Java SE NIO

NIO basic concepts Demonstrate the understanding of basic NIO ideology

• Explain the differences in approaches between NIO and classical IO
• Enumerate the main usages of NIO (like non-blocking IO)

Buffers Show ability to manipulate ByteBuffer (specific functions for HeapByteBuffer, DirectByteBuffer and MappedByteBuffer are not covered)

• Be able to write code that uses buffers:
  • Create ByteBuffer
  • Add data to buffer
  • Remove data from buffer
• Be able to use each buffer's parameter:
  • position
  • limit
  • capacity
• Explain why 0 <= mark <= position <= limit <= capacity is true in all cases

Channels Display understanding of channels

• Explain the purpose of using channels
• Describe the purpose of basic channel interfaces and classes:
  • Channel
  • ReadableByteChannel
  • WritableByteChannel
  • ByteChannel
  • FileChannel
  • SocketChannel
  • DatagramChannel
• Write code to construct and use FileChannel and SocketChannel:
  • Create channels:
    • RandomAccessFile.getChannel()
    • Socket.getChannel()
  • Write data to channel:
    • WritableByteChannel.write(ByteBuffer src);
    • Note that write operation might not write all the buffer during one writing loop.
  • Read data from channel:
    • ReadableByteChannel.read(ByteBuffer dst);
    • Note that read operation might not fill all the buffer during one reading loop.
  • Close channel
  • Handle channels' exceptions

Selectors This category covers questions about selectors - an approach to handle large number of reading/writing channels simultaneously.

• Give usage description for basic classes:
  • Selector
    • Opening selector
    • Selecting keys:
      • Use Selector.select() to get ready selection keys
      • Explain difference between Selector.select() and Selector.select(int)
    • Be able to stop key selection process using wakeUp()
    • Closing selector
  • SelectableChannel
    • Bind channel to Selector in different modes:
      • SelectionKey.OP_ACCEPT
      • SelectionKey.OP_CONNECT
      • SelectionKey.OP_READ
      • SelectionKey.OP_WRITE
      • Be able to use the appropriate mode in a given situation
  • SelectionKey
    • Explain what SelectionKey is used for
    • Use SelectionKey.attach(Object) and SelectionKey.attachment() to manipulate SelectionKey's specific data
  • Be able to write code that uses them
• Explain the difference SelectableChannel's blocking and non-blocking modes.
  Be able to choose the most appropriate mode in a given situation.
• Explain why selectors can be scaled (no need to use a thread per connection)