Java Selector behaviour

output

Selecting r, return 1: r
recv 21 bytes
Selecting r, return 0: r
recv 0 bytes
Selecting rw, return 1: w
Selecting r, return 0: w

TestSelect.java

import java.net.InetSocketAddress;
import java.nio.channels.Selector;
import java.nio.channels.SelectionKey;
import java.nio.channels.SocketChannel;
import java.nio.ByteBuffer;

public class TestSelect
{
	public static void main (String [] args) throws Exception
	{
		SocketChannel socket = SocketChannel.open(new InetSocketAddress("127.0.0.1", 22));
		socket.configureBlocking(false);
		Selector selector = Selector.open();
		SelectionKey selkey = socket.register(selector, 0);
		int selected;

		for (int i = 0; i < 2; i ++) {
			selkey.interestOps(SelectionKey.OP_READ);
			selected = selector.select(1000);
			System.out.println("Selecting r, return " + selected + ": " +
					(selector.selectedKeys().contains(selkey) && selkey.isReadable() ? "r" : "") +
					(selector.selectedKeys().contains(selkey) && selkey.isWritable() ? "w" : ""));
			ByteBuffer buffer = ByteBuffer.allocate(100);
			int size = socket.read(buffer);
			System.out.println("recv " + size + " bytes");
		}

		selkey.interestOps(SelectionKey.OP_READ | SelectionKey.OP_WRITE);
		selected = selector.select(1000);
		System.out.println("Selecting rw, return " + selected + ": " +
				(selector.selectedKeys().contains(selkey) && selkey.isReadable() ? "r" : "") +
				(selector.selectedKeys().contains(selkey) && selkey.isWritable() ? "w" : ""));

		selkey.interestOps(SelectionKey.OP_READ);
		selected = selector.select(1000);
		System.out.println("Selecting r, return " + selected + ": " +
				(selector.selectedKeys().contains(selkey) && selkey.isReadable() ? "r" : "") +
				(selector.selectedKeys().contains(selkey) && selkey.isWritable() ? "w" : ""));
	}
}