(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 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. 2

(c) 2008 E.S.Boese All Rights Reserved. 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. 3

(c) 2008 E.S.Boese All Rights Reserved. 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 ); 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 ) { } infinite loop – always true! 4

Applet methods Method HeaderDescription 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 6

Game play - process (c) 2008 E.S.Boese All Rights Reserved. 7

Game play – offscreen images (c) 2008 E.S.Boese All Rights Reserved. 8

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 9

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

(c) 2008 E.S.Boese All Rights Reserved. Audio 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: 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( ); }

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:

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( ); } Stop playing audio when user leaves the applet: Write a stop method

(c) 2008 E.S.Boese All Rights Reserved. Timers 18

(c) 2008 E.S.Boese All Rights Reserved. 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 ); 19

(c) 2008 E.S.Boese All Rights Reserved. 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 } 20

(c) 2008 E.S.Boese All Rights Reserved. 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( ); 21

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. 22

(c) 2008 E.S.Boese All Rights Reserved. Summary Threads MediaTracker Audio Timers 23