Whats the difference between a socket which is open and a socket which is connected?

Question

The Java Socket class has two methods isClosed and isConnected to check whether the socket is closed or connected respectively. I want

Answer 1

To put things simply, a Socket that is open is a socket that is either waiting for connection or has successfully connected with another Socket. When a socket has been closed, it means that this socket is no longer available for connection, and that it's resources has already been released. A Socket that is connected, well, it means that the socket is connected to another Socket.

So a Socket can..

• be open and connected at the same time.
• be open and not connected at the same time.
• not be connected when closed.

UPDATE

from @Bryan

Apparently, there are half-closed or half-open states for TCP Sockets; which usage (today) is different from its original meaning. More on this link.