calling new thread inside is constructor

Question

Is it correct to create a thread and call its start() method inside a class' constructor as done here?

public class Server implements Runnable {

    private ServerSocket server;

    public Server(int port) {
        try {
            //Opens a new server 
            server = new ServerSocket(port);
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }

        new Thread(this, "Server").start();
    }

    @Override
    public void run() {
    }
}

Answer 1

IMHO, do not do this. You're allowing the this reference to escape during construction.

Answer 2

Granted, your code isnt doing it but what if your code looked like this:

public Server(int port)
{       
    new Thread(this, "Server").start();

    try
    {
        //Opens a new server 
        server = new ServerSocket(port);
    }
    catch (IOException ioe){ ioe.printStackTrace(); }

}
@Override    
public void run(){
    if(server == null)throw new NullPointerException();// this may happen
}
}

The server reference may be null even though no exception occurs. This is because the Thread will use the created runnable and invoke the run method even if the constructor of your class hasn't finished.