Develop Reference

IntelliJ IDEA is not recognizing my java files as runnable and instead wants to run the class files. Any ideas of how to fix?

Anytime I try to run a java file by clicking run, it instead tries to run the class file and thus gives a no main method error.
When I try to right click on a java file and run that, it doesn't recogize it as a file that is runable.
I am still able to run programs from the command prompt but I would prefer to be able to run them in IntelliJ.
This occurred after trying to create a Class path when using JSon Libraries.
Edit:
Normally it shows java files with this icon:
But instead it's showing this icon for java files:
I think the change in icon might have something to do with it.
Edit 2:
the exact error I get is "C:\Program Files (x86)\Java\jdk1.8.0_181\bin\java.exe"...bunch of other program file locations
Error: Could not find or load main class sample.Main
Process finished with exit code 1

I had the same problem and found out that my src wasn't marked as Sources Root. To change this:
right-mouse click on your src
navigate to "Mark Directory As"
choose "Sources Root"
It will now recognize your files correctly and your main classes will be able to run again
IntelliJ not recognizing my .java-files
Problem solved

I had a similar problem.It wouldn't pick up ModlServer in any project. (Not just limited to the one I had open).
I had to file -> Manage IDE Settings -> Restore Default Settings
Note: I lost all my live templates, fonts, etc so just a heads up.

I restarted my computer and that somehow fixed it.

My issue was that I have multiple modules for my project and the module I was working on (where java files were not recognized) was not included in the main pom. I just added that module in the main (project) pom and it worked.

Right click on the project and click 'Add framework support' all directories and classes should now be the right type.

I've fixed this at Intelij2023 by using JDK17 as the JDK the IDE uses to import java source files.
Mind this JDK version does not need to be the same you use to build your project.
Go to: Settings > Build, Executio, Deployment> Build Tools > Maven > Importer
Set the JDK For Importer to zulu-17
I'm using zulu-17 as JDK for imports and coretto-8 to build the project (having JDK version 8 seems to be preventing intelij to properly recognize the project structure)

If you are using Maven or Gradle, try to re-import the project and see if that helps. Could be that your IDEA project has some incorrect settings in it set by mistake, so this way those would be removed.

How to save Java Project from IntelliJ IDEA to Git repo so it will build on another PC after cloning?

I'm building a simple calculator app from a tutorial/class on Pluralsight (Java Fundamentals class), which starts with a Main.java file, and adds a class file later, MathEquation.java.
I created a Git repo to track my progress, and uploaded to Github: JavaFundamentalsClass. I used GitIgnore.IO to find a Java IntelliJ .gitignore file, and everything seemed to be working fine on the original PC I was using.
However, after switching over to a different PC, with a fresh install of IDEA, I cloned down the repo from Github, and found that the project would not build and/or run. I get this error:
"C:\Program Files\RedHat\java-1.8.0-openjdk-1.8.0.191-1\bin\java.exe" -Dfile.encoding=windows-1252 -jar ""
Error: Unable to access jarfile
Process finished with exit code 1
I suspect that there is something in the .gitigore file that is keeping some of the project, dependency, or build information from being saved in the repo that keeps IDEA from having all the info it needs to build and run the Main.java correctly.
Can anyone help? You should be able to download the project from the repo linked above in it's currently broken state, including the .gitignore file.
Additional Info
I wiped my repo clean and recloned and I forgot, originally it doesn't even give me the run button (it is grayed out). I had to do a procedure with "Add Configuration" from a search I did for that to show up to get the error above.
Also, I did install java from the OpenJDK, rather than oracle. I figured with Oracle cutting off commercial development maybe start the switch now as I'm learning, but maybe that's the issue (normal Java on my other PC).
It's working, but...
First thing - Intellij needs to know where Java is. It appears that if the SDK/JDK is not installed prior to Intellij, you will need to tell it where Java is after installing. Or if you use OpenJDK instead of Oracle Java SDK. You can do that at View/Open Library Settings, under Platform Settings / SDKs (select the JDK home path).
Then, after setting up Java, I am able to get everything working in Intellij IDEA if I find the Main.java file, right-click, and choose "Run main.main()". This runs the program okay, and also creates a Main configuration in the Run/Debug configuration area, and finally the "Run" button becomes available.
So I can get it working, but if I wipe all the files and clone it fresh from the remote repo, I have to go through running the Main.java file directly again to recreate the configuration.
So, this still doesn't answer my original question. Why doesn't this configuration get saved in the repo? What file is this information saved in? Is there something in the .gitignore file that is keeping this information from being saved to the repo?

