Unable to run Java code with IntelliJ IDEA

Question

I have just downloaded the IntelliJ IDEA, and I want to edit my first Java file with it, I'm not interested in creating a whole project, just editing the single file.

So I opened the file from my desktop with Intellij IDEA as I set it as my default program for opening .java files.

I write some code and the main run and debug buttons are greyed out! I can't run my code!

I have already installed Java 8 update 45 64-bit (I have a 64 bit OS) as well as the Java Development Kit (J8U45). I have set my global IDE SDK as my JDK installation, and when it prompts me I also set this as my project SDK, but still the run and debug buttons are unable to be used!

Edit 1:
I am also unable to run my file regardless of if its in a project or not.

Edit 2:
Screenshot of my project setup.

Create a project, then create a Java module. Put your class there and execute it. If you only want/need the IDE for editing the Java file, edit the file accordingly, then compile it using `javac` and execute the class using `java WhateverTheNameOfYourClass`. — Luiggi Mendoza, Jun 18 '15 at 19:19
I also tried that, but when I did I was unable to create a Java file, the closest is a Java class file (its a small project so I will only need one file and not multiple classes) and it said unable to create class-file. — Adam Griffiths, Jun 18 '15 at 19:19
Try adding a source root in your project. Put your java file under that — vikingsteve, Jun 18 '15 at 19:23
What is javac? It seems weird that I have to compile my program every time I want to run it, with other programming languages I've been able to run the code in the IDE on the fly without compiling it. I have also put a source root in and it still won't let me run the file. — Adam Griffiths, Jun 18 '15 at 19:25
Are you sure you have a Java **Module** and that the proper JDK is configured in this **Project**? — Luiggi Mendoza, Jun 18 '15 at 19:25
[javac](http://docs.oracle.com/javase/8/docs/technotes/tools/windows/javac.html) — Luiggi Mendoza, Jun 18 '15 at 19:25
Do I really need to compile my code every time I want to run it using javac? I thought the point was to be able to test code on the fly? — Adam Griffiths, Jun 18 '15 at 19:30

score 87 · Accepted Answer · answered Jun 18 '15 at 19:33

87

Move your code inside of the src folder. Once it's there, it'll be compiled on-the-fly every time it's saved.

IntelliJ only recognizes files in specific locations as part of the project - namely, anything inside of a blue folder is specifically considered to be source code.

Also - while I can't see all of your source code - be sure that it's proper Java syntax, with a class declared the same as the file and that it has a main method (specifically public static void main(String[] args)). IntelliJ won't run code without a main method (rather, it can't - neither it nor Java would know where to start).

answered Jun 18 '15 at 19:33

Makoto

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Done and I updated the screenshot to reflect the new file movement. However the run command is still unusable, you can't see it as I have not opened the menu so you can see my code instead. – Adam Griffiths Jun 18 '15 at 19:38
Be sure that you have the module for the project set to the Java JDK. Otherwise, try putting a break point on the only executable line in the code and enter debug mode. If that works, then you're capable of running the code (and if you do run this you won't get any output since nothing's being printed). – Makoto Jun 18 '15 at 19:51

score 80 · Answer 2 · edited Mar 22 '17 at 21:15

80

My classes contained a main() method yet I was unable to see the Run option. That option was enabled once I marked a folder containing my class files as a source folder:

Right click the folder containing your source
Select Mark Directory as → Test Source Root

Some of the classes in my folder don't have a main() method, but I still see a Run option for those.

edited Mar 22 '17 at 21:15

William Price

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answered Mar 22 '17 at 14:04

MamathaMacherla

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This should definitely be the accepted answer! Thank you! – Conjecture Apr 30 '20 at 09:17

score 36 · Answer 3 · answered Apr 07 '18 at 11:54

36

right click on the "SRC folder", select "Mark directory as:, select "Resource Root".

Then Edit the run configuration. select Run, run, edit configuration, with the plus button add an application configuration, give it a name (could be any name), and in the main class write down the full name of the main java class for example, com.example.java.MaxValues.

you might also need to check file, project structure, project settings-project, give it a folder for the compiler output, preferably a separate folder, under the java folder,

answered Apr 07 '18 at 11:54

Matthew E

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I think that "src" folder should be marked as "Source root" and not "Resource root". But other than that, that is the correct answer. – arenaq Nov 16 '18 at 01:23
Actually I found that `src/main/java` should be marked as the Sources Root. Then `src/main/resources` is the Resources Root, and `src/test/java` and `src/test/resources` are the Test Sources Root and Test Resources Root, respectively. – Ethan T Jul 15 '19 at 17:57
I cloned a project from Github and it didn't set the folder to source, so once I done it manually. Then I was able to configure the compiling options – testing_22 Jan 10 '22 at 22:59

score 13 · Answer 4 · edited Feb 05 '20 at 03:05

13

Don't forget the String[] args in your main method. Otherwise, there's no option to run your program:

public static void main(String[] args) {

}

edited Feb 05 '20 at 03:05

meyi

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answered Sep 11 '16 at 05:01

Ken Ratanachai S.

