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In the JavaApplet
package (java.applet
), theApplet
class and
AudioClip
interface provide basic support for playing sounds. Currently, the Java API supports only one sound format: 8 bit, µlaw, 8000 Hz, one-channel, Sun ".au" files. You can create these on a Sun workstation using the
audiotool
application. You can convert files from other sound formats using an audio format conversion program.
Below are the sound-relatedApplet
methods. The two-argument form of each method takes a base URL, which is usually returned by eithergetDocumentBase
orgetCodeBase
, and the location of the sound file relative to the base URL. You should use the code base for sounds that are integral to the applet. The document base is used for sounds specified by the applet user, such as through applet parameters.
getAudioClip(URL)
,getAudioClip(URL, String)
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- Return an object that implements the
AudioClip
interface.play(URL)
,play(URL, String)
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- Play the
AudioClip
corresponding to the specified URL.The
AudioClip
interface defines the following methods:
loop
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- Starts playing the clip repeatedly.
play
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- Plays the clip once.
stop
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- Stops the clip. Works with both looping and one-time sounds.
Here is an applet called SoundExample that illustrates a few things about sound. Note that, for instructional purposes, the applet adds up to 10 seconds to the load time for each sound. If the sounds were larger or the user's connection slower than ours, these delays might be realistic.
Note: Because some old browsers don't support 1.1, the above applet is a 1.0 version (here is the 1.0 code; here's the 1.1 code). To run the 1.1 version of the applet, go toexample-1dot1/SoundExample.html
. For more information about running applets, refer to About Our Examples.
The SoundExample applet provides an architecture for loading and playing multiple sounds in an applet. For this reason, it is more complex than necessary. Essentially, the sound loading and playing code boils down to this:
AudioClip onceClip, loopClip; onceClip = applet.getAudioClip(getCodeBase(), "bark.au"); loopClip = applet.getAudioClip(getCodeBase(), "train.au"); onceClip.play(); //Play it once. loopClip.loop(); //Start the sound loop. loopClip.stop(); //Stop the sound loop.
Since there's nothing more annoying than an applet
that continues to make noise
after you've left its page,
the SoundExample applet stops playing the continuously looping sound
when the user leaves the page,
and resumes playing it when the user comes back.
It does this by implementing its
stop
and
start
methods as follows:
public void stop() { //If one-time sound were long, we'd stop it here, too. //looping is a boolean instance variable that's initially //false. It's set to true when the "Start sound loop" button //is clicked and to false when the "Stop sound loop" or "Reload //sounds" button is clicked. if (looping) { loopClip.stop(); //Stop the sound loop. } } public void start() { if (looping) { loopClip.loop(); //Restart the sound loop. } }
The SoundExample applet features three classes:
Applet
subclass,
SoundExample
Hashtable
subclass,
SoundList
AudioClip
s.
This is overkill for this applet,
but if you were to write an applet that used lots of sound files,
a class like this would be useful.
Thread
subclass,
SoundLoader
AudioClip
in the background.
During the applet's initialization,
the applet preloads each sound by creating a SoundLoader
for it.
Preloading the sounds in a background thread (with SoundLoader
)
improves the perceived performance
by reducing the amount of time the user has to wait
to be able to interact with the applet.
It does this by reducing the amount of time
spent in the init
method.
If you simply called getAudioClip
in the applet's init
method,
it could take quite a while before getAudioClip
returned,
meaning that the applet couldn't perform the other statements
in its init
method,
and that the applet's start
wouldn't get called.
(For this SoundExample applet,
a delay in calling the start
method doesn't matter.)
Another advantage of loading the sounds in a background thread
is that it enables
the applet to respond appropriately (and immediately) to user input
that would normally cause a sound to play,
even if that sound hasn't been loaded yet.
If you simply use the Applet play
methods,
for example,
then the first time the user does something
to make the applet play a particular sound,
the applet's drawing and event handling are frozen
while the sound is loaded.
Instead, this applet detects that the sound hasn't been loaded yet
and responds appropriately.
This example is discussed in more detail in
Threads in Applets: Examples.
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