Error: Could not find or load main class [duplicat

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• What does “Could not find or load main class” mean? 41 answers

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 < VENSIM_CONTEXT_CREATION_MAX_FAILURE_COUNT && 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 > 0 && args[0].equals("info")) {
            System.out.println(new VensimHelper(libName, modelPath).getVensimInfo());
        } else if (args.length > 0 && 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));
    }

}

Answer 1

If you try to run a java application which needs JDK 1.6 and you are trying to run on JDK 1.4 then you will come across this error. In general trying to run java appliation on old JRE may fail. Try installing new JRE/JDK

Answer 2

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.

Answer 3

check your BuildPath, it could be that you are referencing a Library which is not anymore existing.

Answer 4

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).

Answer 5

You must ensure that you add the location of your .class file to your classpath. So, if its in the current folder then add . to your classpath. Note that the windows classpath separator is a semi-colon ie ;

Answer 6

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.