Nonblocking I/O - Java Network Programming - page 361

mark
A client-specified index in the buffer. It is set at the current position by invoking
the mark() method. The current position is set to the marked position by invoking
reset() :
public final Buffer mark ()
public final Buffer reset ()
If the position is set below an existing mark, the mark is discarded.
Unlike reading from an InputStream , reading from a buffer does not actually change
the buffer's data in any way. It's possible to set the position either forward or backward
so you can start reading from a particular place in the buffer. Similarly, a program can
adjust the limit to control the end of the data that will be read. Only the capacity is fixed.
The common Buffer superclass also provides a few other methods that operate by
reference to these common properties.
The clear() method “empties” the buffer by setting the position to zero and the limit
to the capacity. This allows the buffer to be completely refilled:
public final Buffer clear ()
However, the clear() method does not remove the old data from the buffer. It's still
present and could be read using absolute get methods or changing the limit and position
again.
The rewind() method sets the position to zero, but does not change the limit:
public final Buffer rewind ()
This allows the buffer to be reread.
The flip() method sets the limit to the current position and the position to zero:
public final Buffer flip ()
It is called when you want to drain a buffer you've just filled.
Finally, there are two methods that return information about the buffer but don't change
it. The remaining() method returns the number of elements in the buffer between the
current position and the limit. The hasRemaining() method returns true if the number
of remaining elements is greater than zero:
public final int remaining ()
public final boolean hasRemaining ()
Creating Buffers
The buffer class hierarchy is based on inheritance but not really on polymorphism, at
least not at the top level. You normally need to know whether you're dealing with an