Oracle SQL Developer: Failure - Test failed: The Network Adapter could not establish the connection?

I am answering this for the benefit of future community users. There were multiple issues. If you encounter this problem, I suggest you look for the following:

• Make sure your tnsnames.ora is complete and has the databases you wish to connect to
• Make sure you can tnsping the server you wish to connect to
• On the server, make sure it will be open on the port you desire with the specific application you are using.

Once I did these three things, I solved my problem.

I had a similar issue where I also continuously got the same error. I tried many things like changing the listener port number, turning off the firewall etc. Finally I was able to resolve the issue by changing listener.ora file. I changed the following line:

(ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))

to

(ADDRESS = (PROTOCOL = TCP)(HOST = hostname)(PORT = 1521)) 

I also added an entry in the /etc/hosts file.

you can use Oracle net manager to change the above line in listener.ora file. See Oracle Net Services Administrator's Guide for more information on how to do it using net manager.

Also you can use the service name (database_name.domain_name) instead of SID while making the connnection.

I Hope it helps.

I just had same issue when I installed the oracle 11g and then creating the database.

I don't even know that the listener has to create manually. Hence, I open Net Configuration Assistant and manually create the listener.

And I can connect the database that I created locally through sql developer.