Intellij Cannot resolve symbol on import

You can try invalidating the cache and restarting IntelliJ, in many cases it will help.

File -> Invalidate Caches/Restart

There can be multiple reasons for this. In my case it was wrong source root issue. Invalidate caches didn't work along with other solutions.

Check your module source roots.

1. Project Structure (Ctrl+Alt+Shift+S).

2. Modules

3. Select your problem module.

4. Change tab on top of window "Sources".

5. Remove unwanted source roots. Keep one and add src and test source roots in this root.

File -> Invalidate Caches/Restart And Build your project

IntelliJ has issues in resolving the dependencies. Try the following:

1. Right click on pom.xml -> Maven -> Reimport
2. Again Right click on pom.xml -> Maven -> Generate sources and update folders

Run this command in your project console:

mvn idea:idea 

Done. Had this issue many times. Tried 'Invalidate Cache & Restart' and all other solutions. Running that command works perfect to me. I'm currently using IntelliJ 2019.2, but this also happened in previous versions and solution worked as well.

File -> Invalidate Caches/Restart or rebuilding the project did not work wor me.

What worked for my Gradle project was to "Refresh all Gradle projects" from the Gradle tab on top-right corner of IntelliJ v2017, using the yellow marked button shown below:

Check your module dependencies.

1. Project Structure (Ctrl+Alt+Shift+S).
2. Modules
3. Select your problem module.
4. Change tab on top of window "Dependencies".
5. Check what needed library (maybe, you need to add specified library in the tab 'libraries') or module has listed here and it has right scope ('complile' mostly).

I faced a similar issue, Mike's comment helped me move in the direction to solve it.
Though the required library was a part of the module in my project too, it needed a change of scope. In the module dependency, I changed the scope to "Compile" rather than "Test" and it works fine for me now.

Had the same problem till I noticed that the src folder was marked as root source instead of java! Changing to only the java (src/main/java) to be the source root solved my problem

I found the following answer from @jossef-harush and @matt-leidholm useful from another link

• in IntelliJ editor, click on the red keyword (Integer for example) and press ALT + ENTER (or click the light bulb icon)
• select Setup JDK from the intentions menu

• click on Configure

• In my case, the JDK path was incorrect (pointed on /opt/jdk1.7.0_51 instead of /opt/jdk1.7.0_65)

• click on the ... and browse to the right JDK path

• let's clear the cache

After a long search, I discovered that a dependency was somehow corrupted on my machine in a maven project. The strange thing was that the dependency was still working correctly in the compiled java code. When I cleaned and rebuilt my maven dependency cache however, the problem went away and IntelliJ recognized the package. You can do this by running:

mvn dependency:purge-local-repository 

Intrestingly, the source of my problem hence wasn't IntelliJ, but maven itself.

I also got this error for multiple times when I try to build a new java project.

Below is the step how I got this stupid issue.

1. Create an empty project, and create new directory src/main/java.
2. Create the source package net.gongmingqm10.sketch.
3. Use gradle wrapper, gradle idea to build the gradle stuff for the project.
4. Add some dependencies in build.gradle file, and gradle build, reimport the project.
5. Create User.java and School.java in the existing package net.gongmingqm10.sketch
6. I got the error while I try to use import School in User.java.
7. Intellij keeps complain can not resolve symbol on import.

Solution:

Build the project first, and mark the main/java as the source root. Create a new directory with the same name net.gongmingqm10.sketch. Move all the files from the old troubling packages to new package.

Root cause:

Directory tree of source code

As you can see from the tree. I got a directory named net.gongmingqm10.sketch. But what we really need is the 3 levels directory: net->gongmingqm10->sketch

But before I finish building my project in Intellij, I create new directory named net.gongmingqm19.sketch, which will give me a real directory with the name net.gongmingqm10.sketch.

When we trying to import it. Obviously, how can intellij import the file under the weired directory with the name a.b.c.

@Anton Dozortsev I was driven crazy by a similar behavior; I ended up re-installing the IDE a bunch of times, only getting past the issue after removing the IDEA app, all caches, preferences, etc.

I tried all kinds of steps in the interim, (like restarts, invalidations, deleting .idea and *.iml files, and others.)

Turns out, the problem was due to IntelliJ's idea.max.intellisense.filesize setting. I had set it to 100KB, which was smaller than my dependency's size, leading to IntelliJ showing it as unknown, just like in your screenshot.

Fix:

1. Click on Help -> Edit Custom Properties

2. Set the property to a larger value; the default is 2500KB idea.max.intellisense.filesize=2500

Right click on pom.xml file, go to Maven click on Reimport. I had similar problem and this worked for me.

