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

public class Space extends JFrame {
  int xLim = 500, yLim = 500;
  Vector balls = new Vector();

  public static void main(String[] args) {
    new Space();
  }

  Space() {
    setSize(xLim, yLim);
    setVisible(true);
    addKeyListener(new L());
  }

  synchronized void addBall() {
    balls.add(new Ball());
    setTitle("Antal bollar: " + balls.size());
  }

  synchronized void removeBall(Ball ball) {
    balls.remove(ball);
    setTitle("Antal bollar: " + balls.size());
  }

  synchronized void pauseBalls() {
    for(int i = 0; i < balls.size(); i++) {
      if(((Ball)balls.elementAt(i)).active) {
        ((Ball)balls.elementAt(i)).active = false;
      } else {
        ((Ball)balls.elementAt(i)).active = true;
      }
    }
  }

  class L extends KeyAdapter {
    public void keyPressed(KeyEvent e) {
      if(e.getKeyChar() == '+') addBall();
      if(e.getKeyChar() == 'p') pauseBalls();
    }
  }

  class Ball extends Thread {
    boolean alive = true, active = true;
    Random rnd = new Random();
    int eMax= 500, e = rnd.nextInt(eMax), rMax = xLim / 2, r = rnd.nextInt(rMax), dr = 1, x = xLim / 2 - r / 2, y = yLim / 2 - r / 2, dx, dy, dMax = 3, ddx = 1, ddy = 1, gr = 5;

    Ball() {
      if(rnd.nextBoolean()) ddx = -1;
      dx = rnd.nextInt(dMax) * ddx;
      if(rnd.nextBoolean()) ddy = -1;
      dy = rnd.nextInt(dMax) * ddy;

      start();
    }

    public void run() {
      while(alive) {
        while(active) {
          Graphics g = getGraphics();
          g.setColor(getBackground());
          g.fillOval(x, y, r, r);

          if((x <= 0) || (x >= xLim - r)) { dx *= -1; r -= dr * eMax / e; }
          if((y <= 30) || (y >= yLim - r)) { dy *= -1; r -= dr * eMax / e; }

          if((r <= 0) || (e <= 0)) {
            active = false;
            alive = false;
            removeBall(this);
          } else {
            e -= 1;
            int rChange = dr * eMax / e;
            r -= rChange; if(r < 0 ) r = 0;
            x += dx + rChange / 2;
            y += dy + rChange / 2; y += gr * (eMax - e) / eMax;

            g.setColor(new Color(255, 255, 255 - 255 * r / rMax));
            g.fillOval(x, y, r, r);
          }
          try { sleep(500000 / (r * r)); } catch(Exception e) {}
        }
        try { sleep(100); } catch(Exception e) {}
      }
    }
  }
}