SelectableChannel.register() allows to register with Selector for Operations which do not have any meaning.
For Example ServerSocketChannel can be registered with Selector for the operation 0,
allowing selector.select() to wait forever.
Similarly , SocketChannel can be registered for the operation 0,5,9,12,13 with selector,
DatagramChannel for 0, 5, and Pipe.SinkChannel/SourceChannel can be register with selector
for operation 0.

Clearly registering Channels for operations other than SelectionKey.OP_READ/OP_WRITE/OP_CONNECT/OP_ACCEPT
is not useful. it is should throw IllegalArgumentException.

Please see the following code and Result,
OS : Windows2000Prof.
<jdk-version>
client24 /home/rg157576 $ java -version
java version "1.6.0-rc"
Java(TM) SE Runtime Environment (build 1.6.0-rc-b89)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b89, mixed mode)
</jdk-version>

<code>
import java.nio.*;
import java.nio.channels.*;

public class UnknownOps {
  public static void main(String... args ) throws Exception {
SelectableChannel ch[] = {SocketChannel.open(),ServerSocketChannel.open(),DatagramChannel.open()};
Selector selector = Selector.open();
for (SelectableChannel channel : ch) {
channel.configureBlocking(false);
for (int j=0;j<15;j++) {
try {
channel.register(selector,j);
if (!(j== 1 || j==4 || j==8 || j==16)) {
System.out.println("Channel "+channel.getClass().getName()+" Register for Unvalid Ops "+j);
}
}catch(Exception e) {
//System.out.println("j"+j);
//e.printStackTrace();
}
}
}
  }
}
</code>
<Result>

Channel sun.nio.ch.SocketChannelImpl Register for Unvalid Ops 0
Channel sun.nio.ch.SocketChannelImpl Register for Unvalid Ops 5
Channel sun.nio.ch.SocketChannelImpl Register for Unvalid Ops 9
Channel sun.nio.ch.SocketChannelImpl Register for Unvalid Ops 12
Channel sun.nio.ch.SocketChannelImpl Register for Unvalid Ops 13
Channel sun.nio.ch.ServerSocketChannelImpl Register for Unvalid Ops 0
Channel sun.nio.ch.DatagramChannelImpl Register for Unvalid Ops 0
Channel sun.nio.ch.DatagramChannelImpl Register for Unvalid Ops 5

</Result>