For 2020.1.4 Ultimate edition, I had to do the following

View -> Maven -> Generate Sources and Update Folders For all Projects

The issue for me was the libraries were not getting populated with mvn -U clean install from the terminal.

Try cleaning maven from upstream by:

mvn -U clean install 

I found the source cause!

In my case, I add a jar file include some java source file, but I think the java source is bad, in Intellij Idea dependency library it add the source automatic, so in Editor the import is BAD， JUST remove the source code in "Project Structure" -> "Library", it works for me.

Please try File-> Synchronize. Then close and reopen IntelliJ before you invalidate.

Once I restarted. I would have invalidated but the synchronize cleared everything after restarting.

Nothing I tried above worked for me (not that I tried every suggestion). What finally did the trick was to rename the class -- I just added a 2 to the class name and filename. Then I resolved all the references manually. (Since they weren't recognized, the refactoring did not change the references automatically.)

Once the "2-version" was happily resolved everywhere, I was then able to refactor and remove the 2 from the class and file, and everything was then as it should be.

in my case the solution was to add the project as maven project, besides the fact that i imported as maven project :P

go to pom.xml -> right click -> add as maven project

Faced similar issue, I Updated Intellij and error start coming - Can't Resolve Symbols.

Went to Plugins, Updated the plugins & Restart Problem Solved !!

I have had this issue multiple times, specially when importing a new project. In my case, there are projects based on spring-boot that includes multiples dependencies that causes Intellij to go mad the first time you import it.

As other answers here are valid, to know which one will suit better in your case, first check the log on Intellij:

~/.cache/JetBrains/IntelliJIdea202X.X/log 

Where the folder must match your current Intellij version. Here in some cases I have noticed some issues with some plugins that are causing some exceptions (in my case Checkstyle). Disabling the plugin, and invalidating the cache and restarting has solved the issue.

In other cases, I notice the classical:

Caused by: java.lang.RuntimeException: java.lang.OutOfMemoryError: Java heap space 

On the logs, but it is not reflected on the Intellij UI.

Where increasing the heap memory of the project on Intellij settings Build, Execution, Deployment -> Compiler -> Shared build process heap size can solve it as commented in others answers

Last case, I have a:

SEVERE - #o.j.i.maven - java.lang.RuntimeException: java.lang.OutOfMemoryError: Java heap space 

That is more related to when Maven refresh the dependencies. If is the case, Change on Build, Execution, Deployment -> Build Tools -> Maven -> Importing -> VM options for importer: and set it to -Xmx2g or any other value.

Other example is Build, Execution, Deployment -> Build Tools -> Maven -> Runner -> VM options: and set it to -Xmx4g or any other value.

Other option sometimes is to delete the cache and configuration from Intellij. According to this link, Intellij uses some directories where the cache is stored. Remove the next directory when intellij is not running:

~/.cache/JetBrains/<product><version> 

And start it. Check now if it works.

In any case, remember to check the log or you can spent several hours by trial and error with all the answers posted here. I have put some memory settings that must be adapted to your machine specifications. Do not copy and paste it blindly.

Simple Restart worked for me.

I would suggest first try with restart and then you may opt for invalidating the cache.

PS : Cleaning out the system caches will result in clearing the local history.

What did it for me is to edit the package file in the .idea folder as I accidentally added sources to this jar library and android couldn't resolve it by deleting the sources line as marked in the b/m picture library error.

Then rebuild the gradle and bam problem solved.

I had the same issue and the reason for that was incorrect marking of the project's sources.

I manually created the Root Content and didn't notice that src/main/test folder was marked as Sources instead of Tests. So that is why my test classes were assumed to have all their test libraries (JUnit, Mockito, etc.) with the scope of Compile, not Test.

As soon as I marked src/main/test as Tests and rebuilt the module all errors were gone.

I had this recently while trying to use Intellij to work on NiFi, turned out the issue was that NiFi requires Maven >= 3.1.0 and the version that I'd checked out with (I guess my default) was 3.0.5. Updating the Maven version for the project fixed it, so in some cases Maven version mis-alignment can be a thing to look...I'd guess it's fairly unusual but if you get this far on the thread you're probably having an unusual issue :)

file-> Project Structure -> Modules, find the module with problems, click it and choose the Dependencies tab in the right side. Click the green plus sign, try to add the jar or libraries that cause the problem. That works for me.

My issue was my Maven plugin got disabled after an update. I went to Help -> Find Action... -> Typed in Maven and found that it was "Off". I clicked the toggle switch and after a bit of loading it was re-enabled.

Also, check your class is not in compile exclusions

If you see, that there is a little grey cross in left top corner, you must remove class from compile exclusions

How to remove