Reputation: 2739

Error: Could not find or load main class in intelliJ IDE

I'm a beginner in Java and am trying to run my code using IntelliJ that I just installed as my IDE with JDK 1.7. The following piece of code keeps does not even compile and keeps giving me the error:

Error: Could not find or load main class libTest

Code

import java.lang.Integer;
import java.lang.String;
import java.lang.System;
import java.util.*;

class book {

    private String name = "trial";
    private int bookCode=1;
    private int issued=0;

     public void Issue(){
         if(issued==0) {
             issued=1;
             System.out.println("You have succesfully issued the book");
         }
         else {
             System.out.println("The book is already issued. Please contact the librarian for further details");
         }
    }

    public int checkCode() {
        return bookCode;
    }

    String readName() {
        return name;
    }

    public void setName(String newName){
        name=newName;
    }

    public void setBookCode(int newCode){
        bookCode=newCode;
    }
}

class library {
    private ArrayList books=new ArrayList();

    public void getList(){
        for(int bk:books){
            String bName=books(bk).readName();
            System.out.println((bk+1)+")  "+bName);
        }
    }
}

public class libTest{
    public static void main(String[] args){
        library newLib= new library();
        System.out.println("code working");
   }
}

Is there any change that i have to make in the compiler settings?? Or is it the code.

Upvotes: 263

Answers (30)

Sai Pe Pu

Reputation: 11

In my case, I name the file as "First Last" with space between. The project can be run after refactoring the name.

Upvotes: 0

HHH

Reputation: 310

For me , just Reload Project from pom.xml

Upvotes: 0

SUPARNA SOMAN

Reputation: 2693

This worked for me:

Right-click the folder where your class is in >> down you'll see an option "Mark Directory As..." Then you mark it as Source root.

Upvotes: 1

Michael Mesfin

Reputation: 556

remove any README.md files or files with .md extensions from your project

Upvotes: 0

Susobhan Das

Reputation: 1174

No-brainer straightforward answer for Windows

Delete the C:\Users\username\AppData\Local\JetBrains\IdeaIC2023.3 folder. The folder is present inside AppData folder, which can be navigated from C:\ and then Users, current user and there you can see the AppData folder.

Close all IDEA windows
Delete C:\Users\username\AppData\Local\JetBrains\IdeaIC2023.3
Reopen IDEA

After deleting the IdeaIC2023.3 folder, and re-opening IntelliJ it starts to re-structure the project, and the error gone.

Upvotes: 0

youhans

Reputation: 6869

If none of the above answers worked for you, just close your IntelliJ IDE and remove the IntelliJ IDE file and folder from the root of your project:

rm -rf .idea *.iml

Then, open the project with IntelliJ. It should work now.

Upvotes: 280

svassr

Reputation: 5668

Go in Run/Debug Configuration panel.
Below "Build and Run" make sur the given mainClass name is correct and edit it if necessary.

Upvotes: 0

Rawand Saeed

Reputation: 855

Delete .build folder and restart IntellJ IDE.

Upvotes: 0

Alphons

Reputation: 323

After trying out almost every suggestion in this tread I was still out off luck. Tried them on two different machines. Consulted an experienced colleague.

And finally: A solution to my problem, and probably the cause of the isssue:

One of the folder names contained a forward slash on my Macs that's it

(We used a (deeply) nested folder structure on a shared drive; and my colleague works on Windows and doesn't have an issue with the forward slash in the path)

NOTE: while I wanted to supply my answer here on stackoverflow in this thread, I got a 'warning' from stackoverflow that there where already more than 30 answers. But he, to no avail for me. And because it's a thread that dates from 2012 and is still active in 2023 with so many answers (and cause's of the same problem). I decided to add my fifty cents here as well. Hope it helps and saves somebody's time!!

Upvotes: 0

parsa

Reputation: 995

You can run the maven command on the pom.xml file in your project directory:

mvn clean install

Upvotes: 4

Prajwal S M

Reputation: 203

for me deleting .idea file in your project directory worked fine! close the ide , delete the .idea in your project , open the project build and load !

Upvotes: 2

Marco

Reputation: 444

Tried everything, no luck. Finally, the simple solution that worked for me (on a Mac) was:

while the project is open, go to the finder and move the src directory out of the project folder. IntelliJ realizes that the src is not there any more, and updates itself.
with the project still open, move the src directory back in place. IntelliJ updates its project configuration, and at this point everything works.

Upvotes: 1

Harsha

Reputation: 1756

I got the issue when I went to "Edit configurations" -> "Modify options" and checked the "Do not build before run" option, as I use IntelliJ for short programming problems and I don't want it to run the build every time.

