Java How to Program Fourth Edition - DCC

1282 Java Media Framework and Java Sound (on CD) Chapter 22
portedAudioFileException if the specified sound file is a non-audio file or if it
contains a format that is not supported by Java Sound.
Next the program must provide a line through which audio data can be processed. Line
52 invokes method loadClip (lines 57–106) to open a Clip line and load the audio
stream for playback. Line 81 invokes AudioSystem static method getLine to
obtain a Clip line for audio playback. Method getLine requires a Line.Info object
as an argument, to specify the attributes of the line that the AudioSystem should return.
The line must be able to process audio clips of all supported sampled audio formats, so the
DataLine.Info object must specify a Clip data line and a general encoding format. A
buffer range should also be specified so the program can determine the best buffer size. The
DataLine.Info constructor receives four arguments. The first two are the format (of
type AudioFormat.Encoding) into which the program should convert the audio data
and the AudioFormat of the audio source. The AudioFormat sets the format supported
by the line, according to the audio format of the stream. Line 63 obtains the Audio-
Format of the AudioInputStream, which contains format specifications that the
underlying system uses to translate the data into sounds. Lines 68–69 call AudioSystem
method getTargetFormats to obtain an array of the supported AudioFormats. The
third argument of the DataLine.Info constructor, which specifies the minimum buffer
size, is set to the number of bytes in each frame of the audio stream. Line 70 invokes
AudioFormat method getFrameSize to obtain the size of each frame in the audio
stream. The maximum buffer size should be equivalent to two frames of the audio stream
(line 71). Using the DataLine.Info object, line 74 checks if the underlying audio
system supports the specified line. If it does, line 81 obtains the line from the audio system.
When an audio clip starts playing and when it finishes, the program needs to be alerted.
Line 84 registers a LineListener for the Clip’s LineEvents. If a LineEvent
occurs, the program calls LineListener method update (lines 115–133) to process it.
The four LineEvent types, as defined in class LineEvent.Type, are OPEN, CLOSE,
START and STOP. When the event type is LineEvent.Type.STOP and variable
replay is false, line 120 calls ClipPlayer’s close method (lines 142–148) to stop
audio playback and close the Clip. All audio resources obtained previously by the Clip
are released when audio playback stops. When the event type is
LineEvent.Type.STOP and variable replay is true, line 131 calls Clip method
loop with parameter Clip.LOOP_CONTINUOUSLY, causing the Clip to loop until the
user terminates the application. Invoking method stop of interface Clip stops data
activity in the Line. Invoking method start resumes data activity.
Once the program finishes validating the Clip, line 87 calls Clip method open with
the AudioInputStream soundStream as an argument. The Clip obtains the system
resources required for audio playback. AudioSystem method getLine and Clip
method open throw LineUnavailableExceptions if another application is using
the requested audio resource. Clip method open also throws an IOException if the
Clip cannot read the specified AudioInputStream. When the test program (Fig. 22.6)
calls ClipPlayer method play (lines 109–112), the Clip method start begins
audio playback.
Class ClipPlayerTest (Fig. 22.6) enables users to specify an audio file to play by
clicking the Open Audio Clip button. When users click the button, method action-
Performed (lines 37–58) prompts an audio file name and location (line 39) and creates