Error Could not find or load main class

Question

I am having trouble compiling and running my Java code  intended to allow me to interface Java with a shared object for Vensim  a simulation modeling package   The following code compiles without error   javac -d   -cp   apache-log4j-1 2 16 log4j-1 2 16 jar   vensim jar SpatialModel java     VensimHelper java VensimException java VensimContextRepository java   However  when I try to run the following   java -cp   apache-log4j-1 2 16 log4j-1 2 16 jar   vensim jar SpatialModel vars   I get the following error   Error  Could not find or load main class SpatialModel     My SpatialModel java code does contain a  main  method  below   so I m not sure what the problem is - can anyone please help me out   Thanks   import java io File  import java text NumberFormat  import java util ArrayList  import java util Arrays  import java util List   import org apache log4j Logger   public class SpatialModel        private VensimHelper vh       public static final String DLL LIBNAME PARAM    vensim lib nam        public static final String MODEL PATH PARAM    vensim model path        private final static int VENSIM CONTEXT CREATION MAX FAILURE COUNT   10       public SpatialModel   throws SpatialException            String libName   System getProperty DLL LIBNAME PARAM           String modelPath   System getProperty MODEL PATH PARAM                    if libName    null    libName trim   equals                    log error  Vensim library name has to be set with -D    DLL LIBNAME PARAM               throw new SpatialException  Vensim library name has to be set with -D    DLL LIBNAME PARAM                      if modelPath    null    modelPath trim   equals                    log error  Model path has to set with -D    MODEL PATH PARAM               throw new SpatialException  Model path ahs to be set with -D    MODEL PATH PARAM                      for  int i   0  i  lt  VENSIM CONTEXT CREATION MAX FAILURE COUNT  amp  amp  vh    null  i                  try                   log info  creating new vensim helper n tdll lib      libName     n tmodel path      modelPath                   vh   new VensimHelper libName  modelPath                 catch  Throwable e                    log error  An exception was thrown when initializing Vensim  try      i  e                                   if  vh    null                throw new SpatialException  Can t initialize Vensim                          public static void main String   args  throws VensimException            long before   System currentTimeMillis               String libName   System getProperty DLL LIBNAME PARAM           String modelPath   System getProperty MODEL PATH PARAM            if  libName    null                libName    libvensim                     if modelPath    null                modelPath      BassModel vmf                      System setProperty DLL LIBNAME PARAM  libName           System setProperty MODEL PATH PARAM  modelPath            if  args length  gt  0  amp  amp  args 0  equals  info                  System out println new VensimHelper libName  modelPath  getVensimInfo               else if  args length  gt  0  amp  amp  args 0  equals  vars                  VensimHelper helper   new VensimHelper libName  modelPath               String   vars   helper getVariables                for  String var   vars                    System out println helper getVariableInfo var                            else                File f   new File                   System out println f getAbsolutePath                  SpatialModel sm   new SpatialModel                       System out println  Execution time       System currentTimeMillis   - before

User · Answer

I have a similar problem in Windows  it s related to the classpath  From the command line  navigate until the directory where it s located your Java file    java and   class   then try again with your commands

User · Answer

Project   Clean and then make sure BuildPath   Libraries has the correct Library

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This problem occurred for me when I imported an existing project into eclipse  What happens is it copied all the files not in the package  but outside the package  Hence  when I tried run   run configurations  it couldn t find the main method because it was not in the package  All I did was copy the files into the package and Eclipse was then able to detect the main method  So ultimately make sure that Eclipse can find your main method  by making sure that your java files are in the right package

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I got this error because I was trying to run  javac HelloWorld java  amp  amp  java HelloWorld class   when I should have removed  class   javac HelloWorld java  amp  amp  java HelloWorld

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java -verbose class HelloWorld might help you understand which classes are being loaded   Also  as mentioned before  remember to call the full qualified name  i e  include package

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If you work in Eclipse  just make a cleanup  project clean   clean all projects  of the project

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If you try to run a java application which needs JDK 1 6 and you are trying to run on JDK 1 4  you will come across this error  In general  trying to run a Java application on old JRE may fail  Try installing new JRE JDK

