IntelliJ: cannot find java.util.Optional

I had a similar problem in ubuntu. For me the problem was that I used JDK1.7 and when I changed it to JDK1.8 everything worked just fine.

Now, that makes sense, as Optional is something that was introduced in JDK1.8, before that the concept was exists only in Guava: http://onelineatatime.io/optional-guava-and-java-8/

Ran into the same problem (in IntelliJ 2017.2.7) and solved it like this: Project Structure->Modules->Module SDK and there change it to 1.8

I've also first set Java compiler to 8 and Project Structure->Project->Project SDK and Project language level also set to 8 without success. In the end, the step I described finally fixed it.

I finally figured this out. For whatever reason, there was an entry for java.util.Optional in the exlusions under Editor, General, and Auto Import.

Removing that did the trick. No idea how or why it ended up being there. Doesn't sound like anything I would want to do.

Stupid IntelliJ.

I have a SpringBoot project which worked just fine. Then, the next day, when I want to run it, I got this error: Caused by: java.lang.Error: Unresolved compilation problem: The type java.util.Optional cannot be resolved. It is indirectly referenced from required .class files without changing anything!

• I cleared IntelliJ cache.

Although it was a maven project it was already using JDK8,

• I have changed the Project Settings, and said (again) to use JDK8,
• Maven re-import, Cleaned the project, Build->Rebuild project, and it magically worked again