In JCo3.0, Java client JCO.Client is replaced by JCoDestinations. You can connect to SAP system via Inbound RFC Communication (Java calls ABAP) or via Outbound RFC Communication (ABAP calls Java).
For inbound RFC communication, you need to use JCoDestination for executing a remote function module at ABAP side. To use inbound RFCs, you have to use “JCoDestination” which executes a Function module remotely at ABAP side and while using outbound RFCs, you have to configure a JCoServer at the SAP gateway that is responsible to receive incoming requests from ABAP side and process remote function module at Java side.
To know more about configuring JCo connection for inbound and outbound processing, you can refer below link: