Develop Reference

"Cannot resolve symbol" in Intellij IDEA

I'm fairly new to Intellij and Java and am unable to use libraries from one "module" in another. I am seeing red class names and getting "Cannot resolve symbol ..." errors all over the place:
The other modules are referenced in File | Project Structure all the other module's Paths are correct and include the *.classes I'm trying to use:
I have also tried a File | Invalidate Caches but am still having the same problems.
What do I need to do to fix this?

Listed below are steps which may fix the problem:
1.Invalidate and refresh the IntelliJ's caches
File Menu -> Invalidate Caches / Restart -> Invalidate and restart
2.Project SDK selection
Check project settings from File Menu -> Project Structure
Ensure an SDK is selected for the Project SDK. If is selected, click the 'New' button, select JDK and then select the correct path to the JDK e.g. /opt/java/jdk1.8 or c:\Java\Jdk1.8
3.Corrupt JDK
There may be a problem with your JDK installation, re-install JDK
4.Re-import the project
Close the project if it is open in IntelliJ
Delete the .idea folder in the project source code folder.
Start IntelliJ and Import the project.
You can choose any of them which will work for you.

I faced a similar problem for no reason, I think it was caused by IDE(android studio). I have tried all of the above solutions but not worked. Finally, in my own situation, I solved this problem by the following actions:
Delete your .idea folder in your local project.
Reopen this project and just let Gradle run itself.
It was worked for me. I hope that my experience will be useful for you.

You need to add your external libraries/classes under dependencies in order for IDEA to see them when doing code analysis/autocomplete.

You can go to "File->Project Structure"
From "Project Settings", Select "Project" tab and there make sure that "Project SDK" has proper JDK selection.

After you add dependencies to POM file, make it a habit to refresh POM by clicking on the 'Reimports maven projects' icon. Its the first icon in the maven tool window located to the right of the main intellij editor. Its a blue icon with 2 circular arrows. Clicking it ensures that the added dependencies are fully integrated into your project

Run it from the project's root folder.
$ mvn -U idea:idea

One more advise would be to make sure that you import the project properly. If it's a maven project, import pom.xml and if it's a gradle project, import gradle.build file to make sure that all the dependencies are downloaded correctly.

Just got this.
Just went there.
Invalidated the cache.
Seemed to work until I wrote further lines.
Then noticed that I was writing my code outside of the main() function.
Moved the ending curly bracket further and voila.

Null Pointer Importing Gradle Project Into Eclipse

I used libGDX to generate some gradle projects that I now need to import into Eclipse. So, I opened Eclipse, installed the gradle plugin, and went to File -> Import -> Gradle Project.
At that point, I chose the directory that contained my generated gradle projects. Then, I clicked 'Build Model' and then added my projects to the list of available projects to import. After I select 'Finish' Eclipse begins importing them. Right at the very end I get this dialog:
Looking in the log file, I found this stack trace:
java.lang.NullPointerException
at org.springsource.ide.eclipse.gradle.core.wizards.GradleImportOperation.refreshProjects(GradleImportOperation.java:256)
at org.springsource.ide.eclipse.gradle.core.wizards.GradleImportOperation.perform(GradleImportOperation.java:195)
at org.springsource.ide.eclipse.gradle.ui.wizards.GradleImportWizard$1.doit(GradleImportWizard.java:66)
at org.springsource.ide.eclipse.gradle.core.util.GradleRunnable$1.run(GradleRunnable.java:49)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:53)
I've tried reinstalling everything relevant. I've created the projects several times. I've downloaded a fresh version of eclipse. But, the same issue occurs everytime. Any help would be great. Thank you.

In case it helps someone else in the future, I had the same problem, but a different resolution. My issue was resolved when I moved the projects out of the eclipse workspace directory. It can be in another directory entirely, or in a subdirectory.
BROKEN:
/path/to/workspace/.metadata
/path/to/workspace/build.gradle
/path/to/workspace/core
/path/to/workspace/etc
WORKS:
/path/to/workspace/.metadata
/path/to/workspace/projects/build.gradle
/path/to/workspace/projects/core
/path/to/workspace/projects/etc
I did not need to remove the "afterEclipseImport" script. See this issue: https://github.com/libgdx/libgdx/issues/1537#issuecomment-38535167

As it turns out, when importing a gradle project, there is a field called "Run After" which defaults to "afterEclipseImport". This doesn't exist unless it is defined in the project you are importing. The documentation says that if it doesn't exist then the gradle import project skips over it. Well, once I unchecked this option, the import worked correctly.
Edit: Just as an aside. This assumes that your project is in a subdirectory inside your workspace as opposed to the workspace directory itself. (See the other answer).

