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TargetDataLine (Java 2 Platform SE 5.0) - JDK 5 Documentation v1.5.0, Java 2 SDK 英文文档

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javax.sound.sampled
Interface TargetDataLine

All Superinterfaces:
DataLine, Line
public interface TargetDataLine
extends DataLine

A target data line is a type of DataLine from which audio data can be read. The most common example is a data line that gets its data from an audio capture device. (The device is implemented as a mixer that writes to the target data line.)

Note that the naming convention for this interface reflects the relationship between the line and its mixer. From the perspective of an application, a target data line may act as a source for audio data.

The target data line can be obtained from a mixer by invoking the getLine method of Mixer with an appropriate DataLine.Info object.

The TargetDataLine interface provides a method for reading the captured data from the target data line's buffer.Applications that record audio should read data from the target data line quickly enough to keep the buffer from overflowing, which could cause discontinuities in the captured data that are perceived as clicks. Applications can use the available method defined in the DataLine interface to determine the amount of data currently queued in the data line's buffer. If the buffer does overflow, the oldest queued data is discarded and replaced by new data.

Since:
1.3
See Also:
Mixer, DataLine, SourceDataLine

Nested Class Summary
 
Nested classes/interfaces inherited from interface javax.sound.sampled.DataLine
DataLine.Info
 
Method Summary
 void open(AudioFormat format)
          Opens the line with the specified format, causing the line to acquire any required system resources and become operational.
 void open(AudioFormat format, int bufferSize)
          Opens the line with the specified format and requested buffer size, causing the line to acquire any required system resources and become operational.
 int read(byte[] b, int off, int len)
          Reads audio data from the data line's input buffer.
 
Methods inherited from interface javax.sound.sampled.DataLine
available, drain, flush, getBufferSize, getFormat, getFramePosition, getLevel, getLongFramePosition, getMicrosecondPosition, isActive, isRunning, start, stop
 
Methods inherited from interface javax.sound.sampled.Line
addLineListener, close, getControl, getControls, getLineInfo, isControlSupported, isOpen, open, removeLineListener
 

Method Detail

open

void open(AudioFormat format,
          int bufferSize)
          throws LineUnavailableException
Opens the line with the specified format and requested buffer size, causing the line to acquire any required system resources and become operational.

The buffer size is specified in bytes, but must represent an integral number of sample frames. Invoking this method with a requested buffer size that does not meet this requirement may result in an IllegalArgumentException. The actual buffer size for the open line may differ from the requested buffer size. The value actually set may be queried by subsequently calling DataLine.getBufferSize()

If this operation succeeds, the line is marked as open, and an OPEN event is dispatched to the line's listeners.

Invoking this method on a line that is already open is illegal and may result in an IllegalStateException.

Some lines, once closed, cannot be reopened. Attempts to reopen such a line will always result in a LineUnavailableException.

Parameters:
format - the desired audio format
bufferSize - the desired buffer size, in bytes.
Throws:
LineUnavailableException - if the line cannot be opened due to resource restrictions
IllegalArgumentException - if the buffer size does not represent an integral number of sample frames, or if format is not fully specified or invalid
IllegalStateException - if the line is already open
SecurityException - if the line cannot be opened due to security restrictions
See Also:
open(AudioFormat), Line.open(), Line.close(), Line.isOpen(), LineEvent

open

void open(AudioFormat format)
          throws LineUnavailableException
Opens the line with the specified format, causing the line to acquire any required system resources and become operational.

The implementation chooses a buffer size, which is measured in bytes but which encompasses an integral number of sample frames. The buffer size that the system has chosen may be queried by subsequently calling DataLine.getBufferSize()

If this operation succeeds, the line is marked as open, and an OPEN event is dispatched to the line's listeners.

Invoking this method on a line that is already open is illegal and may result in an IllegalStateException.

Some lines, once closed, cannot be reopened. Attempts to reopen such a line will always result in a LineUnavailableException.

Parameters:
format - the desired audio format
Throws:
LineUnavailableException - if the line cannot be opened due to resource restrictions
IllegalArgumentException - if format is not fully specified or invalid
IllegalStateException - if the line is already open
SecurityException - if the line cannot be opened due to security restrictions
See Also:
open(AudioFormat, int), Line.open(), Line.close(), Line.isOpen(), LineEvent

read

int read(byte[] b,
         int off,
         int len)
Reads audio data from the data line's input buffer. The requested number of bytes is read into the specified array, starting at the specified offset into the array in bytes. This method blocks until the requested amount of data has been read. However, if the data line is closed, stopped, drained, or flushed before the requested amount has been read, the method no longer blocks, but returns the number of bytes read thus far.

The number of bytes that can be read without blocking can be ascertained using the available method of the DataLine interface. (While it is guaranteed that this number of bytes can be read without blocking, there is no guarantee that attempts to read additional data will block.)

The number of bytes to be read must represent an integral number of sample frames, such that:

[ bytes read ] % [frame size in bytes ] == 0

The return value will always meet this requirement. A request to read a number of bytes representing a non-integral number of sample frames cannot be fulfilled and may result in an IllegalArgumentException.

Parameters:
b - a byte array that will contain the requested input data when this method returns
off - the offset from the beginning of the array, in bytes
len - the requested number of bytes to read
Returns:
the number of bytes actually read
Throws:
IllegalArgumentException - if the requested number of bytes does not represent an integral number of sample frames. or if len is negative.
ArrayIndexOutOfBoundsException - if off is negative, or off+len is greater than the length of the array b.
See Also:
SourceDataLine.write(byte[], int, int), DataLine.available()
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JavaTM 2 Platform
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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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