Discards the initial portion of the stream prior to the indicated position. Attempting to seek to an offset within the flushed portion of the stream will result in an
IndexOutOfBoundsException.
Calling flushBefore may allow classes implementing this interface to free up resources such as memory or disk space that are being used to store data from the stream.
@param pos a long containing the length of thestream prefix that may be flushed.
@exception IndexOutOfBoundsException if pos liesin the flushed portion of the stream or past the current stream position.
@exception IOException if an I/O error occurs.