Transcript Threads and Media

Threads and Media
Chapter 8 - Lecture Slides
(c) 2008 E.S.Boese All Rights Reserved.
1
Threads

Multi-processing: 2 or more things occurring at the same time

When we run a program, a single thread automatically starts
to run the program.

To run two or more things simultaneously, we need to create a
second (or more) thread(s).

Ideal for slideshows, progress bars, animation, game
programming


For example, if we want to perform a slideshow while the user
is typing inside a, we need to use a separate thread for the
slideshow. JTextArea
If we didn't use a second thread, the applet would hang while
we ran through the code for the slideshow.
(c) 2008 E.S.Boese All Rights Reserved.
2
Threads – steps to make it work

There are four steps to get Thread to work:
1. The class needs to implement the Runnable interface.
implements Runnable
2. Create a Thread
Thread runner;
runner = new Thread( this );
3. Start the Thread
runner.start( );
4. Create a method named run
When we use Threads we
put the code inside the run
method.
public void run( )
{
}
(c) 2008 E.S.Boese All Rights Reserved.
3
run( ) method

Code goes inside the run method.
Usually we want the code to loop. We can set up the loop as an infinite loop.
public void run( )
{
while( true )
{
// code
}
}

infinite loop –
always true!
Use the method sleep in the Thread class to simulate a delay:
(This is the proper way to delay, unlike the for loop we used earlier in the book)
Thread.sleep( delayInMilliseconds );
OR
thread.sleep( delayInMilliseconds );

// thread variable
To use the sleep method, we need to put it within a try ... catch block to catch any
exceptions (errors) that may may occur
(usually put the try...catch around the while(true) loop):
try {
Thread.sleep( delayInMiliseconds );
} catch( Exception exc ) { }
(c) 2008 E.S.Boese All Rights Reserved.
4
Applet methods
Method Header
Description
public void init( )
Initialize our applet; called only once
public void start( )
Starts our applet running; start up necessary threads
public void stop( )
Applet is no longer being displayed; stop our threads from
running
(c) 2008 E.S.Boese All Rights Reserved.
5
Examples

Slideshow inside main applet class


see Slideshow.java
Slideshow in a separate class

see Slides.java and SlidesApplet.java
Animation Example

Animation is done by redrawing


see Wink.java and Smile.java
See AnimateThreads.java
(c) 2008 E.S.Boese All Rights Reserved.
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Game play - process
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Game play – offscreen images
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MediaTracker


Use for loading images and sound files
before the applet starts
Ensures everything is loaded properly before
the applet runs

Prevents empty screens or missing
graphics/media
(c) 2008 E.S.Boese All Rights Reserved.
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MediaTracker
import java.awt.*;
import javax.swing.*;
public class MediaTrackerEx extends JApplet
{
Image one, two, three, four;
MediaTracker imgTracker;
public void init()
{
loadImages();
}
public void start()
{
try
{
imgTracker.waitForAll();
}catch (Exception e)
{ }
}
public void loadImages()
{
one = getImage(getCodeBase(), "one.gif");
two = getImage(getCodeBase(), "two.gif");
three = getImage(getCodeBase(), "three.gif");
four = getImage(getCodeBase(), "four.gif");
imgTracker.addImage(one, 1);
imgTracker.addImage(two, 2);
imgTracker.addImage(three, 3);
imgTracker.addImage(four, 4);
}
}
(c) 2008 E.S.Boese All Rights Reserved.
10
Audio
(c) 2008 E.S.Boese All Rights Reserved.
11
Audio Files

Java can play the following audio types:





.au (Sun Audio)
.wav (Windows Wave)
.aif or .aiff (Macintosh AIFF)
.mid (Musical Instrument Digital Interface (MIDI)
.rmf
Note: wav files from your
CDs are HUGE! Won’t run
well – only use small WAV
files
Note: mp3 is NOT supported
in the Java API. However,
There are libraries you can
download and use
Audio
getCodeBase( )
works same for
images as audio
files
AudioClip clip;
clip = getAudioClip( getCodeBase( ), audioFilename );
clip.play( );

