Eclipse can t find load main class

Question

My Eclipse  Indigo  was running just fine   I created a simple class Hello   It is placed in package cont in the folder ch13   However  when I try to run it from Eclipse I get info from Java Virtual Machine Launcher    Could not find the main class  cont Hello      I tried to run other classes from this package and they run just fine  that is the classes that existed there before    However any new class I create in this package has these problems   Actually any new class I create in Eclipse runs into this problems   I decided to check how it works from the command line   It seems that the problem still exist - I get same error   I checked the path and it is C  Program Files Java jdk1 7 0 02 bin  which is correct  note the other classes are running from Eclipse just fine    I tried to run with java -cp   Hello and there are some Errors produced starting with java lang NoClassDefFoundError  Hello  wrong name  cont Hello    Code itself is simple   package cont   public class Hello       public static void main String   args           System out println  Hello               How can I fix it so that my classes still run under Eclipse

User · Answer

You must have main function in your class  Like public class MyDataBase        public static void main String args

User · Answer

I had this same problem in a Maven project  After creating the src test java folder within the project the error went away

User · Answer

Move your file into a subdirectory called cont

User · Answer

I had the same problem  this is my solution    I manually deleted the bin folder of the project Then I refreshed the project which recompiled the whole project and created a new bin with all  class files   I did it because when I performed Clean project- clean  my  class files were not getting deleted  the above solution works for me hope its useful to others

User · Answer

metadata is corrupted   Steps   Warning  Deleting  metadata will delete all your Eclipse configurations  plugins  project setups  Make a backup before you attempt this    Stop eclipse  delete  metadata in workspace and restart eclipse Import Project Run again

User · Answer

I solved this error by closing the project  removing it from eclipse and then importing it again    Might be a little simpler than to redo the whole workspace setup

User · Answer

I solved my issue by doing this    cut the entire main  CTRL X  out of the class  just for a few seconds   save the class file  CTRL S  paste the main back exactly at the same place  CTRL V    Strangely it started working again after that

User · Answer

This worked for me finally    RUN -  RUN CONFIGURATIONS -  DELETE THE RUN CONFIGURATION CLOSE ECLIPSE REOPEN ECLIPSE CREATE RUN CONFIGURATION AGAIN   Tadaaaa    It works

User · Answer

I read so many blogs and tried so many tricks but my problem not resolved  I was able to run the code but not able to generate the jar file     Sad   But I tried something which might be very silly but worked for me and bought eclipse on trace  What I did was   Just deleted the main method from the class  Saved it  Did undo to bring the main class back  Tada    Issue resolved    Just one think would like to say  keep your eclipse in  quot Build Autometically quot  mode

User · Answer

Renaming the main class should be enough  and easiest   - Go to your class and set cursor to your class name  - ALT   Shift   R and rename the class  build if not done automatically   - You should be able to run it now  - Rename the class to the old name if you want

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Note  This worked in the past and I received many up votes  Perhaps this is not a solution anymore - but it once was - as the eclipse version was indicated   Problem This can also be caused by a Java Build Path Problem  In my case  I had a an error  A cycle was detected in the build path of project  project   The cycle consists of projects  x  y  z   This can occur when you include other projects in the build path of the project you wish to run  In fact  all the projects will fail to run with the error Could not find the main class  Example class  Solution Open Windows - gt  Preferences - gt  Java- gt  Compiler - gt  Building - gt  Build Path Problems Uncheck the Abort build when build path errors occur toggle This seems like a can of worms if you end up with other build path errors I image  So use with caution    Note  This only works if you have a  quot cycle error quot   This error message can be found in the  quot Markers quot  tab  I found the solution to this here  Info  Java 1 8 0 152 Eclipse Photon  June 2018

User · Answer

Another tip  I initialized static fields in a wrong order - surprisingly it didn t bring up a Problem  NullPointerException    instead Eclipse complained with exactly the message OP posted  Correcting the static initialization order made the class run-able  Example   private static ScriptEngineManager factory   null  private static ScriptEngine engine   null  static       engine   factory getEngineByName  JavaScript           factory is supposed to initialize FIRST     factory   new ScriptEngineManager

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I had this issue after upgrading to the Eclipse 2019-12 release  Somehow the command line to launch the JVM got too long and I had to enable the jar-classpath option in the run configuration  right click on file -  run as -  run configs

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Standard troubleshooting steps for Eclipse should include deleting and re-importing the project at some point  which when I have dealt with this error has worked

User · Answer

I found the way to fix this problem was to rename the project  If you give it a name with strange characters  in my case      it will have trouble locating your class  I don t know if this rule applies to numbers  but try renaming the project or making a new one and copying the files  Name it without any numbers or special characters

User · Answer

If you are using a pre-defined run configuration  go to classpath and try  Restore Default Entries   This will reconfigure the classpath for that configuration

User · Answer

Removing the Run Configuration  Sometimes I have a similar problems in some pre-release versions of eclipse  For fix the error  I delete the Run Configuration  You can find that in menu Run  Run Configurations     Then I launch the app with Alt Shift X  then J  If this don t work  Ctrl F11  Deleting the  metadata directory  In another way  the configuration settings for your current workspace may are corrupted  Those settings are in the  metadata directory in your current workspace 1  In that case  there is no other choice than delete the directory    Close eclipse   Delete the  metadata directory  Start eclipse  Import the projects  Run the project again        Notes   You will see that directory with File   Switch Workspace   Other

User · Answer

I have solved the issue following way   Go to Run Configuration  Right Click on Java File- Run- Run Configuration    Go to ClassPath Tab  Click on Advanced -  Add Folders -  Add bin directory  which has class file in it for Java source code   Re run the code  now it will solve the issue  It worked for me

User · Answer

I had the same problem I solved  with following command maven   mvn eclipse eclipse -Dwtpversion 2 0  PS  My project is WTP plugin

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It is possible to have 2 groovy-xxx-all jar files by excample in lib directory  which makes that an app is not running

[java] Eclipse can't find / load main class

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