How do I fix a “declared package does not match the expected package” error on VSCode

I have a gradle project:

.
|-- src
|    |-- java
|    |    +-- myproj
|    |         +-- App.java
|    +-- test
|-- build.gradle
+-- ...

and App.java file looks like this:

package myproj;
//      ^^^^^^ error message

but VSCode tells me “The declared package "myproj" does not match the expected package "main.java.myproj"”. I know this is related to the file path, but I did not find out how to configure it.

I have installed the Java Extension Pack plug-in, what should I do next?

PS. I don’t want the configuration scheme to be too complicated, I’m just writing a very small program. It is best to be able to complete in setting.json.