How to Fix the Could not find or load main class Main Error in Java

Discover how to resolve the `Could not find or load main class Main` error when running Java programs that require external libraries, with a focus on setting the classpath correctly.
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This video is based on the question https://stackoverflow.com/q/77086624/ asked by the user 'Ubuntu Learner' ( https://stackoverflow.com/u/16824403/ ) and on the answer https://stackoverflow.com/a/77087892/ provided by the user 'Maimoona Abid' ( https://stackoverflow.com/u/22213656/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Fix the Could not find or load main class Main Error in Java

Java programming often requires an understanding of how to manage classpaths and external libraries. A common issue that many developers face is the error: Could not find or load main class Main when trying to run a Java application that depends on external libraries like JDBC drivers. In this guide, we'll dive into how to address this problem effectively.

Understanding the Error

The error you're encountering is indicating that Java can't locate the class Main. This can arise due to several reasons, especially when your program relies on additional libraries. Let's walk through your situation step-by-step to understand what went wrong and how to fix it.

Your Java Program

You have a simple Java program designed to connect to a PostgreSQL database and execute a query. Here is the essential part of your code:

[[See Video to Reveal this Text or Code Snippet]]

Compiling Your Program

You compiled your program correctly using the following command:

[[See Video to Reveal this Text or Code Snippet]]

This step should have generated a Main.class file in the same directory. The compilation was successful, but when you tried to run your program, you encountered the exception related to the PostgreSQL driver.

The Root of the Problem

Upon trying to execute the program, this is the command you used:

[[See Video to Reveal this Text or Code Snippet]]

This resulted in a RuntimeException indicating that there was no suitable driver found for your PostgreSQL connection string. Therefore, you attempted to specify the classpath as follows:

[[See Video to Reveal this Text or Code Snippet]]

This resulted in the error: Could not find or load main class Main, which suggests your classpath setting was incomplete.

How to Fix the Error

To resolve your issue, you'll need to ensure that the classpath includes both the current directory (where your Main.class file is located) and the PostgreSQL JDBC JAR file. Here’s how to correctly set the classpath when running your program:

Updated Command

Use the following command to run your program:

[[See Video to Reveal this Text or Code Snippet]]

Important Notes

The . in the classpath refers to the current directory containing your compiled class files.

The : (or ; on Windows) acts as a separator between different paths in the classpath.

Always ensure that your JDBC driver (in this case, postgresql-42.6.0.jar) is in the specified directory.

Conclusion

By correcting your classpath and ensuring that both your current directory and the JDBC driver are included, you should be able to run your Java program without encountering the Could not find or load main class Main error.

Making sure that your Java environment is properly set up will make your coding experience much smoother and enjoyable. Happy coding!

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