I had a similar problem with eclipse 2019-03 and gradle 5.3.1.
In the end I created a new workspace and I was then able to import the gradle project.
Originally I had a workspace and tried to create a second gradle project from within eclipse but it failed trying to synchronise with gradel.
I also tried moving the project out of the workspace dir but it still refused to import.

Error when importing an existing project to eclipse

So I'm trying to import an existing project to eclipse and when I do I get the following error. The main folder of the project in the package explorer has a red exclamation mark (!) next to it and console says the same error 3 times:
[2013-07-10 14:23:39 - Myproject1] Project has no target set. Edit the project properties to set one.
[2013-07-10 14:23:39 - Myproject1] Project has no target set. Edit the project properties to set one.
[2013-07-10 14:23:39 - Myproject1] Project has no target set. Edit the project properties to set one.
I did my research on this error and found a bunch of stuff on this website already but nothing helps. People are mostly getting this error when they try to execute the imported project, not as soon as they import it. I also tried setting the "target set" in the project properties, as the error tells me to, but I can't find where to set the "target set" anywhere in the properties.
One more thing worth mentioning also, if I open the src folder and try to open any of the *.java, everything is blank, the "code" opens but it's blank. Any help would be greatly appreciated!

The file 'project.properties' is missing. It must reside in the root-folder of your project.
( Where the AndroidManifest.xml is located )
You should create a new android-project and import the sources and resources
OR create it manually.
Example content for project.properties:
# Project target.
target=android-17
Greetings
Christopher

set android target version on your project manifest xml file or eclipse ->right click project click properties->select android tab->check latest android version on the list like below screen shot:
after click ok button will apply wait some seconds after your issue will be solved!

you should try fixing project properties:
rightClick on Project -> Android Tools -> Fix Project Properties.
That resolved my issue!

You are probably importing your project folder on your workspace. In my case, i got that same error, so i just move the project folder to "C:" and tryed to import again. And bingo!

Netbeans compiles fine but show errors in editor

Netbeans is not importing a jar from another project. The classpath is fine, the project compiles fine but the editor show several errors in project because it cannot locate classes inside that jar. I've already rebuilded the projects and clean Netbeans' cache (~/.netbeans/7.1.1/var/cache/)
Netbeans version: 7.1.1 and also 7.0
OS version: MacOS 10.7.3
The problem lies with the Netbeans' code editor. My project compiles and it's packaged just fine. I have no problem on that. I have this annoying error messages (eg. red background) in the code editor with no reason.
A workaround I just found: Renaming the dependency project (with refactoring) and adding the new jar to my project do the trick. Still I don't know what happened.

I just had the same problem in NetBeans 7.2.1 today. I could build the project fine but got error markers in the source files and in the Projects tree listings. It seems as if the compiler when you build a project uses a different classpath from the compiler that works in the edit window.
In my case I found we had the same package and class names for different classes in different jars. I don't know if this is relevant or just a red herring.
I still had an error in one project that used these two jars. It seemed like it could only see the classes from the second jar listed in the pom.xml file (we use Maven). I commented out the second jar & rebuilt, then uncommented that second jar & rebuilt and suddenly all of my errors went away.
So I don't have a definite solution but removing and reintroducing a dependency worked for me.

How you import jar file ? You have to right click Libralies in Project Panel and click Add JAR/Folder. And select jar file which you want to import.

I think you have wrongly imported the jar file. Try out the below steps to add jar(s) to your classpath properly.
1. Select your project from the Projects explorer.
2. Right click -> Properties.
3. Select Libraries from Categories list.
4. Click on Add JAR/Folder button.
5. Add your jar(s) & click on OK to finish the process.
Now, it should resolve the reference issues

You mentioned, the editor shows errors because it cannot locate classes inside that jar. Well, are you sure you are using the right jar or right version of jar ? Eclipse is not able to locate any of the classes or only few classes ?

