Java ByteBuffer

from java.sun.com
Invariants

The following invariant holds for the mark, position, limit, and capacity values:

0 <= mark <= position <= limit <= capacity

A newly-created buffer always has a position of zero and a mark that is undefined. The initial limit may be zero, or it may be some other value that depends upon the type of the buffer and the manner in which it is constructed. The initial content of a buffer is, in general, undefined.
Clearing, flipping, and rewinding

In addition to methods for accessing the position, limit, and capacity values and for marking and resetting, this class also defines the following operations upon buffers:

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clear() makes a buffer ready for a new sequence of channel-read or relative put operations: It sets the limit to the capacity and the position to zero.
*

flip() makes a buffer ready for a new sequence of channel-write or relative get operations: It sets the limit to the current position and then sets the position to zero.
*

rewind() makes a buffer ready for re-reading the data that it already contains: It leaves the limit unchanged and sets the position to zero.