random() * Math.PI * 2;

stickX += Math.sin(randomAngle) * 10;
stickY += Math.cos(randomAngle) * 10;
//System.out.println(stickX + ", " + stickY + " minus " + startX + ", " + startY);

distance = Math.round(
Math.sqrt(
Math.pow(stickX - startX, 2) + Math.pow(stickY - startY, 2)
)
);

if(stickX > width - 100)
{
stickX = 20;
}
else if(stickX < 20)
{
stickX = width - 100;
}

if(stickY > height - 120)
{
stickY = 80;
}
else if(stickY < 80)
{
stickY = height - 120;
}

currentStep = i + 1;
frame.repaint();// **************************

lastTime = new Date();
while((new Date()).getTime() - lastTime.getTime() < 50) {frame.repaint();} // **********
}
}

public void actionPerformed(ActionEvent e)
{
Object source = e.getSource();

if(source == startB)
{
totalSteps = Integer.parseInt(enterStepsTF.getText());
width = Integer.parseInt(enterWidthTF.getText());
frame.setSize(width, height);
doRandomWalk();
}
else
System.exit(0);
}
}

OneOffDriveByPoster · **Posted:** Thu Apr 10, 2008 11:42 am

The repaint() will not call paint() until after you are finished your random walking loop. IIRC the callbacks are called from the same thread so doRandomWalk() and paint() will not run at the same time (unless if one calls the other).

A bad solution (force paint)

Java:

frame.paint(frame.getGraphics());

gsquare567 · **Posted:** Mon Apr 14, 2008 9:17 am

i love you

three0s · **Posted:** Mon May 21, 2012 8:15 pm

OneOffDriveByPoster @ Thu Apr 10, 2008 11:42 am wrote:

The repaint() will not call paint() until after you are finished your random walking loop. IIRC the callbacks are called from the same thread so doRandomWalk() and paint() will not run at the same time (unless if one calls the other).

A bad solution (force paint)

Java:

frame.paint(frame.getGraphics());

Thanks.
The bad solution is really a good solution in terms of making the program work.

md · **Posted:** Tue May 22, 2012 6:18 pm

The better solution would be to use a Swing timer in order to call doRandomWalk() which would perform one random step, draw, and then return.

It is usually a bad idea to perform long running calculations or attempt to implement your own frame-rate stuff in the Swing UI thread.

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