Look like you have a different java version on your second machine.
First of all, check your java version
Update the configuration of your project, right now it pointing to java 1.8
https://github.com/LightCC/JavaFundamentalsClass/blob/master/.idea/misc.xml

I think it might be because of java not installed on the other PC you were trying. If it is installed just check whether the path mentioned has java executable file.

The first part is ensuring Java is setup, and that Intellij IDEA knows where Java is, per the other answers, comments, and addendums to the question.
The second part is setting up the run/debug configuration, per the "It's working but.." section of the question. This can be created automatically by right-clicking the file that has the main class to be run (usually Main()...), and selecting the "Run Main.main()" option (replacing Main and main() with the file and function which needs to be run)
The final piece is that to get the run/debug configurations to save to the repo, you either need to:
Share the workspace.xml file (i.e. make sure this is not in the .gitignore file). However, there is a lot of user-specific stuff in that file, so it should normally be excluded from the repo.
Or, edit the configuration and checkmark the "Share" box in the upper right-hand corner (just right of the "Name" field). This will put the configuration into a separate folder inside the .idea folder, which should not be excluded from the repo by .gitignore.

finding changes eclipse makes to maven project

I have a maven project which I have downloaded from this link. When I make a couple changes to it, it runs perfectly from the command line when I type:
mvn clean install tomcat7:run-war -Dmaven.test.skip=true
in the directory to which the zip was extracted. (The only 2 changes required to make it work on the command line are to 1.) add a plugin tag for tomcat 7 in pom.xml and 2.) create a context.xml file in the webapp/META-INF folder. Everything else in the app remains the same as the github verion, and the app runs fine from the command line using the command given above and then typing the url in the browser.)
However, when I import the project into eclipse as an existing maven project, and then try to run the app, the app starts throwing errors related to not finding a couple of jars which are clearly in the repository. The app no longer compiles from the command line, or from eclipse. I even tried to run the app as a maven build from eclipse and even changed the maven instance eclipse uses to the freestanding maven that works from the command line instead of the embedded maven in eclipse, but the app still threw the same errors when I tried to run it.
But then, when I repeated the steps with a fresh copy of the app, the fresh copy runs fine from the command line, while the copy that eclipse touched does not compile by any method.
It seems that eclipse has made some changes to the app in the process of importing it as an existing maven project into eclipse. How can I locate the specific changes that eclipse has made to the app? I would like to be able to use eclipse as my IDE, but I cannot do so unless it can compile the code.

This answer was originally posted as a comment it turns out that resolved the OP's problem, and as He asked I'm turning into an answer.
First set your eclipse to use the JDK instead of the JRE. Just as a reference this configuration on Eclipse is Normally on Window->Preferences...->Java->Installed JREs:
Second (as you already did) change eclipse maven to look at installed maven that runs on the command line again.
I've encountered some problems with maven running with the JRE instead of the JDK. Try it and let me know. I will sleep now. Tomorrow I will see what happened.

Error: Archive for required library cannot be read or is not a valid ZIP file.

I am having trouble setting up the build path of my java project. I am currently in a Co-Op IT position so I am somewhat new to all this. My background is mostly in C++ and I am learning java on the fly. I am also somewhat new to Eclipse (Kepler service release 1).
I am working on a bug on an existing program and need to get the program to build so I can work on it. When I add all of the external .jar files that I know for a fact are the right ones, I am getting this error on two of them :
"Archive for required library: '(location of file)' cannot be read or is not a valid ZIP file"
Two of the other full time guys on my team have gotten the program to run with those exact same .jar files, one running Eclipse Indigo and the other running the same Kepler version as myself. I also was able to open the two .jar files manually and everything appears to be there. After every trial trying to fix this, I have refreshed, cleaned and restarted eclipse. The two other full time guys said they have never seen this error. I would like to get some insight on this from anyone who has any similar experiences so that I don't have to use up much more of their time.

I Had this issue, just fixed by deleting .jar files from Libs directory then copy->paste original Jars again. Then do a complete clean -> rebuild

I got this problem, took help from following link solution
which basically says to
1. delete the corresponding maven download folder
2. maven>update project in eclipse
In my case I deleted hibernate folder, since i was getting error related to hibernate-validator.jar

I had the same error here. What I did to resolve the problem was close and reopen the project.

