Simulations, pixels and repainting

Question

Currently im trying to simulate a model of a few thousand objects (existing as species) and moving hunting etc as defined by code that i've already tested to work fine. My problem however comes to the GUI side of things, how for instance do you draw just 1 pixel? Does this become a Rectangle I need to fill which is 1*1 pixel in size? Or is there some kind of functionality to paint just one single pixel.
Following from this is my use of the repaint method. How can I go about 'repainting' a window without having to make it invisible and just draw a whole new one? I read the API referring to how JLabel's inherit repaint from about 30 different locations and decided to test out the simplest one where I pass the label.repaint(label), after having change the foreground, background, etc but it doesn't actually repaint it.
If someone could literally give me the code to draw a dot and then show me how they would move the dot to the right for instance (covering up the dot's tracks with the background colour) it would be massively appreciated.

Answer 1

Here's a short sample app that will show you the basics of one way to do this.
package com.sun.java.forums;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.List;
import java.util.Vector;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
public class LifePanel extends JPanel
     List<Point> pointsToPaint;
     public LifePanel()
          super();
          pointsToPaint = new Vector<Point>();
     public void setPoints(List<Point> points)
          this.pointsToPaint = points;
     @Override
     protected void paintComponent(Graphics g)
          Graphics2D g2d = (Graphics2D)g;
          // fill in the background
          g2d.setColor(getBackground());
          g2d.fill(g2d.getClip());
          // fill in the pixels
          g2d.setColor(getForeground());
          for (Point p: pointsToPaint)
               g2d.fillRect(p.x, p.y, 1, 1);
     public static void main(String args[])
          JFrame f = new JFrame();
          f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          f.setLayout(new BorderLayout());
          final LifePanel lp = new LifePanel();
          lp.setBackground(Color.WHITE);
          lp.setForeground(Color.BLACK);
          final Point singlePoint = new Point(0,0);
          List<Point> points = new Vector<Point>();
          points.add(singlePoint);
          lp.setPoints(points);
          f.add(lp,BorderLayout.CENTER);
          f.setSize(400,400);
          f.setVisible(true);
          // move the point every second
          Timer timer = new Timer(250,new ActionListener()
               public void actionPerformed(ActionEvent ae)
                    // move the point 1 to the right and 1 down
                    singlePoint.translate(1, 1);
                    lp.repaint();
          timer.setRepeats(true);
          timer.start();
}This will create a 400 by 400 white area with a little black pixel on it. 4 times per second, the pixel will move to the southeast.
Your app will have much more interesting motion of points, I hope.