Intellij IDEA how to return error underline?

Question

IntelliJ IDEA

Hello, IDEA has stopped underlining errors with a red squiggle and showing light bulb messages. How to return these properties?

Answer 1

Idea will behave like a regular notepad until it realizes that you are working on a "project".
In File -> Project Structure, you need to configure the SDK for the project and the Language Level
. Also, you may need to specify folders with sources, tests, and resources.
Idea can do all this automatically by importing maven or gradle projects.