I got the same problem and found out the root cause is the JDK in my linux shell is set to 1.6, but in the eclipse, the JRE is 1.7.

Using Eclipse without m2e features (Standard Edition) helped me.
Similar problem with Spring toolsuite

Just came across this link that shows a way to get unblocked.
In preferences dialog box go to
Java->Compiler->Building
and change Incomplete build path to "Warning" (from default "Error")
This can be done globally (for all projects), or on a project by project basis.

Check the jar's file permissions/ownership.
I had the same issue on eclipse installed on Linux and fixed it by setting the file permissions right.

In my case ..worked after removing this from spirngrest-servlet.xml file.
<prop key="net.sf.ehcache.configurationResourceName">/Sysehcache.xml</prop>
I think it had to do with default location of maven repository of jar files.
Been at it for 3 days. finally solved it.Hope it helps anyone.Just look for similar think in your spirngrest-servlet.xml file. Good luck.

I just tried the following and it worked:
Close eclipse as there might be some files eclipse is accessing and you won't be able to delete.
Delete all the libraries installed in the maven repositories folder: ".m2/repository"
Open eclipse and update your project(Alt+F5).
What did we just do? : This is possible that the existing libraries in the local repository are erroneous and maven tries to open which it fails in. We have now deleted the already existing library and with the project update, Maven will download the library again which should resolve the issue.

i fixed this by just deleting everything inside of the /Users/username/.m2/repository folder. not the repository folder itself. and then running a mvn clean package in the project folder

RCP's exec launcher can't find companion shared library on launch, but starts with click on org.eclipse.equinox.launcher_1.2.0.v20110502.jar

I'm building an Eclipse RCP application against Eclipse 3.7.1 and Java 1.6.
I'm also using Tycho to build, and have set up my RCP according to the Tycho tutorial from the EclipseCon 2011, to which I've stuck slavishly, apart from project names.
The application builds fine up until I get to Step 5 (adding a p2 repo, then adding a .product file. Well, it still builds fine, and everything is where it should be, but I cannot start the RCP by clicking on the .exe file from the repository in the workspace.
All I get is the old dreaded "The [RCP] executable launcher was unable to locate its companion shared library" error popup.
First of all I thought I might have set up the CLASS PATH incorrectly, but when I open a console and type javaw or java -version anywhere, it all works.
Also, when I go to the pluginsfolder in the p2 repository for the RCP in the workspace, and double-click on org.eclipse.equinox.launcher_1.2.0.v20110502.jar, the RCP starts, albeit without the splash screen.
This must surely mean my Java set up is correct, and it's not a class path problem?
I'm not sure where this problem might lie (I have a plugin, a feature, a product, a repository, and a parent package with the main pom), so if you let me know your suspicions where the error might come from, I'll be more than happy to post respective XML, build.properties, screenshots and what have you. Unless this is a common error with a common solution.
Many thanks in advance!
Oh yea: Windows 7 (64-bit), JDK and JRE both 64-bit as well, Eclipse EE 3.7.1 (I chose that because it contains the most plugins I'll need later by default).
UPDATE
I'm attaching my CLASS PATH Settings for reference.
User variables
CLASS PATH: C:\Program Files\Java\jdk1.6.0_30;.;
System variables
JAVA_HOME: C:\Program Files\Java\jdk1.6.0_30
Path: %JAVA_HOME%\bin;
UPDATE 2
When I let Tycho create a ZIP file in the p2 repository, and copy that from the repo to another location, unzip it and run the .exe, the application starts without problems. So I guess this query is partially solved, but I'd still be interested to hear why I wouldn't be able to start the application from the repository...

Today I came across the same issue. I guess you could find the solution here: https://bugs.eclipse.org/bugs/show_bug.cgi?id=176084
In short, the problem in my case was, that the org.eclipse.equinox.launcher_1.2.0.v20110502.jar must be unpacked in the plugins folder under the folder name: org.eclipse.equinox.launcher_1.2.0.v20110502
... hope that helps!

In my case the error The [RCP] executable launcher was unable to locate its companion shared library was because my path was too long.

Same issue I was facing from yesterday. Today, I have changed path of project(git clone) and build it and able to run RCP executable.
I think this issue was because of path too long.