Are you a Java developer and you suddenly encountered the “Could not find or load main class” error message out of the blue during compilation? Look, no further because everything you need such as the causes and how to fix this error message will be discussed here.
This annoying Java “Could not find or load main class” error occurs usually when the JVM fails to locate or load the main class while executing a program.
It happens most times when executing a Java program from the command line.
For more details on how to fix Java’s “could not find or load main class” error message, don’t skip a step until the end of this article.
What is Java Could Not Find or Load the Main Class?
In case you are wondering what could be the meaning of the Error message “Could not find a class or load the main class”, it simply means that the main class cannot be found or loaded even when a program is running.
In this post, you will learn the various reasons why this error keeps occurring and proven ways to rectify it.
What Causes the Java “Could not find or load main class” Error?
As stated earlier, the “Could not find or load main class” error occurs once the JVM fails to load the main class. However, the causes of this Jave error message can occur due to various reasons, such as the below:
- This error is caused once a program is executed in the terminal, and the main class is not found or can’t be loaded.
- This could also be caused primarily due to the programmer’s syntax errors.
- If the CLASSPATH environment variable where Java searches for all the class files doesn’t have the main class, then this error will be shown.
- Since Java is very case-sensitive, the wrong casing for the main class can cause issues.
- Note that if the class is inside a package, then the main class will not be loaded.
- The class may have been declared in the wrong package.
- The wrong directory may have been mentioned in the CLASSPATH.
- The file path of the class may not match the fully qualified name.
- The wrongly specified classpath of the application.
- The could not find or load the main class error could be caused by missing dependencies from the classpath.
- Wrong directory path on the classpath.
- A typographical error in the class name may be responsible.
These are the common causes of Java could not find or load the main class error.
Example of Could not find or load main class
Below is an example of the Java “Could not find or load main class” error displayed once a wrong class name is specified during execution:
- MyClass.java: Once the Java command is used to execute the .class file with a wrong name, the “Could not find or load main class” error will show. The generated .class file has the exact name of the Java class, which in this case is MyClass.class. Choosing the appropriate name will execute the program successfully.
How to fix Could not find or load main class Error
The “Could not find or load main class” error can occur in several ways while executing Java programs. Most times, it happens because of specifying a wrong class name, file path, classpath, or, class file extension.
The following steps below will help you to resolve the Java Could not find or load main class error message:
- Use the correct class name: Ensure you thoroughly check the spelling and casing of the class name while executing the program.
- Use the class name without the .class extension: The Java command expects the class name for accomplishing the program, without the .class extension. Therefore, the following syntax can be used to execute Java classes: java <classname>
- Use the correct file path: The path to the .class file must be checked and corrected in case an error occurs. Do not forget to use the fully qualified name of the class contained in a package if executing it from outside the directory structure of the package.
- You can use .back Command: In case the class exists inside a package, you can always go back to the main directory via the cd.. back command. For instance, the java class exists in the path below: E:\primary\com\projects. The full name of the class will be com.projects.Program1. Then use the cd.. back command to reach the parent directory primary, E:\primary. You can then run the java command to load the class via the following syntax: java com.projects.Program1.
- Use the correct classpath definition: The classpath should be thoroughly checked and defined correctly if an error comes up. It can as well be specified using the java -cp or -classpath command line arguments.
- Check Classpath directory and Sub-directory: You can as well check the directory and the sub-directory of the classpath. For instance, if the classpath is set to E:\primary\com\projects, then ensure that you don’t write E:\primary\projects\com.
How to Track, Analyze and Manage Errors with Rollbar
As we all know that managing errors and exceptions in your code can be quite challenging. Successfully tracking, analyzing, and managing errors in real-time can help you to go ahead with more confidence.
Rollbar assists to automate error monitoring and triaging, making fixing Java errors easier than ever. You can always try it out.
What causes this common Java error and some of the effective ways to prevent this error have been discussed in the article above. These fixes save Java developers a lot of time and stress when debugging, especially for complex codes!
Although basic syntax errors are the root causes of such issues, note that the casing of Java classes and the right classpath settings can prevent such errors in the nearest future. Feel free to drop your comments and questions in the section below.