1)EventExecutorGroup: The EventExecutorGroup is responsible for providing the EventExecutor's to use via its next() method.
2)AbstractEventExecutorGroup: Abstract base class for EventExecutorGroup implementations.
3)MultithreadEventExecutorGroup: Abstract base class for EventExecutorGroup implementations that handles their tasks with multiple threads at the same time.
4)MultithreadEventLoopGroup: Abstract base class for EventLoopGroup implementations that handles their tasks with multiple threads at the same time.
5)NioEventLoopGroup: MultithreadEventLoopGroup implementations which is used for NIO Selector based Channels.