Multimedia in Java

1
Multimedia in Java

• Weve already spent a good deal of time dealing
  with computer graphics, so we now focus on
  animation and sound
• To perform animation, we basically want to call
  repaint( ) every few milliseconds
• how does our program know when a few milliseconds
  elapse?
• there is a Timer class available set it for 20
  milliseconds and every 20 milliseconds, the Timer
  generates an ActionEvent
• we them implement an ActionListener to handle the
  event through an actionPerformed method
• in the case of animation, the actionPerformed
  method may only have to add 1 to the x or y
  coordinate of the item we are drawing, and then
  call repaint( )
• To handle sound, we have to cheat in a way
  because sound is only available through Applets
  or through a special IO library written by Sun,
  we will so both approaches

2
Timer class

• A Timer object is instantiated by
• Timer t new Timer(duration, handler)
• duration is the time (in milliseconds) that
  elapses between Timer-generated events, such as
  20 or 50
• handler is the object that handles the
  Timer-generated events we will usually just use
  this and implement actionPerformed in our class
  whenever possible (this may not be easy if we
  also implement an ActionListener in this class to
  handle JButtons
• import java.awt.event.
• add implements ActionListener to our class
  header
• instantiate the Timer as t new Timer(10, this)
  but use whatever value you want for the
  duration, 10 or 20 would be adequate for most
  applications
• start the timer by using t.start( )
• if we need to stop the timer, we use t.stop( )
• Thats about all there is to it!

3
TimerSkeleton
import javax.swing. import java.awt.event. pu
blic class TimerSkeleton implements
ActionListener private Timer t // other
instance data go here as needed public
TimerSkeleton( ) t new Timer(10,
this) t.start( ) // other initialization
operations go here as needed // other
methods go here as needed public void
actionPerformed(ActionEvent e) // whatever
you want to happen when the Timer pulses go
here
4
What Should actionPerformed Do?

• This depends on why you are using a Timer
• to move an object in a Graphics panel (e.g., a
  ball)
• alter the x and y coordinates and call repaint( )
• for a Game
• calculate where game objects (say a spacecraft or
  a missile) have moved and redraw them
• this may require the user of an array of x and an
  array of y values to store the various objects,
  or multiple variables such as myX, myY, yourX,
  yourY, or both (the arrays might store the X and
  Y coordinates of missiles launched from one to
  the other)
• for Animation
• if our item being drawn is represented by an
  array of different figures
• then just increment the array index and repaint(
  )
• we will see an example of a StickFigure, but this
  could also be done by having a series of jpg or
  gif files all pre-loaded into an array of Images

5
Moving a Game Object

• Imagine that your class draws on a JPanel an
  ImageIcon (say of a spaceship)
• Currently, the spaceship is located at
  coordinates x, y
• The following actionPerformed method will
  randomly move the spaceship on the screen
• This assumes that x and y are class variables so
  that you could do g.drawImage(image, x, y, this)
  in repaint( )

public void actionPerformed(ActionEvent e)
int dx generator.nextInt( ) 2 //
generate a from -1 to 1 int dy
generator.nextInt( ) 2 // generate a from
-1 to 1 x dx // move the piece in a
random x direction y dy // move the
piece in a random y direction repaint(
) // assume repaint does drawImage at x, y
6
Full Example Code
public TimerExample( ) t new Timer(10,
this) t.start( ) x 150 y 150
repaint( ) public void actionPerformed(ActionEv
ent ev) int distanceX generator.nextInt( ))
2 int distanceY generator.nextInt( ))
2 x distanceX y distanceY repaint(
) public void paintComponent(Graphics
g) super.paintComponent(g) g.setColor(Color.r
ed) g.fillOval(x, y, 5, 5)
At each Timer Event, randomly move the object (a
red circle) up/down/left/right by 0 or 1
unit Note we could make it more realistic by
generating a random int from 1-9 and move it in
one of 8 directions or leave it stationary (1
upper left, or subtract 1 from x and y, 2
straight up, etc)
7
Handling Multiple ActionEvents
private static class ExamplePanel extends JPanel
implements ActionListener private Timer
t private JButton b public ExamplePanel(
) t new Timer(1000, this) t.start()
b new JButton("Button") b.addActionListen
er(this) add(b) public void
actionPerformed(ActionEvent e) if(e.getSour
ce( ) t) System.out.println("Timer
pulsed") else if(e.getSource( )
b) System.out.println("Button
pressed")
8
Moving Multiple Items

• How would a game like Asteroids work?
• We need to keep track of the ltx, ygt coordinates
  of multiple values, just like we did with our
  paint program
• So we create an array of x, y, dx and dy int
  values
• private int x, y, dx, dy // dx, dy velocity
  of x, y
• private int num // number of items in the arrays
• actionPerformed now manipulates all items in the
  array and paintComponent draws them all

If xi or yi reaches a boundary (0 or max
X/Y) then change dx or dy to be the opposite
(multiply by -1)
public void actionPerformed(ActionEvent e)
for(int i0iltnumi) xidxi
yidyi
9
Sound/Music

• Just as Java has a facility for displaying an
  image using the ImageIcon class, you can also
  play sounds/music
• This facility is only available through the
  Applet class or through an IO class created by
  Sun
• The harder way
• Import java.applet.
• Create a nested inner class that extends Applet,
  include an instance data of type AudioClip and in
  the Applet constructor, instantiate an Applet
  object
• aClip Applet.newAudioClip(getClass(
  ).getResource(filename))
• Add an accessor method to your Applet to return
  the audio clip
• The slightly easier way
• Import java.io. and sun.audio.
• Create objects of types InputStream and
  AudioStream and then tell the AudioPlayer class
  to play your AudioStream

10
AudioClip Example
import java.applet. // needed to generate an
AudioClip public class AudioExample2 public
static void main(String args) AClip a
new AClip() // create an Applet AudioClip c
a.getClip() // use the Applet to generate an
AudioClip c.play( ) // play the
AudioClip private static class AClip
extends Applet // Applet as an inner class
used to // generate AudioClip
objects private static AudioClip a
// Our AudioClip public AClip() //
constructor a Applet.newAudioClip(g
etClass( ).getResource("chimes.wav"))
// getClass( ) returns the file location of
this class // getResource returns the actual
item, in this case a wav file public
AudioClip getClip() // accessor
return a
11
Another Audio Example
import java.io. // use this to create an
InputStream import sun.audio. // another class
that can be used to play audio public class
AudioExample2 public static void main(String
args) try // create an
AudioStream of the wav file InputStream in
new FileInputStream("chimes.wav") AudioStream
as new AudioStream(in) // play the
AudioStream AudioPlayer.player.start(as)
// use the following instead to play the
wav file repeatedly in a continuous
loop //AudioData data as.getData() //Cont
inuousAudioDataStream cas // new
ContinuousAudioDataStream (data)
//AudioPlayer.player.start(cas)

catch(IOException ex) // any code here will be
used if trying the audio player doesnt
work!