Error: Could not find or load main class in IntelliJ IDE

Verifying IntelliJ's setup

When faced with "Could not find or load main class" error, evaluate your IntelliJ setup:

Validating JDK installation

Ensure the JDK is installed correctly and the correct version is in use:

• Open the Project Structure check the listed SDKs.
• Verify the correct Project SDK is selected.

Inspecting libraries and dependencies

Incorrect configurations can cause classpath issues:

• Go to Project Structure > Libraries and review the dependencies.
• Confirm that Module Dependencies are set right under Modules > Dependencies.

Reviewing the compiler output

Misaligned output settings can impede IntelliJ from finding generated class files:

• Open Project Structure > Project and make sure the output paths are good to go.

Addressing IntelliJ and cache hiccups

Sometimes resetting IntelliJ configurations or clearing bad cache can get you back on track:

Upgrading IntelliJ

Outdated versions of IntelliJ may cause compatibility problems:

• Go to Help > Check for Updates... and install any available updates.

Resetting IntelliJ configurations

Sometimes, completely resetting project files is necessary:

• Exit IntelliJ, delete the .idea folder and *.iml files.
• Re-open IntelliJ and import the project again.

Clearing caches and restarting

When IntelliJ's caches go corrupt, clearing them often helps:

• Use the Invalidate Caches / Restart... option (under File) for a fresh start.

Streamlining build and run configuration

After making sure of JDK installation and correct dependencies, focus on perfecting the build and run configurations:

Fine-Tuning build settings

IntelliJ’s build process may need some optimizing:

// Guess what? Annotation processors do not come with coffee.
EnableAnnotationProcessors();
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Setting run configuration

Make sure IntelliJ knows which main class to run:

// No, not Mainichi. We meant Main Class.
setMainClass("com.example.MainApp");
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Navigating through classpath and source recognition issues

When the main class isn't seen, issues could stem from incorrect source and classpath configuration.

Validating source folders

Ensure the source folders are recognized correctly by IntelliJ:

• In Project Structure > Modules, check if the source folders are categorized as Sources or Test Sources.

Verifying output folders

Class files should be generated in the specified output directory:

// I see source files, I see test files, where are the class files?!
checkOutputDirectory();
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Adapting to updates & remote changes

When updating your project or pulling changes:

• Rebuild the project so IntelliJ can see those shiny new changes.
• Synchronize your project files with your Gradle/Maven project.

// How to become popular among class files? Sync them up!
syncGradleProject();
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