Android java class/symbol not found despite being placed in the same directory

I have encountered issues in my android studio regarding java classes/symbols not found, despite these classes and symbols being placed in the same directory, or under the same parent directory. I am making use of the DJI's mobile SDK for android.

Example of errors:

Cannot resolve symbol 'DJISampleApplication'

For illustration, here are 2 screenshots First example. Clicking on "import class" causes android studio to create a brand new class instead of linking it to the existing one.

second example

However, oddly, when I go under "Build >> Make Project" , or "Run" to deploy on a real android device, the app can be installed, and there are no errors (only warnings).

Things I have tried:

1. Uninstalling and re-installing android studio
2. copying the whole project from the original files in again
3. Trying on another computer, which works. However, as i am only assigned this pc, i have to get this to work here as well.

Thank you in advance !

Your best bet is to invalidate caches and restart. Solves 99% of problems like this for me.

You can also try to reimport the project using the gradle tool window ...

Click the reload button here ...