When a ServerSocket object is created, it attempts to bind to the port on the local host given by the port argument.
When a ServerSocket object is created, it attempts to bind to the port on the local host given by the port argument.
If another server socket is already listening to the port, then a java.net.BindException, a subclass of IOException, is thrown.
No more than one process or thread can listen to a particular port at a time. This includes non-Java processes or threads.
For example, if there's already an HTTP server running on port 80, you won't be able to bind to port 80.