Question

Picture that you have a chat program where you want to send and recive data to & from the server. would it be smart to turn the clients connection into a singleton? or will this ruin the data stream.

my example of a client singleton:

public class Client {
    private static Client client;
    private final int portNumber = 7070;
    private Socket socket;
    private Client(){
        connect();

    }
    public static synchronized Client getClient(){
        if (client == null) {
            client = new Client();
        }
        return client;
    }

    public void connect(){

        try {
            InetAddress adr = InetAddress.getByName("localhost");
            socket = new Socket(adr, portNumber);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

Answer 1

There are two issues with your code:

• singletons are very inflexible. If you want to implement load-balancing or connection pooling in the future, your hands are tied. Only one connection is allowed. And what about reconnecting? How do you get rid of old connection and create a new one?

• connecting (or any operation that has side-effects) inside a constructor is not a good practice. Imagine unit-testing this class

So I don’t advice singleton connection object. Instead have a ClientConnections manager class with Client connect() method. This manager class keeps track of all opened connections, can cache them, close unused, test periodically, etc. ClientConnections is a better candidate for singleton.