Error: Could Not Find Or Load Main Class

Java is generally used for sophisticated coding that ranges from mobile applications to web applications and web services. There really is a never-ending use of Java in this era of technological advancements.

Java offers certain benefits that have most developers referring to Java for their coding needs. A major benefit of using Java is that it is independent of any other platform.

This means that it can run on any system and does not require any specific hardware or software.

It is fast and provides a secure option when it comes to programming languages. If you have been studying up on developing for a while now you might be familiar with the phrase “Compile once and run forever.”

What Is Compiling?

Wondering what that means?

Well for those of you who haven’t heard of it, let me elaborate.

Once you have generated a Byte Code you can switch it over to any device and it will be able to convert into the machine code and run it perfectly without you having to do anything. So compile a code once and run it forever! Simple as that. Right?

As fun and easy as it sounds, compiling is a hellhole in and of itself. So if you find yourself crying in the middle of coding because you are having trouble in compiling the program, don’t panic!

Compiling Errors

This guide is specifically written to help you identify basic issues and their solutions. To read about why ‘not panicking’ is such a great idea, check out this mostly unrelated article where I refer to the troubleshooting process in more detail.

Troubles compiling and running Java code can spring from a diverse set of reasons. This commonly occurs when you try to run your Java program using a Java command line that has a given main class. So what is actually happening here you might wonder? Putting it as simply as possible, Java is not able to find the piece of code associated with what it’s trying to do.

In Java, a programmer will try to create classes that contain all sorts of things like objects, methods or functions, and through all that, net you the end result of doing ‘something’ with that class. In your specific scenario, Java couldn’t find the class it’s looking for – but maybe with the help of the droids we’re looking for, we can find a solution!

If you’re a beginner, it’s crucial for you to have an understanding of a few things beforehand. Learning about Java classes can be complex- and trust me, at one point you might feel like losing it, but do not give up hope yet! This guide will help you resolve the issues you’ve been having, and on the off chance it doesn’t, you’ll at least learn something you didn’t know. Win-win!

Stumbled onto our very useful site but have other sorts of woes in error codes? Check out this Ultimate PS4 Error Code List, or this very common Error Retrieving Information from Server Google Play Error explained!

So, First Thing’s First: What’s A Classpath?

A classpath is a parameter that a Java compiler uses to specify a user-defined location.

This location is set by a command-line, or you can use an environment variable, which is a story for another day and time. For now, remember that the directory of classpath is used by ClassLoaders. The purpose is simple, to find and load a class.

As much as learning about the concept of Classpath is included in Java, it is equally complex and overlooked by many aspiring developers.

Honestly, if you don’t give enough significance to learning Classpath, then buckle up for a ride full of difficulties. It’s a harsh truth, but it’s better to face it than end up hating programming just because you could not understand it properly. In fact, when you’re done learning the basics, the second thing you should learn is Classpaths in Java.

“What’s kept Java from being used as widely as possible is there hasn’t been an Open Source implementation of it that’s gotten really widespread use.” – Brian Behlendorf

Does This Ring Any Bells?

So you tried your hand at coding something…and it didn’t work. What’s up with that?  Sometimes, those who are self-taught end up missing out on the little things that are supposed to be learned in the very beginning. This might be the source of your current issue at hand as well- in which case my job becomes a lot easier. Does the code below look familiar to you?

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;

 

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   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));

   }

 

}

 

YES! This is exactly the one I tried. If you catch yourself thinking that then you might as well commend my analysis skills. Moving on, here is one area where you went wrong. After running this code you might see the following error being displayed: “Could not find or load main class.”

This error code is a simple one to figure out since the solution is named in the error itself:

  • Java is unable to locate the main class file. To solve this, make sure that you add a location of your .class file to the specified classpath.
  • To do this, you need to use your IDE’s preferences.
  • So if you’re using Eclipse try: Project -> Properties -> Java Build Path -> Add Class Folder.

Pro Tip: There are two different types of Classpath separators. For Windows it is a semicolon “;” and for Linux, it is a colon “:” There are many other key differences in windows and Linux codes. If you are eager to learn more about the differences among Windows and Linux Java codes, here is an article that will help you out.  

 What to Do When Class Is In a Package

When calling the following command you may end up having to deal with the error yet again:

java -classpath . TheClassName

To solve this issue, try a fully-qualified name, such as:

java -classpath . thepackagename.TheClassName

Remember that this command should be called from the same directory where thepackagename directory exists. This is really easy to miss but very crucial.

Working With Eclipse?

What’s Eclipse, you ask? It’s an open source platform that allows you to potentially develop your new Java application, applet or another form of code using an IDE that is common and familiar among most developers.

Make A Cleanup

There are many things that prevent Java to compile properly and this is one of them. A simple cleanup helps:

project\clean.. clean all projects

Want a clean up every time you save? Refer to the method in this link to format and clean up code every time you save in Eclipse.

Wondering a way to run your Windows machine in a ‘clean mode?’ Refer to the brief directions I give here about what to google about ‘Clean Boot!’

Are PATH and CLASSPATH The Same Thing?

My answer to that is a no. As confusing as the terminologies might be there is still quite a lot of difference among them.

PATH is used to locate commands in Java whereas on the other hand CLASSPATH is used to locate Java class files. Classpath is said to be an environment variable, which is used by Java Virtual Machine. Below is a picture attached to the Java build path.



How Do I Override Classpath in Java?

Confused about how overriding in Java works? Sometimes the solution to a problem is right under your nose and maybe that is why you can’t point it out.

You can do the overriding of Classpath in Java using –cp or –classpath. Do so while you are running the Java program.

This is one of the best ways to have different Java applications running simultaneously on the same machine. There is a general way to define a Classpath for Java applications, which you can do by creating a startup for Java program, and set Classpath there. You can do this via:

CLASSPATH=/home/tester/classes
java -cp $CLASSPATH Test

Java Classpath will point to the current directory by default that is denoted by “.” Yet it will look for any other class given that it is only in the current directory.

Conclusion

All in all, Java can be a valuable language in this era and is mastered perfectly, even so, the road to mastering Java might be a really rocky one. Once you are past the learning phase you will be surprised at what implementations Java provides on multiple platforms. Are you thinking about taking the whole programming thing seriously and looking for Free Java Software? Download from here now.   

Wondering maybe what all those HTTP error codes mean while you browse the web? Try this article here on Error Codes Pro I wrote about the Ultimate HTTP Error Code List!

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