No "out" folder when running the idea#
Error occurs when running the project#

Actually, this error is caused by not setting the output path. You just need to modify the settings in two places:
- 
Click "File" in the upper left corner of idea.
 - 
Select "Project Structure".
 - 
Check "Inherit project compile path" in the Modules settings.
 

- Set "Project compiler output" in the Project.
 

- Select "Project path" + "\out", for example, mine is D:\ideaproject\javaSE\out.
 

After making these two changes, you will be able to run normally.