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The proper declaration of `main` is visible in the picture. – Makoto Jan 12 '17 at 16:30
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Those are really really really small and I didn't see that. – Ken Ratanachai S. Jul 09 '17 at 23:17
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You could've opened the image in a separate tab. It's definitely there, though. – Makoto Jul 09 '17 at 23:34
I am getting errors like To see the full stack trace of the errors, re-run Maven with the -e switch. [ERROR] Re-run Maven using the -X switch to enable full debug logging. – Azhar Uddin Sheikh Aug 25 '21 at 13:25

score 8 · Answer 5 · answered Sep 25 '19 at 07:25

I had the similar issue and solved it by doing the below step.

Go to "Run" menu and "Edit configuration"
Click on add(+) icon and select Application from the list.
In configuration name your Main class: name of your main class.
Working Directory : It should point till the src folder of your project. C:\Users\name\Work\ProjectName\src

This is where I had issue and after correcting this, I could see the run option for that class.

score 1 · Answer 6 · answered Jun 15 '19 at 21:54

1

Something else that worked for me:

Right click the folder in src containing your main
You'll see an option "run 'file.main()'" with the run icon.
Click it, and then the run icon in the top right and bottom left will turn green from then on.

answered Jun 15 '19 at 21:54

HappySpaceBoy

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score 1 · Answer 7 · answered Jul 18 '19 at 09:15

Sometimes, patience is key.

I had the same problem with a java project with big node_modules / .m2 directories.
The indexing was very long so I paused it and it prevented me from using Run Configurations.

So I waited for the indexing to finish and only then I was able to run my main class.

score 1 · Answer 8 · answered Jul 20 '19 at 08:48

1

If you can't run your correct program and you try all other answers.Click on Edit Configuration and just do following steps-:

Click on add icon and select Application from the list.
In configuration name your Main class: as your main class name.
Set working directory to your project directory.
Others: leave them default and click on apply. Now you can run your program.enter image description here

answered Jul 20 '19 at 08:48

Dipesh Chauhan

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where is this add icon? – Line Dec 20 '19 at 22:13

score 1 · Answer 9 · answered Apr 16 '20 at 20:39

Last resort option when nothing else seems to work: close and reopen IntelliJ.

My issue was with reverting a Git commit, which happened to change the Java SDK configured for the Project to a no longer installed version of the JDK. But fixing that back still didn't allow me to run the program. Restarting IntelliJ fixed this

score 1 · Answer 10 · edited May 23 '20 at 19:00

1

-First Move Your Code Files in side the "src" Folder

-Make sure your Main method is declared like the following

   public class Main {
         public static void main(String []args){


       }
    }

then:

Go to Project configurations
select Java application,
check allow parallel run
and select your main class

and it should work

edited May 23 '20 at 19:00

user254694

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answered May 23 '20 at 16:03

This was a good hint for me but it seems like this may be for a different version than I have but I'm not sure. I clicked an "Add Configuration" button near the top right of the app. From there I selected "Application" then filled out the project name and the specified the `main` class. I also checked the "store as project file" option (to save the settings, perhaps). After clicking Apply I am now able to run the project. Yay! – Nathan Mar 17 '21 at 01:26

score 0 · Answer 11 · answered Dec 12 '17 at 10:15

0

If you are just opened a new java project then create a new folder src/ in the man project location.

Then cut and paste all your package in that folder.

Then Right click on src directory and select option Mark Directory As > Sources Root.

answered Dec 12 '17 at 10:15

Niraj Kulkarni

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score 0 · Answer 12 · answered Aug 27 '19 at 07:59

0

If you use Maven, you must to declare your source and test folder in project directory.

For these, click F4 on Intellij Idea and Open Project Structure. Select your project name on the left panel and Mark As your "Source" and "Test" directory.

answered Aug 27 '19 at 07:59

Uğur Abdioğlu

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score 0 · Answer 13 · answered Apr 26 '23 at 02:53

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Go to file- Project Structure - Project and in sdk select your Java jdk file

answered Apr 26 '23 at 02:53

Kritika Gupta sp1 Kritika Gupt

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Unable to run Java code with IntelliJ IDEA

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