Threading in Java: How to lock an object?

Question

The following Function is executing in its own thread:

private void doSendData() {     try {             //writeToFile(); // just a temporary location of a call            InetAddress serverAddr = InetAddress.getByName(serverAddress);            serverAddr.wait(60000);            //Log.d("TCP", "C: Connecting...");            Socket socket = new Socket(serverAddr, portNumber);            socket.setSoTimeout(3000);                 try {                 //Log.d("TCP", "C: Sending: '" + message + "'");                 PrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter(socket.getOutputStream())),true);                 String message = packData();                 out.println(message);                 Log.d("TCP", "C: Sent.");                 Log.d("TCP", "C: Done.");                 connectionAvailable = true;               } catch(Exception e) {                  Log.e("TCP", "S: Error", e);                  connectionAvailable = false;                 } finally {                   socket.close();                   announceNetworkAvailability(connectionAvailable);                 }           } catch (Exception e) {               Log.e("TCP", "C: Error", e);               announceNetworkAvailability(connectionAvailable);          } } 

When the execution reaches the line serverAddr.wait(60000) it throws an Exception:

java.lang.IllegalMonitorStateException: object not locked by thread before wait() 

Does anyone know how to lock an object or a function in order to prevent the concurrency? I've tried to add a Lock object:

private final Lock lock = new ReentrantLock(); 

and the line

boolean locked = lock.tryLock(); 

at the beginning of function but it didn't work.

Answer 1

In order to call wait() on an object, you have to hold the synchronized lock on that object (though the lock is actually released while the thread is waiting):

synchronized (serverAddr) {   serverAddr.wait(); } 

I have to admit that why you're wanting to do this baffles me in this case...