Increasing lenght per second

Question

Hi,i want to create an applet which will contain a rectangle.The rectangle will be filled with any color and its lenght will increase by 1 cm per second.I know that i have to use threads to achieve this but when i try it something seems to go wrong,can anybody help me?

Answer 1

maybe this is what you're looking for?!
import java.applet.*;
import java.awt.*;
import java.util.*;
class Dot {
     public int x,y;
     public float xdir,ydir;
     public Dot(int x,int y,float xdir,float ydir) {
          this.x = x;
          this.y = y;
          this.xdir = xdir;
          this.ydir = ydir;
public class Rect extends Applet implements Runnable {
     Dot dot[];
     Image buffer;
     int w,h,scale;
     final float GRAVITY = 0.1f,MAX_XDIR = -1.0f,MAX_YDIR = -8.0f,MIN_YDIR = 1.0f;
     public void init() {
          w = getSize().width;
          h = getSize().height;
          scale = 100;
          buffer = createImage(w,h);
          initRect();
          new Thread(this).start();
     protected void initRect() {
          Vector v = new Vector(0);
          int x,y;
          for (y = scale;y < h-scale;y++) {
               if (y == scale || y == h-scale-1) {
                    for (x = scale;x < w-scale;x++) {
                         v.addElement(new Dot(x,y,MAX_XDIR,MIN_YDIR));
               else {
                    v.addElement(new Dot(scale,y,MAX_XDIR,MIN_YDIR));
                    v.addElement(new Dot(w-scale-1,y,MAX_XDIR,MIN_YDIR));
          dot = new Dot[v.size()];
          for (x = 0;x < dot.length;x++) {
               dot[x] = (Dot)v.elementAt(x);
     public void run() {
          while (true) {
               for (int j = 0;j < dot.length;j++) {
                    dot[j].y+=(int)dot[j].ydir;
                    dot[j].x+=(int)dot[j].xdir;
                    dot[j].ydir+=GRAVITY;
                    if (dot[j].x < 0) {
                         dot[j].x = 0;
                         dot[j].xdir*=-1.0f;
                    if (dot[j].x > w) {
                         dot[j].x = w;
                         dot[j].xdir*=-1.0f;
                    if (dot[j].y >= h) {
                         dot[j].y = h;
                         dot[j].ydir = MAX_YDIR;
               Graphics g = getGraphics();
               if (g != null) paint(g);
               else repaint();
               try {
                    Thread.sleep(10);
               catch (InterruptedException e) {
                    break;
     public void paint(Graphics g) {
          Graphics gfx = buffer.getGraphics();
          gfx.setColor(Color.white);
          gfx.fillRect(0,0,w,h);
          gfx.setColor(Color.black);
          for (int j = 0;j < dot.length;j++) {
               gfx.drawRect(dot[j].x,dot[j].y,1,1);
          g.drawImage(buffer,0,0,null);
     public void update(Graphics g) {
          paint(g);
}lol.. have fun with that flexible little bugger... (if you're too lazy to compile, just view it here)