I wish my answer would help fixing the issue (even if too late :) )
Indeed, I have a maven project with two modules. Module1 that contains the class com.x.y.MyClass and Module2 where I'm trying to import com.x.y.MyClass.
It compiles fine, and I can run unit tests using netbeans, but the errors in the editor were embarrassing. So I add Module1 version and packaging type to the pom.xml of Module2 and that fixed my problem (I know, it's very bad to hard code a module version, but at least, I can work without worrying about the editor list of errors)
Cheers !

This is definitely too little too late, but I had this problem today with Netbeans 7.2. All jars were in place, the code was compiling from the build menu, but Netbeans was marking the files in error.
The same exact project was compiling fine with Netbeans 8.0.1.
The problem was with the "Source Root". I clicked on menu Window -> Debugging -> Sources (Alt+Shift+8) and I noticed that I had specified sources on some of the jar dependencies of the project that were no longer valid. Cleaning them up was a 2 step process:
Clean them up from the project files in nbproject dir
Clean them up from
%APPDATA%\NetBeans\7.2\config\Preferences\org\netbeans\modules\java\j2seplatform\Sources.properties
After clean up, I restarted Netbeans and everything was OK.
Hope this helps someone.

I had this issue with few jsf xhtml pages though there wasn't any error in the content of the page. So I opened each page and cut all content, saved the empty file then paste back all content and saved it. it solved the red marking error symbol for me.

I know this question is a bit old but for those who may be facing the same issue currently, hope this will help.
I faced the same challenge after moving my maven projects to a new directory. To fix the issue, I just simply
Renamed the new folder(the one containing my maven projects) just the same name as the previous folder.
Reimported the projects in Netbeans.

Eclipse says my Android project(s) contain(s) errors, but there aren't any

Since last night, Eclipse hasn't been letting me run any of my projects and gives me the error "Your project contains error(s), please fix it before running it".
This happens regardless of which project I use.
There are no code errors in any projects
There are no missing files (R.java, etc.) or folders (src, res, etc.)
There are no errors in the console (even on verbose) or the error log screen
I've cleaned all the projects, and each individual project many times
I've restarted ADB, Eclipse, and my computer
I have no idea what to do next, so hopefully its fixable.
NOTE: I am using Git, and this occurred after switching to my master branch to export a new update to one of my apps.
Thank you in advance! (:
Edit 1: I have also tried deleting and re-importing the projects before I posted this.

Click Window -> Show View -> Problems, that should show what exactly Eclipse thinks is wrong with your project. Sometimes you can simply delete the problem from that view, and Eclipse believes you everything is fine (yep, weird, I know).
Also, after you switch branches using an external source control tool (one not integrated into Eclipse through a plugin), Eclipse sometimes won't pick up all changes, you'd need to manually refresh the whole project file tree.
If nothing else helps, try setting up a new Eclipse workspace and importing your project there.

check your build paths - there could be jars and dependencies that are outside of the app that need to be opened or imported.
another trick is to edit an xml file, just change one word to intentionally cause an error, save the file, then change it back to proper syntax and save again. Error magically disappears.
another trick is to edit a java file, (cause error, save, fix error, magically error free)

I had this problem and I have fixed it. My issue was this:
I somehow managed to require another project in my build. That project had errors in it, which I believe is what caused the issue. I think this happened when I accidentally asked Eclipse to fix my build path or something when I was trying to fix a mistake. To correct this issue go to (on mac):
Right click on your project folder in the Package Explorer
In the menu, go to "Build Path"
Select "Configure Build Path"
Go to the "Projects" tab (along the top).
Is there anything in there? If there is and you weren't expecting there to be, select the project that is in that folder and hit "Remove"
This fixed the issue for me. Hope it helps.

I think you need to clean your project. Do project -> clean. Should work fine after that.

Try using Project->Android Tools->Fix Project Properties besides checking for your Android path. Check if your ANDROID_HOME and ANDROID_SDK are set correctly besides adding tools and platform-tools are set correctly in environment variable PATH.
Hope this helps!

Go to your .android folder and delete your debug certificate.
E:\Users\(your profile)\.android
Inside that folder there is a file name 'debug.keystore'. Delete that, clean and try to build the project again. Sometimes this error is caused when the certificate expires.
I found this answer here and it solved my problem ;-)

I think go to project ->clean some error can be solve this problem

Go to Projects in the menu bar
Then check the menu Build Automatically.
This helped for me.