A line can have controls, such as gain, pan, and reverb. The controls themselves are instances of classes that extend the base Control class. The Line interface provides two accessor methods for obtaining the line's controls: getControls returns the entire set, and getControl returns a single control of specified type.

Lines exist in various states at different times. When a line opens, it reserves system resources for itself, and when it closes, these resources are freed for other objects or applications. The isOpen() method lets you discover whether a line is open or closed. An open line need not be processing data, however. Such processing is typically initiated by subinterface methods such as SourceDataLine.write and TargetDataLine.read.

You can register an object to receive notifications whenever the line's state changes. The object must implement the LineListener interface, which consists of the single method update. This method will be invoked when a line opens and closes (and, if it's a DataLine , when it starts and stops).

An object can be registered to listen to multiple lines. The event it receives in its update method will specify which line created the event, what type of event it was (OPEN, CLOSE, START, or STOP), and how many sample frames the line had processed at the time the event occurred.

Certain line operations, such as open and close, can generate security exceptions if invoked by unprivileged code when the line is a shared audio resource.