Ambiguous call to constructor “super(null)” in java.net.DatagramSocket?

Question

I am extending the class Java.net.DatagramSocket and giving the subclass its own constructor. The constructor for my new class, UDP_Socket , is as follows

private UDP_Socket(int port) throws IOException {
    super(null); // Creates an unbound socket.
    super.setReuseAddress(true); // You set reuse before binding.
    super.bind(new InetSocketAddress(port)); // finally, bind
}

The only problem is on the line super(null) , I am getting ambiguous reference to both constructor DatagramSocket(DatagramSocketImpl) and DatagramSocket(SocketAddress) . I need the super(null) line to create an unbound socket and I believe that I am supposed to set the reuse address socket option before binding. How do I fix this error?

Answer 1

The problem is because you call super(null) is valid parameter to both DatagramSocket(DatagramSocketImpl) and DatagramSocket(SocketAddress) .

So, the compiler is confused. You can call only one of the constructors.

Use,

super((DatagramSocketImpl) null);

or,

super((SocketAddress) null);

depending on which constructor you want to call.

Answer 2

The error:

ambiguous reference to both constructor DatagramSocket(DatagramSocketImpl) and DatagramSocket(SocketAddress)

Is telling you that null can reference (DatagramSocketImpl) null or (SocketAddress) null thus making it ambiguous.

You must explicitly call one of the two constructors

 // super((DatagramSocketImpl) null)
 super((SocketAddress) null)

or have your constructor require that

private UDP_Socket(int port, SocketAddress addr) throws IOException {
    super(addr);

Edit:

Code from: Class DatagramSocket

 private DatagramSocket getDatagramSocket (int port) {
    DatagramSocket s = new DatagramSocket(null);
    s.setReuseAddress(true);
    s.bind(new InetSocketAddress(port));

    return s;
 }