Question

I’m trying to develop a program that takes requests for data which is stored in a map. The map is declared in the main method as shown below:

Map m = Collections.synchronizedMap(new HashMap());
synchronized(m) {
        while (listening) {

            new BrokerLookupServerHandlerThread(serverSocket.accept(), m).start();

        }
}

The code for the BrokerLookupServerHandlerThread takes the input and makes it one of the object’s variables. If I use it in this class, will the original map be updated as well? I understand that Java is pass by value, (I’m used to C/C++) so I just wanted to be sure if this implementation of a synchronized object makes sense.

    private Socket socket = null;
//private String t ="MSFT";
public Map m;

public BrokerLookupServerHandlerThread(Socket socket, Map m) {
    super("NamingServerHandlerThread");
    this.socket = socket;
    this.m = m;
    System.out.println("Created new Thread to handle client");
}

Thanks for your help.

Answer 1

Yes original object will be updated. I suggest you use ConcurrentHashMap though.

A hash table supporting full
concurrency of retrievals and
adjustable expected concurrency for
updates. This class obeys the same
functional specification as Hashtable,
and includes versions of methods
corresponding to each method of
Hashtable. However, even though all
operations are thread-safe,
retrieval operations do not entail locking, and there is not any
support for locking the entire table
in a way that prevents all access.
This class is fully interoperable with
Hashtable in programs that rely on its
thread safety but not on its
synchronization details.