What I instead did is to assign a shortcut that runs the build process (only for the first time after a class is created), which fixes the error and then another convenient shortcut to "Run context configuration" that successfully runs the main method in whichever class is currently in focus.

Upvotes: 0

Shyam

Reputation: 127

Goto File-> Invalidate Caches and Restart . Else delete rm -rf .idea *.iml and restart InteliJ

Upvotes: 2

Vijay

Reputation: 313

choose maven as the type while creating project (do not check create from archetype checkbox)
Inside Project explorer, right click on java under main under src
choose new class
complete the class with public static void main
choose run from run menu

Upvotes: 1

Smile

Reputation: 4088

Invalidating cache didn't work.

I edited the main class java file with a dummy change and ran it. It worked.

Upvotes: 3

CuriousIndeed

Reputation: 131

If you are using gradle try rebuilding the project by the command from the command line:

gradle clean build

Upvotes: 0

lleiou

Reputation: 495

After creating your project in intelliJ, try running the following command:

mvn package

Upvotes: 5

steven smith

Reputation: 1577

I am working with Kotlin but am guessing the problem is the same. I would start a project, create a single file and add main to it and the IDE couldn't find the main.

I tried the things in this list and none worked. I finally mentioned my frustration on one of the IntelliJ pages and was contacted. Of course, it worked fine for IntelliJ. After a couple of days back and forth, I noticed that the highlight function wasn't working and mentioned that. It turned out something was wrong with the IDE settings. I still don't know specifically what was wrong but the fix in my case was to reset the IDE settings. File->Manage IDE Settings->Restore Default settings.

After this, the green triangle start icon became visible to the left of my main function and things continued to work normally for subsequent projects.
Thanks to Konstantin at JetBrain's support for his patience.

Upvotes: 1

BovineScatologist

Reputation: 385

I have tried almost everything suggested in the answers here, but nothing worked for me.

After an hour of just trying to run my application, I noticed that my project's path included non-ASCII characters (Arabic characters). After I moved my project to a path with no non-ASCII characters, it executed just fine.

Upvotes: 3

S_K

Reputation: 829

Invalidate cache and restart your IntelliJ, it worked for me.

Upvotes: 43

Big Pumpkin

Reputation: 4497

I ran into this problem when my Java class was under src/main/kotlin. After I moved it to src/main/java, the problem was gone.

Upvotes: 7

ChrisZZ

Reputation: 2191

I meet same problem and solved it by:

Closing all IDEA windows
Delete C:/Userz/xx/.IdeaIC2019.3 folder
Reopen IDEA

Upvotes: 0

xXTurner

Reputation: 69

If the class which has the main method is extending/implementing another class/interface then it will not find the main class. Change the signature and it should work.

I had the same problem tried almost every answer from this thread non of them worked. Then this worked for me.

Upvotes: -1

Sumit Jadiya

Reputation: 767

File > Project Structure > Modules > Mark "src" folder as sources. This should fix the problem. Also check latest language is selected so that you don't have to change code or do any config changes.

Upvotes: 13

Yep

Reputation: 141

Another thing you can check here is the actual command that is being passed to the JVM and make sure it looks OK. Scroll to the top of your Run console, it should be the first line.

Spaces in your Run Configuration VM Options field will malform the app startup command and can result in this error message

-DsomeArgument="arg with space must be quoted"

Upvotes: 1

Tonecops

Reputation: 167

We are at File/Project Structure.. Answer might be:

Folder indicated as "content root" needs a child folder where the code is. Plus find the button that marks code as excluded and not. Not to be confused with tickbox that states excluded without telling in what phase and what** Is it compiler exclude or runtime exclude? You are doomed to test and lot. So no that tickbox but icons and colors.

As an idea we need to crack how it was originally thought to work. They never got it to work in first place and started add things in premature codaculation style. It has been so many years and you cannot expect any improvement. But as cure we can hack out some way to get it right every time.

Upvotes: 1

mark99

Reputation: 31

in my case it helped to remove the lines build.gradle

compile group: 'com.microsoft.sqlserver', name: 'mssql-jdbc', version: '8.2.0.jre11'

I don't know why this happens, but after adding the specified library, the compiled jar stops working

Upvotes: 0

Taras Melnyk

Reputation: 3275

Open Modules Tab (Press Ctrl+Shift+Alt+S). I had two modules under one project. I've solved the problem after removing the second redundant module (see screenshot).

Upvotes: 6

OHY

Reputation: 970

I'm using IntelliJ with Spring and my main class is wrapped in a JAR. I had to mark the 'Include dependencies with "Provided" scope' in the Run/Debug configuration dialog

Upvotes: 2

Error: Could not find or load main class in intelliJ IDE

Code

Answers (30)

Related Questions