Friday, 5 August 2016

java - Error: Could not find or load main class




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



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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