Why FileChannel in Java is not non-blocking?

Simply put, most operating systems doesn't treat regular files as something that can block - so they don't allow you explicitly set them to a non-blocking state.

UNIX does not support non-blocking I/O for files, see Non-blocking I/O with regular files. As Java should (at least try to) provide the same behaviour on all platforms, the FileChannel does not implement SelectableChannel.

However Java 7 will include a new AsynchronousFileChannel class that supports asynchronous file I/O, which is a different mechanism to non-blocking I/O.

In general only sockets and pipes truly support non-blocking I/O via select() mechanism.