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If the class is in a package  package thepackagename   public class TheClassName     public static final void main String   cmd lineParams          System out println  Hello World              Then calling    java -classpath   TheClassName   results in Error  Could not find or load main class TheClassName  This is because it must be called with its fully-qualified name   java -classpath   thepackagename TheClassName   And this thepackagename directory must exist in the classpath  In this example     meaning the current directory  is the entirety of classpath  Therefore this particular example must be called from the directory in which thepackagename exists    To be clear  the name of this class is not TheClassName  It s thepackagename TheClassName  Attempting to execute TheClassName does not work  because no class having that name exists  Not on the current classpath anyway   Finally  note that the compiled   class  version is executed  not the source code   java  version  Hence    CLASSPATH

User · Answer

Problem is not about your main function  Check out for  javac -d   -cp   apache-log4j-1 2 16 log4j-1 2 16 jar   vensim jar SpatialModel java     VensimHelper java VensimException java VensimContextRepository java   output and run it

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I use Anypoint Studio  an Eclipse based IDE   In my case everything worked well  until I found out that while running the java code  something totally different is executed  Then I have deleted the  class files  After this point I got the error message from this question s title  Cleaning the project didn t solve the problem   After restarting the IDE everything worked well again

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You can try these two when you are getting the error   could not find or load main class   If your class file is saved in following directory with HelloWorld program name d  sample   java -cp d  sample HelloWorld java -cp   HelloWorld

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If you re getting this error and you are using Maven to build your Jars  then there is a good chance that you simply do not have your Java classes in src main java    In my case I created my project in Eclipse which defaults to src  rather than src main java    So I ended up with something like mypackage morepackage myclass and a directory structure looking like src mypackage morepackage myclass  which inherently has nothing wrong  But when you run mvn clean install it will look for src main java mypackage morepackage myclass  It will not find the class but it won t error either  So it will successfully build and you when you run your outputted Jar the result is   Error  Could not find or load main class mypackage morepackage myclass   Because it simply never included your class in the packaged Jar

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You have to include classpath to your javac and java commands  javac -cp   PackageName   java java -cp   PackageName ClassName Having main   suppose you have the following   Package Named  com test Class Name  Hello  Having main  file is located inside  src com test Hello java   from outside directory      cd src   javac -cp   com test   java   java -cp   com test Hello    In windows the same thing will be working too  I already tried

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You have to set the classpath if you get the error       Could not find or load main class XYZ   For example   E   gt set path  c  programfiles Java jdk1 7 0 17 bin  E   gt set classpath  classpath     E   gt javac XYZ java E   gt java XYZ

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You must ensure that you add the location of your  class file to your classpath  So  if its in the current folder  add   to your classpath  Note that the Windows classpath separator is a semi-colon  i e  a

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This solved the issue for me today   cd  path to project cd build rm -r classes   Then clean amp build it and run the individual files you need

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If you are using Eclipse    I renamed my main class file and got that error   I went to  Run As  configurator and under the class path for that project  it had listed both files in the class path   I removed old class that I renamed and left the class that had the new name and it compiled and ran just fine

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I was using Java 1 8  and this error suddenly occurred when I pressed  Build and clean  in NetBeans  I switched for a brief moment to 1 7 again  clicked OK  re-opened properties and switched back to 1 8  and everything worked perfectly   I hope I can help someone out with this  as these errors can be quite time-consuming

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I believe you need to add the current directory to the Java classpath  java -cp     apache-log4j-1 2 16 log4j-1 2 16 jar   vensim jar SpatialModel vars

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If so simple than many people think  me included     cd to Project Folder src package there you should see yourClass java then run javac yourClass java which will create yourClass class then cd out of the src folder and into the build folder there you can run java package youClass  I am using the Terminal on Mac or you can accomplish the same task using Command Prompt on windows

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Check your BuildPath  it could be that you are referencing a library that does not exist anymore

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I know this question was tagged with linux  but on windows  you might need to separate your cp args with a   instead of a     java -cp   apache-log4j-1 2 16 log4j-1 2 16 jar   vensim jar SpatialModel vars  http   docs oracle com javase 7 docs technotes tools windows classpath html

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

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