Swing Hacks

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Chapter 10, Audio

#70 Play a Sound in an Applet

HACK

The last three buttons—Play, Stop, and Loop—are handled trivially in

actionPerformed( ) with calls to the Applet methods play( ), stop( ), and

loop( )

, respectively.

I’ve also provided a

main( )

method here. Applets don’t need them, but since

an applet is just a

JPanel

, why not just put it in a

JFrame

and run it, right?

What’s the worst that could happen?

No Browser, No Sound

Since there’s a main( ) method, just type java AppletAudio on the command

line and the applet will come up in its own frame, as seen in Figure 10-1.

Click the File button and choose a file to have its URL placed in the field.

Now, click Play.

Nothing happens. If you have an output console, you should see something

like:

java.lang.NullPointerException

at java.applet.Applet.getAppletContext(Applet.java:171)

at java.applet.Applet.getAudioClip(Applet.java:279)

at AppletSound.actionPerformed(AppletSound.java:71)

at javax.swing.AbstractButton.fireActionPerformed(

AbstractButton.java:1819)

...

I’ll save you the time of typing a URL by hand and hitting Load; the same

thing happens.

What’s happening is that the implicit call to

getAppletContext( ) is failing

because there is no applet context; i.e., the environment in which the applet

is executed. An applet expects to run in a browser or something similar that

provides access to cached images and sounds and the ability to get docu-

ments ...