import java.awt.$*$;

import java.awt.event.$*$;

import javax.swing.$*$;

class Ball $\{$

static int defaultDiameter $=10$;

static Color defaultColor $=$ Color.white;

static Rectangle defaultBox $=$ new Rectangle$(0,0,100,100)$;

private int x$,$ y;

private int dx$,$ dy;

private int diameter;

private Color color;

private Rectangle box;

public Ball$($ int x$0,$ int y$0,$ int dx$0,$ int dy$0)\{$

x $=$ x$0$;

y $=$ y$0$;

dx $=$ dx$0$;

dy $=$ dy$0$;

color $=$ defaultColor;

diameter $=$ defaultDiameter;

$\}$

public void setColor$($ Color c $)\{$

color $=$ c;

$\}$

public void setBoundingBox$($ Rectangle r $)\{$

box $=$ r;

$\}$

public void paint$($ Graphics g $)\{$

g$.$setColor$($ color $)$;

g$.$fillOval$($ x$,$ y$,$ diameter, diameter $)$;

$\}$

void constrain$()\{$

int x$0=$ box.x;

int y$0=$ box.y;

int x$1=$ x$0+$ box.width $-$ diameter;

int y$1=$ y$0+$ box.height $-$ diameter;

if $($x $<$ x$0)\{$

dx $=$ Math.abs$($dx$)$;

$\}$

if $($x $>$ x$1)\{$

dx $=-$Math.abs$($dx$)$;

$\}$

if $($y $<$ y$0)\{$

dy $=$ Math.abs$($dy$)$;

$\}$

if $($y $>$ y$1)\{$

dy $=-$Math.abs$($dy$)$;

$\}$

$\}$

public void action$()\{$

x $=$ x $+$ dx;

y $=$ y $+$ dy;

constrain$()$;

$\}$

$\}$

class BallPanel extends JPanel implements ActionListener $\{$

private int width, height;

private Ball ball;

private Timer timer $=$ new Timer$(50,$ this$)$;

public BallPanel $($int width, int height$)\{$

this.width $=$ width;

this.height $=$ height;

ball $=$ new Ball$($ width $/10,$ height $/5,5,5)$;

ball.setBoundingBox$($ new Rectangle$(0,0,$ width, height $))$;

timer.start$()$;

$\}$

public void paintComponent$($ Graphics g $)\{$

g$.$setColor$($ Color.black $)$;

g$.$fillRect$(0,0,$ width, height $)$;

ball.paint$($ g $)$;

$\}$

public void actionPerformed$($ActionEvent e$)\{$

if$($width $!=$ getWidth$()||$ height $!=$ getHeight$())$

wasResized$($getWidth$(),$getHeight$())$;

ball.action$()$;

repaint$()$;

$\}$

public void wasResized$($ int newWidth, int newHeight $)\{$

width $=$ newWidth;

height $=$ newHeight;

$\}$

$\}$

class BallWorld extends JFrame $\{$

private BallPanel panel $=$ new BallPanel $(180,180)$;

public BallWorld $()\{$

Container c $=$ getContentPane$()$;

c$.$add$($panel$,$ BorderLayout.CENTER$)$;

setSize$(200,200)$;

setLocation$(100,100)$;

setVisible$($true$)$;

setDefaultCloseOperation$($EXIT$\_$ON$\_$CLOSE$)$;

$\}$

public static void main$($String args$[])\{$

BallWorld world $=$ new BallWorld$()$;

$\}$

$\}$