I believe HimanshuTayal gave you the cirrect info to register the driver;
DriverManager.registerDriver( new oracle.jdbc.driver.OracleDriver());
However, you may also want to check your environment to be sure you are using the correct Oracle driver. You can get the applicable Oracle packagehere, https://www.soapui.org/jdbc/reference/jdbc-drivers.html. Saved the driver package in the "C:\Program Files\SmartBear\ReadyAPI-3.0.0\bin\ext" directory for the connection to be established. As a side note, when you upgrade to another version of Ready API you will need to move the oracle file to the new release directory.
Hope this helps you get the problem resolved.
I checked correct ojdbc driver present in EXT folder. However earlier i was able to connect to database but when i reset the password the issue occured to me. i tried uninstalling ready api and installed again but didnt worked.
@PratikshaMehete : Is your issue resolved or still you are searching for the solution, if it is resolved please let us all know that how you managed to solved the issue so that it will be helpful for anyother help seeker.