Buffer<type> {
   a linear sequence of <type>s.

   int position, limit, capacity;

   invariants:
     - capacity never changes (after initialization);
     - 0 <= position <= limit <= capacity;
     - remaining() == limit - position
     - at any time, the buffer contains limit <type>s

     - Buffer<byte>s (java.nio.ByteBuffer) may be /direct/, meaning
       that they represent data buffers in native code (outside the
       JVM's heap). Useful for high-performance data sharing with
       non-Java code (cf. JOGL, or memory-mapped files (see
       FileChannel below), which effectively maps the OS's buffer
       cache into the JVM directly)

       - non-byte Buffers may be created as "view buffers" into a byte
         buffer, combining (without copying) the bytes into the view
         buffer's element types using a specified byte
         ordering/endianness etc.

   operations:

     - transferring <type>s to/from the buffer from/to <type>[]s or
       other buffer<type>s.

       (relative) transfers from the buffer read their <type>s
       starting at position, advancing position acordingly if the read
       succeeded, or throwing BufferUnderflowException (and not
       changing the buffer's state in any way) if more than
       remaining() <type>s would have had to be read.

       (relative) transfers to the buffer write their <type>s starting
       at position, advancing position acordingly if the write
       succeeded, or throwing BufferOverflowException (and not
       changing the buffer's state in any way) if more than
       remaining() <type>s would have had to be written.

};


Channel {

    represents a connection to some data source or -sink (e.g. a
    Buffer<byte> or another channel). May be open or closed at a given
    time. Once closed, it remains closed.

    Some channels (e.g. FileChannel; see below) may have a current
    position inside their stream.

    Subclasses/subinterfaces provide specific functionality,
    e.g. readability, writability (or both), blockable/non-blockable
    etc.:

    - ReadableByteChannel: interface for channels which bytes can be
      read from (into a ByteBuffer)

      - ScatteringByteChannel extends ReadableByteChannel: interface
        for ReadableByteChannels that "scatter" their output into
        multiple buffers (potentially more efficient than using byte[]
        arrays and performing the scattering manually)

    - WritableByteChannel: interface for channels which bytes can be
      written to (from a ByteBuffer)

      - GatheringByteChannel extends WritableByteChannel: interface
        for WritableByteChannels that "gather" their input from
        multiple buffers (potentially more efficient than using byte[]
        arrays and performing the gathering manually)

    - ByteChannel implements ReadableByteChannel, WritableByteChannel


    - InterruptibleChannel: interface for channels that are
      "asynchronously closeable": one thread may close the channel
      while another one blocks in an I/O operation; the latter thread
      will receive a AsynchronousCloseException.

    - SelectableChannel implements InterruptibleChannel

      Channel that may be set to "non-blocking" mode and then be
      registered with a "Selector". Several SelectableChannels can be
      registered with the same selector, which can then be queried for
      whether specific I/O events have occured on some of the
      registered channels.

      Key methods:

      - configureBlocking(boolean block)

        set to blocking/non-blocking mode

      - SelectionKey register(Selector sel, int ops)

        register this channel with Selector sel, waiting for I/O
        events of the types specified in ops (one or more of
        SelectionKey.OP_ACCEPT, SelectionKey.OP_CONNECT,
        SelectionKey.OP_READ, SelectionKey.OP_WRITE). The returned
        "SelectionKey" represents the registration (later querying
        whether an event has occured on this SelectionKey:
        sel.selectedKeys().contains(theSelectionKey))


    - FileChannel implements InterruptibleChannel, ByteChannel,
      GatheringByteChannel, ScatteringByteChannel

      Channel that wraps an open file.

      Has a current position inside the file stream that may be
      queried and modified.

      A region of the file may be mapped  directly into memory.

      A region of the file may be locked against access by other
      programs

      transferTo(long position, long count, WritableByteChannel
                 target):

      - transfer data from this FileCHannel to another channel. VM
        vendor may have provided an efficient native implementation
        (e.g. ("zero copy" etc.) that is much faster than copying
        manually via byte[] buffers


      transferFrom(ReadableByteChannel src, long position, long count)

      - same thing for the opposite direction

    - SocketChannel implements SelectableChannel, ByteChannel,
      ScatteringByteChannel, GatheringByteChannel

      A selectable channel for stream-oriented sockets.


}