There are three methods we can call on our AudioClip

play

loop

stop
play the sound file once through
play the sound file continually
stop playing the file
Audio
import java.awt.*;
import java.applet.*;
import javax.swing.*;
public class AudioPlay extends JApplet
{
String audioFilename = "mySounds.mid";
AudioClip ac;
public void init( )
{
ac = getAudioClip( getCodeBase( ), audioFilename );
ac.play( );
}
}
Audio
To have sound clip loop:
 get an AudioClip
 call the loop( ) method
import java.awt.*;
import java.applet.*;
import javax.swing.*;
public class AudioPlay extends JApplet
{
String audioFilename = "mySounds.mid";
AudioClip ac;
public void init( )
{
ac = getAudioClip( getCodeBase( ), audioFilename );
ac.loop( );
}
}
Audio: Need for stop( )

See Example

Each button starts an audio file playing

If the previous one isn’t stopped first,
then the new one plays on TOP of the other one

This is usually not desired
However, some applications want this
technique
(see example of Singing Horses on Internet at:
http://svt.se/hogafflahage/hogafflaHage_site/Kor/hestekor.swf
stop method
Stop playing audio when
user leaves the applet:
 Write a stop method
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import javax.swing.*;
public class LoopAudio extends JApplet
{
String audioFilename = "happyDaze.wav";
AudioClip ac;
public void init( )
{
ac = getAudioClip( getCodeBase( ), audioFilename );
ac.loop( );
// loop instead of play
}
public void stop( )
{
// can't stop it if it isn't running, check first
if( ac != null )
ac.stop( );
}
}
Timers
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Timers

Timers are useful for repeating steps at particular intervals.
 Examples: progress bars, custom clocks and timed animation,
tooltips, blinking cursor

Timers are based on event processing,
 Important that the code to be run from a Timer event can be
executed quickly to enable the system to handle the next event.
(Threads do not have this limitation and therefore are ideal for
more time-intensive code processing).

Create a Timer object by specifying the delay count in
milliseconds and the listener for the ActionEvent:
Timer timer;
timer = new Timer( delay, this );
(c) 2008 E.S.Boese All Rights Reserved.
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Timers

Similar to threads, we then need to start the timer:
timer.start( );

After the delay in milliseconds, the actionPerformed method is
called. Therefore, just like when we listen for events on buttons, we
need to implement the ActionListener.
public void actionPerformed( ActionEvent ae )
{
Object src = ae.getSource( );
if ( src instanceof Timer )
// do something since Timer expired
else if ( src instanceof JButton )
// do something based on a button click
}
(c) 2008 E.S.Boese All Rights Reserved.
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Timers

There are five steps to get Timer to work:
1. Import the package to handle ActionEvent events:
import java.awt.event.*;
2. Specify that we're listening for events:
public class xyz extends JApplet implements ActionListener
3. Create a Timer object
Timer timer;
timer = new Timer( delay, this );
4. Start the timer:
timer.start( );
5. Add an actionPerformed method:
public void actionPerformed( ActionEvent ae )
{
Object src = actionEvent.getSource( );
if ( src instanceof Timer )
...
else if ( src instanceof JButton )
...
}
6. (Optional) Stop the Timer
timer.stop( );
(c) 2008 E.S.Boese All Rights Reserved.
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TimedClock Example
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class TimedClock extends JApplet implements ActionListener
{
JLabel countdown;
int count = 10;
Timer timer;
int DELAY = 800;
// delay in miliseconds
public void init( )
{
setLayout( new FlowLayout( ) );
countdown = new JLabel( String.valueOf( count ) );
countdown.setFont( new Font( "Serif", Font.BOLD, 46 ) );
add( countdown );
timer = new Timer( DELAY, this );
timer.start( );
}
public void actionPerformed( ActionEvent ae )
{
Object src = ae.getSource( );
if ( src == timer && count > 0 )
{
count = count - 1;
countdown.setText( String.valueOf( count ) );
}
if ( count == 0 )
countdown.setText( "Blast-off!" );
}
}
(c) 2008 E.S.Boese All Rights Reserved.
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Summary




Threads
MediaTracker
Audio
Timers
(c) 2008 E.S.Boese All Rights Reserved.
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