Oracle database 12c Error while trying to connect: The Network Adapter could not establish the connection

Question

I installed Oracle database 12c for the first time. I followed correctly all the steps and installed it on Windows 7 64 bits, but when I click on SQL Developer and try to create a new connection, I put in the informations like Username and password, and finnaly click on TEST button, I get this error message: "The Network Adapter could not establish the connection".

I dont know what to do anymore, I read tutorials and cant solve that error. Also, when I open SQL Developer, i get a message saying Im using a java version that is not supported by Oracle Database, Im using java 1.8 and it says I should use from 1.6 to 1.7 only. im not sure if that is causing something bad but it seems fine because I can go further using the SQL Dev. So, what should i do? Thank you very much!

Solution

Here are some things to check:

1. Ensure that the TNSNAMES.ORA file is properly configured to reference the database. Check for the SID, host name, and port number (typically 1521).

2. Check whether you can connect directly from the server, such as with SQL PLus. This should isolate whether it's a server or client problem.

3. Ensure that the Listener service on the server is running. Check that LISTENER.ORA is properly configured.

4. I encountered a situation in the past where client PCs could not connect. I found that by deleting (or renaming) the SQLNET.ORA file, the connection could be made.

Good luck.