Swing Hacks

Provide Audio Controls During Playback #78

Chapter 10, Audio

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401

HACK

Of course, Sun could just go and actually implement getLevel( )…wouldn’t

that be nice?

H A C K

#78

Provide Audio Controls During Playback Hack #78

Let your users take control of JavaSound playback.

To complete this set of JavaSound-related hacks, why not give the user the

opportunity to control the sound as it plays? JavaSound provides a very

dynamic means of getting at controls like gain and pan (more commonly

thought of as volume and balance) through a discovery mechanism that you

can use to support any kind of control that might exist, even a control you

know nothing about.

On the other hand, JavaSound presents a control not as a GUI widget, but

just as an object that can affect the behavior of a

Line. This hack will help

you provide the GUI side.

The

Control class simply defines a getType( ) and toString( ) method.

What’s more interesting is its subclasses, each of which defines a different

kind of control:

BooleanControl

Controls a value that can be either true or false

EnumControl

Controls a value that can be one of n known values

FloatControl

Controls a value that is expressed as a floating-point number

CompoundControl

Controls multiple properties, and itself contains multiple controls

You can get the

Controls supported by your Line simply by calling Line.

getControls( )

, which returns an array of Controls. You can also ask for a

specific control by using a constant of the

Control.Type subclass, such as

BooleanControl.Type.MUTE or FloatControl.Type.MASTER_GAIN. Pass this con-

stant to

Line.isControlSupported( ) to see if the control is available for the

given line, and then get the control object with

Line.getControl( ).

If you look at the subclasses of

Control, you’ll see that each provides getter

and setter methods appropriate to its data type.

BooleanControl, for exam-

ple, has a

getValue( ) that returns a boolean and a setValue( ) that takes a

boolean. FloatControl has similar methods that work with floats. Each also

provides a number of what might be called “verbiage methods” that provide

text for building a GUI. For example,

FloatControl offers label names for its

minimum, maximum, and middle values, and another that describes the