1. JDK download

2. setting IntelliJ JDK

File → Project Structure → Platform Settings → SDKs → add JDK

3. setting project JDK

File → Project Structure → Project Settings → Project → update Project SDK

4. create Module

File → Project Structure → Project Settings → Modules → + → select added JDK

Whether exsting modules, delete and create module to create .iml file.

ps) refresh project

If not apply, delete .idea folder, write code and reopen the project.

According notice, define JDK.

5. add Configuration

To start project, add configuration.

+ → Application

essential setting

1. Name
2. JDK
3. Main Class