The error message "Error: Could not find or load main class" is a common issue faced by Java developers on the CentOS 7 operating system. This article provides a detailed guide on effectively resolving this issue and preventing its recurrence in the future.

Causes of the Error

The "Could not find or load main class" error occurs when the Java Runtime Environment (JRE) fails to locate the defined main class, which contains the public static void main(String[] args) method, during the execution of a Java application. The most common causes include:

• Incorrect path or class name specified in the command line.
• Missing or incorrectly configured CLASSPATH environment variable.
• Conflicts between JDK (Java Development Kit) and JRE versions.

Resolving the Issue

1. Verify the Correctness of the Path and Class Name

Start by verifying that you are launching the Java application with the exact name of the main class, including proper casing. Also, ensure that the path to the class is correctly specified. If you are launching the application from the command line, the command might look like this:

java -cp /path/to/your/classes com.package.MainClass

2. Set the CLASSPATH Environment Variable

The CLASSPATH environment variable plays a crucial role in determining where Java looks for classes. To check or set the CLASSPATH, use the following command in the terminal:

export CLASSPATH=$CLASSPATH:/path/to/your/files/*.jar:/additional/paths

After setting the variable, check if the issue is resolved.

3. Ensure Correct JDK and JRE Versions

Check if you have the correct JDK and JRE versions installed on CentOS 7 for your application. To display the currently installed version, use the following commands:

java -version
javac -version

If the versions do not match the requirements of your application, you may need to install or update the JDK/JRE.

4. Use Proper Folder Structure

Java expects classes to be organized into packages that correspond to folder structures. Make sure your .class files are placed in the correct folder structure matching the package name.

 

The "Could not find or load main class" error is often caused by incorrect path settings, class names, or environment configurations. By following the steps outlined above, you can successfully resolve this error and ensure smooth execution of your Java application on CentOS 7. If problems persist, it is recommended to delve deeper into the Java and CentOS documentation or seek assistance from community forums for further help.