FileOutputStream is for writing to a file;
BufferOutputStream writes to a buffer;
You can create one and pass it to any of the table writers, for example.
The $create() factory methods instantiate the OutputStream object and
take the following arguments, depending on the subclass:
path For FileOutputStream, a character file name
initial_capacity For BufferOutputStream, the size in bytes of the
buffer.
$tell(): return the position in the stream
$close(): close the stream
$write(x): send x to the stream
$capacity(): for BufferOutputStream
$finish(): for BufferOutputStream
$GetExtentBytesWritten(): for MockOutputStream, report how many bytes
were sent.