(c) 2008 e.s.boese all rights reserved. threads and media chapter 8 - lecture slides 1

(c) 2008 E.S.Boese All Rights Reserved.

Threads and Media

Chapter 8 - Lecture Slides

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.

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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

public void run( ){}

When we use Threads we put the code inside the run

method.

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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}

}

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 );ORthread.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 ) { }

infinite loop – always true!

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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 is done by redrawing see Wink.java and Smile.java See AnimateThreads.java

Animation Example

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Game play - process


Game play – offscreen images



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

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MediaTrackerimport 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);

} }



Audio

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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: mp3 is NOT supported in the Java API. However, There are libraries you can

download and use

Note: wav files from your CDs are HUGE! Won’t run well – only use small WAV

files

Audio

AudioClip clip;

clip = getAudioClip( getCodeBase( ), audioFilename );

clip.play( );

There are three methods we can call on our AudioClip play play the sound file once through loop play the sound file continually stop stop playing the file

getCodeBase( ) works same for images as audio

files

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( );

}}

AudioTo 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

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 firstif( ac != null )

ac.stop( ); }

}

Stop playing audio when user leaves the applet:

Write a stop method


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 );

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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 }

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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 Timertimer.stop( );

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TimedClock Exampleimport 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!" ); }}



Summary

Threads MediaTracker Audio Timers

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(c) 2008 e.s.boese all rights reserved. threads and media chapter 8 - lecture slides 1

Documents

thread thread runnerrunner

thread class

run method

separate thread

method sleep

sleep method

new thread

single thread