Could not find the main class error when running jar exported by Eclipse

Question

I have a java project that works perfectly fine when running it from within Eclipse  When I try to export it to either a  JAR file  or  Runnable JAR file  the  jar file is created  but when I double click on it to try to run the program it gives me an error that says    Could not find the main class  package MainClassName  Program will exit     As I mentioned  I tried exporting to both JAR options  I specified the correct class that the main method is in  and when I look through the actual files in the  jar file everything seems to be in order -- the manifest looks something like   Manifest-Version  1 0 Main-Class  package MainClassName  blank line    and is in the META-INF folder  There is a folder with my package name  which contains all the  class files  including the class that contains the main method  A few image and text files that I use also appear in the jar file   The actual program isn t anything too complicated -- it s a simple  snake  game using Swing  plus the code all works when run from inside Eclipse    Any ideas what is causing this error and how I can fix it  Let me know if there s any other information I should provide

User · Answer

Verify that you can start your application like that:

java -cp myjarfile.jar snake.Controller

I just read when I double click on it - this sounds like a configuration issue with your operating system. You're double-clicking the file on a windows explorer window? Try to run it from a console/terminal with the command

java -jar myjarfile.jar

Further Reading

Running JAR file on Windows

The manifest has to end with a new line. Please check your file, a missing new line will cause trouble.

User · Answer

Have you renamed your project main class  e g  through refactoring    If yes your Launch Configuration might be set up incorrectly  e g  refering to the old main class or configuration   Even though the project name appears in the  export runnable jar  dialog  a closer inspection might reveal an unmatched main class name   Go to  Properties- Run Debug Settings  of your project and make sure your Launch Configuration  the same used to export runnable jar  is set to the right name of project AND your main class is set to name space of your project YouMainClass

User · Answer

For netbeans user that having this problem is as simply   1 Go to your Project and Right Click and Select Properties  2 Click Run and also click browser   3 Select your frames you want to first appear

User · Answer

I ran into the same issues the other day and it took me days to make it work  The error message was  Could not find the main class   but I can run the executable jar exported from Eclipse in other Windows machines without any problem   The solution was to install both x64 and x86 version of the same version of JRE  The path environment variable was pointed to the x64 version  No idea why  but it worked for me

User · Answer

Right click on the project  Go to properties  Click on Run Debug Settings  Now delete the run config of your main class that you are trying to run  Now  when you hit run again  things would work just fine

User · Answer

Ok  so I finally got it to work  If I use the JRE 6 instead of 7 everything works great  No idea why  but it works

User · Answer

Run it like this on the command line   java -jar  path to your jar jarFile jar

User · Answer

Had you tried creating a  jar file manually instead of using Eclipse  Try the following steps  hopefully that might help    Considering that your directory structure looks like this      TicTacToe Your Project Name I mean                                       src            bin             manifest txt                                icons  tictactoe   Now suppose that my main class is BeginGame inside package tictactoe  so I will write inside my manifest txt file this thing     Main-Class  tictactoe BeginGame   Do remember the space between colons   and package name i e  tictactoe  and immediately after BeginGame press Enter and save the file   Now on your command prompt go to the location of bin folder  I am describing my side as follows     C  Mine Eclipse TicTacToe bin gt jar -cfm    tictactoe jar    manifest txt tictactoe icons    Here the first argument i e     tictactoe jar is used to tell that create tictactoe jar one level up  i e  inside TicTacToe Folder  Second argument    manifest txt means that the manifest txt file is located one level up  i e  inside TicTacToe Folder  Third and Fourth arguments tictactoe and icons means  that add both these folders to the  jar file  since they are placed inside bin Folder so they are used as it is  Now Press Enter    Now try to run your  jar file so created inside the Project Folder  TicTacToe Folder  in my case     Hopefully this will work

[java] "Could not find the main class" error when running jar exported by Eclipse

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