How to fix wait and notify

Question

The program tries to find the first socket connection. Theirs a wait and the notify call in the inner class seams to have to effect. Attach is the code to try out
import java.io.*;
import java.util.*;
import java.net.*;
import java.nio.channels.*;
* SocketSearch class to scan for an open socket from an array of sockets passed. <br>
* Inner class DetectSocketConnection tries to open the socket and assign hostname
* a value if successful. <br>
* The SocketSearch thread class is waiting to find the hostname or active DetectSocketConnection
* threads to be zero - i.e No hosts found
public class SocketSearch extends Thread {
   private Object syncObject = new Object();
   private String hostname = null;
   private ThreadGroup threadGroup = new ThreadGroup("SOCKETS_CONNECT");
   private ArrayList sockets = null;
    * Inner class DetectSocketConnection to find an open socket. <br>
    * It will assign the hostname a value if successful
   private class DetectSocketConnection extends Thread {
      private SocketChannel sc = null;
      private String host = null;
      private int port = -1;
      public DetectSocketConnection(String host, int port) {
         super(threadGroup, host);
         this.host = host;
         this.port = port;
         System.out.println("DetectSocketConnection::syncObject = " + syncObject);     
      public void run() {
         System.out.println("Scanning " + host + " at port number " + port);
         synchronized(syncObject) {
            try {         
               InetSocketAddress isa = new InetSocketAddress(InetAddress.getByName(host), port);
                   // Connect
                sc = SocketChannel.open();
            sc.connect(isa);
               System.out.println("Found hostname: " + host + "!!!!!!!!!!!!!!!!!!!");
               hostname = host;
            catch (IOException e) {
               System.err.println("DetectSocketConnection: " + e.toString());
            finally {
            // Make sure we close the channel (and hence the socket)
               close();
               System.out.println("DetectSocketSonnectio: notify()...");
               syncObject.notify();
      public void close() {
         try {
            if (sc != null) sc.close();
         catch (IOException e) {
   public SocketSearch() {
      sockets = new ArrayList();
    * Add socket to the sockets ArrayList to prepare to start the Socket Search
    * @param host Socket hostname
    * @param port Socket port number
   public void addSocket(String host, int port) {
      DetectSocketConnection detectSocket = new DetectSocketConnection(host, port);
      sockets.add(detectSocket);
    * SocketSearch start method to fire up the sockets threads to search for
   public void start() {
      super.start();
      if (sockets != null) {
         DetectSocketConnection[] arrSockets = (DetectSocketConnection[]) sockets.toArray(new DetectSocketConnection[0]);
         for (int i = 0 ; i < arrSockets.length ; i++) {
            arrSockets.start();
* Main code to do the socket search
public void run() {
try {
boolean loop = (sockets.size() > 0);
while (loop) {
synchronized(syncObject) { 
System.out.println("SocketSearch.wait() => syncObject = " + syncObject);
syncObject.wait();
System.out.println("SocketSearch.wait() => syncObject = " + syncObject + ", finished...");
if (hostname != null) {     
// use the hostname
// you could interrupt the threads now - its your choice
loop = false;
else {
System.out.println("Invalid hostname...");
ThreadGroup currentGroup = Thread.currentThread().getThreadGroup();
int numThreads = currentGroup.activeCount();
Thread[] listOfThreads = new Thread[numThreads];
currentGroup.enumerate(listOfThreads);
int activeThreads = 0;
for (int i = 0 ; i < numThreads ; i++) {
if (listOfThreads[i] instanceof DetectSocketConnection) {
activeThreads++;
System.out.println("activeThreads: " + activeThreads);
if (activeThreads == 0) {     
// host name is NULL and active threads are finished
throw new UnknownHostException("Host not found.");
if (hostname != null) {
System.out.println("Found hostname: " + hostname);
// Do something here, use callback to maybe dispose ProgressDialog etc...
catch (UnknownHostException e) {
// Do something here, use callback to maybe dispose ProgressDialog etc...
System.err.println(e.toString());
catch (InterruptedException e) {
// Do something here, use callback to maybe dispose ProgressDialog etc...
System.err.println(e.toString());
* Test to find a socket from an array of test socket hosts
public static void main(String args[]) {
String[] yahooPOP3PossibleSettings = new String[] {
"yahoo.com",
"mail.yahoo.com",
"pop.yahoo.com",
"pop.mail.yahoo.com",
"pop3.yahoo.com"
int PORT_NUMBER = 110;
SocketSearch socketSearch = new SocketSearch();
for (int i = 0 ; i < yahooPOP3PossibleSettings.length ; i++) {
socketSearch.addSocket(yahooPOP3PossibleSettings[i], PORT_NUMBER);
socketSearch.start();

Answer 1

Forget it. The Inner class was doing a wait and so was the main thread.
Not meant to put a wait in the main thread...