Connecting to unavailable hosts is possible in java with OP_CONNECT, connect, and finishConnect

ConnectionTest.java

package example;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;

public class ConnectionTest {
    public static final InetSocketAddress unavailableHostAddress = new InetSocketAddress("10.10.10.10", 6666);

    public static void main(String[] args) throws IOException {
        SocketChannel ch = SocketChannel.open();
        ch.configureBlocking(false);

        Selector sel = Selector.open();
        SelectionKey key = ch.register(sel, SelectionKey.OP_CONNECT);

        int selected = sel.select();
        assert(selected == 1); // wtf 1
        assert(key.isConnectable() == true); // wtf 2
        System.out.println("Is connectable: "+key.isConnectable());

        boolean directlyConnected = ch.connect(unavailableHostAddress);
        assert(directlyConnected == false);
        assert(ch.isConnected() == false);
        assert(ch.isConnectionPending() == true);
        System.out.println("Directly connected: "+directlyConnected+" ch.isConnected: "+ch.isConnected()+" ch.isConnectionPending: "+ch.isConnectionPending());

        // we know, this should succeed because of `key.isConnectable()`
        boolean finishedConnecting = ch.finishConnect();
        assert(finishedConnecting == true); // wtf 3 !!!
        assert(ch.isConnected() == true); // wtf 4
        System.out.println("finishConnect() returned: "+finishedConnecting+" ch.isConnected: "+ch.isConnected());
    }
}