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.

@author
Kara Kytle
@version
1.20 03/12/19
@since
1.3
Obtains the number of bytes of data currently available to the application for processing in the data line's internal buffer. For a source data line, this is the amount of data that can be written to the buffer without blocking. For a target data line, this is the amount of data available to be read by the application. For a clip, this value is always 0 because the audio data is loaded into the buffer when the clip is opened, and persists without modification until the clip is closed.

Note that the units used are bytes, but will always correspond to an integral number of sample frames of audio data.

An application is guaranteed that a read or write operation of up to the number of bytes returned from available() will not block; however, there is no guarantee that attempts to read or write more data will block.

Return
the amount of data available, in bytes
Drains queued data from the line by continuing data I/O until the data line's internal buffer has been emptied. This method blocks until the draining is complete. Because this is a blocking method, it should be used with care. If drain() is invoked on a stopped line that has data in its queue, the method will block until the line is running and the data queue becomes empty. If drain() is invoked by one thread, and another continues to fill the data queue, the operation will not complete. This method always returns when the data line is closed.
See Also
Flushes queued data from the line. The flushed data is discarded. In some cases, not all queued data can be discarded. For example, a mixer can flush data from the buffer for a specific input line, but any unplayed data already in the output buffer (the result of the mix) will still be played. You can invoke this method after pausing a line (the normal case) if you want to skip the "stale" data when you restart playback or capture. (It is legal to flush a line that is not stopped, but doing so on an active line is likely to cause a discontinuity in the data, resulting in a perceptible click.)
See Also
Obtains the maximum number of bytes of data that will fit in the data line's internal buffer. For a source data line, this is the size of the buffer to which data can be written. For a target data line, it is the size of the buffer from which data can be read. Note that the units used are bytes, but will always correspond to an integral number of sample frames of audio data.
Return
the size of the buffer in bytes
Obtains the current format (encoding, sample rate, number of channels, etc.) of the data line's audio data.

If the line is not open and has never been opened, it returns the default format. The default format is an implementation specific audio format, or, if the DataLine.Info object, which was used to retrieve this DataLine, specifies at least one fully qualified audio format, the last one will be used as the default format. Opening the line with a specific audio format (e.g. ) will override the default format.

Return
current audio data format
See Also
Obtains the current position in the audio data, in sample frames. The frame position measures the number of sample frames captured by, or rendered from, the line since it was opened. This return value will wrap around after 2^31 frames. It is recommended to use getLongFramePosition instead.
Return
the number of frames already processed since the line was opened
Obtains the current volume level for the line. This level is a measure of the signal's current amplitude, and should not be confused with the current setting of a gain control. The range is from 0.0 (silence) to 1.0 (maximum possible amplitude for the sound waveform). The units measure linear amplitude, not decibels.
Return
the current amplitude of the signal in this line, or {@link AudioSystem#NOT_SPECIFIED}
Obtains the current position in the audio data, in sample frames. The frame position measures the number of sample frames captured by, or rendered from, the line since it was opened.
Return
the number of frames already processed since the line was opened
@since
1.5
Obtains the current position in the audio data, in microseconds. The microsecond position measures the time corresponding to the number of sample frames captured by, or rendered from, the line since it was opened. The level of precision is not guaranteed. For example, an implementation might calculate the microsecond position from the current frame position and the audio sample frame rate. The precision in microseconds would then be limited to the number of microseconds per sample frame.
Return
the number of microseconds of data processed since the line was opened
Indicates whether the line is engaging in active I/O (such as playback or capture). When an inactive line becomes active, it sends a START event to its listeners. Similarly, when an active line becomes inactive, it sends a STOP event.
Return
true if the line is actively capturing or rendering sound, otherwise false
Indicates whether the line is running. The default is false. An open line begins running when the first data is presented in response to an invocation of the start method, and continues until presentation ceases in response to a call to stop or because playback completes.
Return
true if the line is running, otherwise false
See Also
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
formatthe desired audio format
Throws
LineUnavailableExceptionif the line cannot be opened due to resource restrictions
IllegalArgumentExceptionif format is not fully specified or invalid
IllegalStateExceptionif the line is already open
SecurityExceptionif the line cannot be opened due to security restrictions
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
formatthe desired audio format
bufferSizethe desired buffer size, in bytes.
Throws
LineUnavailableExceptionif the line cannot be opened due to resource restrictions
IllegalArgumentExceptionif the buffer size does not represent an integral number of sample frames, or if format is not fully specified or invalid
IllegalStateExceptionif the line is already open
SecurityExceptionif the line cannot be opened due to security restrictions
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
ba byte array that will contain the requested input data when this method returns
offthe offset from the beginning of the array, in bytes
lenthe requested number of bytes to read
Return
the number of bytes actually read
Throws
IllegalArgumentExceptionif the requested number of bytes does not represent an integral number of sample frames. or if len is negative.
ArrayIndexOutOfBoundsExceptionif off is negative, or off+len is greater than the length of the array b.
Allows a line to engage in data I/O. If invoked on a line that is already running, this method does nothing. Unless the data in the buffer has been flushed, the line resumes I/O starting with the first frame that was unprocessed at the time the line was stopped. When audio capture or playback starts, a START event is generated.
Stops the line. A stopped line should cease I/O activity. If the line is open and running, however, it should retain the resources required to resume activity. A stopped line should retain any audio data in its buffer instead of discarding it, so that upon resumption the I/O can continue where it left off, if possible. (This doesn't guarantee that there will never be discontinuities beyond the current buffer, of course; if the stopped condition continues for too long, input or output samples might be dropped.) If desired, the retained data can be discarded by invoking the flush method. When audio capture or playback stops, a STOP event is generated.