Error Could not find or load main class in intelliJ IDE

Question

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

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I have tried all the hacks suggested here - to no avail  At the end I have simply created a new Maven application and manually copied into it - one by one - the pom xml and the java files and resources  It all works now  I am new to IntelliJ and totally unimpressed but how easy it is to get it into an unstable state

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This might help   1   Build  menu -   Rebuild Project   Sometimes Intellij doesn t rewrite the classes because they already exist  this way you ask Intellij to rewrite everything   2   Run  menu -   Edit configuration  -  delete the profile -  add back the profile   Application  if it s a Java application   choose your main class from the  Main Class  dropdown menu    3  Build  menu -   Rebuild Project

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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

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For me - i tried few of the options above  did not work  Then i just renamed my Application class and that probably forced intelliJ to build a fresh jar and error message started to change  Then i renamed it back and it worked

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Explicitly creating an out folder and then setting the output path to C  Users USERNAME IdeaProjects PROJECTNAME out    seemed to work for me when just out  and expecting IntelliJ to make the folder wouldn t     Also try having IntelliJ make you a new run configuration   Find the previous one by clicking    then remove it    and hit okay   Now   IMPORTANT STEP  open the class containing your main method  This is probably easiest done by clicking on the class name in the left-hand side Project Pane   Give  er a Alt   Shift   F10 and you should get a    Now hit Enter    Tadah    Did it work

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Follow these steps   Go to run Go to edit configurations Click the green colored   sign in top left corner Select the type you are working  for instance  Applications  Now enter the name of the class which you want to run instead of unnamed  Do the same where it is written Main class just below it    Yippee    your code will run

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Invalidate cache and restart your IntelliJ  it worked for me

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For me the solution was to fix the output directory under project settings   Before I was using just  target  for the Project compiler output   Instead I updated it to have a full path e g  D  dev sigplusjava2 68 target

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modules xml with wrong content  I don t know what s matter  with my IDEA

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I got this error when using Scala SBT  IntelliJ could not find the main class  even though everything was set up correctly  My solution  delete the  lt user gt   sbt  lt version gt  plugins target folder  then restart IntelliJ

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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

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Simple solution is go to the backed folder in command line  where the root folder of the project  You should  have SBT installed in your machine     If you have sbt installed  please run the command  sbt package   this will recompile the project if it success  come back to the intelliJ it will work

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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

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In my case  I had  relatively  long vm arguments configured  Converting these arguments  whenever possible  to environment variables fixed the issue for me

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In my case  the application runs well when code initially was under  src directory under the project  Later I added  main java directory after the  src  then  Could not find or load main class      error happened  At that time you couldn t add  src main java YourMain java to the run configuration  What I did was to remove the run configuration  then right click the project- Open Module Settings  or F4 after click the Project panel - Project Settings- Modules delete  x  the old Content Root and   Add Content Root  choose  src main java  Rebuild the project and it runs

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In my case in the module s build gradle the mainClassName assignment must state the fully qualified class name  ie   as specified as the package name in the main class  source code file

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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

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I have faced such problems when the class is in the default folder  i e  when the class does not declare a package   So I guess using a package statement  eg  package org me mypackage   on top of the class should fix it

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You probably would have specified a wrong package and the package hierarchy would not be right  Look below    The ide would highlight the wrong path in that case

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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

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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 must work now

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Just re-build the project  CTRL F9  and double check  Edit Configurations  if you have a properly set Main class  and module  if any

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Check your class module   I have encountered this problem with intellij   I have a maven multi-module project  the problem is that i runing a class which not exist the  module within the configuration  so my problem is fixed by setting the right module   edit configuration  -   use class of module     may this help you

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I inherited a bunch of  JAVA files from elsewhere and couldn t figure out how to get them to work in any IDE  Ultimately I had to go to the command line where the Main JAVA file was and run javac Main java   This created a bunch of  CLASS files   The IDE s were then able to figure out what to do

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File  gt  Project Structure  gt  Modules  gt  Mark  quot src quot  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

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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

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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- gt Manage IDE Settings- gt 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

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Mark the directory as a source directory  Opened via Ctrl Shift Alt S

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I had this problem and I tried everything under the sun that I could think of and on this site    None of my Java classes were being picked up after I pulled from a remote branch  All the classes had red Js by their names in the Project Hierarchy  not blue Cs   In the end  I tried to follow this tutorial and a few steps in tried something not described and fixed the issue  https   www jetbrains com help idea creating-and-managing-modules html  Here s what I did    Goto File   Project Structure  or press Crtl Shift Alt S Select Modules under the Project Settings section   In the Sources tab click Sources on the  Mark as   line   Click the Apply button     For some reason  all my classes then had blue C s    Someone with a better understanding of how IntelliJ and or IDE s might be able to explain the phenomenon  but all I know is now it can see all the classes and more importantly the main one  and run

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I had to mark the  src  folder as  Sources   After restarting IntelliJ and rebuilding the project I could run the project without further issues  see screenshot   Edit  You can access the  Project Structure  tab via File- Project Structure or by pressing Ctrl Shift Alt S

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Try to check your project name and full directory name  see if contain any  un-English  words like Asian words   sometimes this could be the fault  Rename the project name or project path contains such words and reopen it might work

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Elaborating on Brad Turek s solution    One of the default IntelliJ Java project templates expects a file called Main defining the class Main and main   method entry point  If the method is contained in another file  and class   change the Run configuration   Run Configuration Window   With the project open in IntelliJ  use the Run Edit Configurations    menu to open the build configuration window   If the entry for Main class doesn t list the name of your file containing the class exposing the main   entry method  enter the correct file name   The configuration in the image is wrong  which is why it s red in the configuration panel    My main   entry method is in the class  and file  ScrabbleTest  So changing Main class  to ScrabbleTest fixes the runtime error    As others have noted you have to ReBuild using the new configuration  I am using a package  but that doesn t seem to make a difference IME  Hope this helps

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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

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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  quot arg with space must be quoted quot

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I meet same problem and solved it by   Closing all IDEA windows Delete C  Userz xx  IdeaIC2019 3 folder Reopen IDEA

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I know this was asked a while ago  but I was just stumbling over this issue and thought my findings might help others  As pointed out  the error message is basically a result of the out folder  That s because  when you re trying to run the program  it compiles the code first  and puts the compiled result to the out location  and then it tries to load the compiled code from the out location  If the compiled code is not in the location expected  you ll get the error    The point I m particularly wanting to share is that some times  the code is not compiled  built   even though your run configuration specifies  Build  in the  Before launch  section of the configuration panel    When can this happen   One situation that can cause this to happen is if you re using modules and you manually delete the module out directory  For example  if I have a module named  foo   there should be a directory named foo under out production  If you manually delete it  the build system may not know that it needs to be rebuilt    Even worse  if you select Build   Build module  foo   it still may not rebuild the module  If that s the case  you should select a file in the module  for example  bar java  and then select Build   Recompile  bar java   Now the out directory out production foo should be restored    Since IntelliJ typically knows about any changes going on  this surprised me  and took me a little time to figure out  so I thought I d share

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In my case  it is a maven project  I Reimported maven  right click on pom xml file and click Reimport  that s it worked immediately

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In my case the problem seemed to be related to upgrading IntelliJ  When I did this I overwrote the files from the old IntelliJ with the files from the new IntelliJ  2017 community to 2018 community   After that all of my projects were broken  I tried everything in this thread and none of them worked  I tried upgrading gradle to the latest version  4 to 4 8  and that didn t work  The only thing that worked for me was deleting the entire IntelliJ folder and reinstalling it  All of my projects worked after that

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

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