How to Troubleshoot java.lang.ClassNotFoundException Errors in IntelliJ IDEA?

Debugging java.lang.ClassNotFoundException Errors in IntelliJ IDEA

When attempting to execute a Java program in IntelliJ IDEA, users may encounter the "java.lang.ClassNotFoundException" error. This exception indicates that the Java Virtual Machine (JVM) was unable to locate the specified class file in the classpath.

The cause of this error can be attributed to several factors:

• Incorrect main class selection: Ensure the correct main class is chosen in the Run/Debug configuration.
• Excluded compilation of class file: Verify that the affected class file (e.g., Table.java) is not inadvertently excluded from compilation due to errors or intentional exclusion.
• Missing "Build" step in execution configuration: Confirm that the "Build" step is included in the Before Launch steps of the Run/Debug configuration to ensure proper compilation.
• Misconfigured project: Check that the project has a defined Source root for the directory containing the subdirectory where the class file resides.
• Incorrect class package: Ensure the class file has a valid package statement and is located in the appropriate package structure.
• Invalid project path: Inspect the project path for colons or semicolons, which can disrupt the classpath.
• Digitally signed dependency: One of the dependent JAR files may have a digital signature, causing the generated artifact to retain a partial signature.
• Incorrect Java version: Verify that the project is configured with the appropriate Java version for compilation.
• Corrupted IDEA configuration files: Fix module file name references or create a new project to potentially resolve bugs in IDE configuration.
• Enabled Unicode UTF-8 setting: On Windows, disable the "Beta: Use Unicode UTF-8 for worldwide language support" setting to avoid interference.
• Invalid module dependency format: Ensure the project uses IntelliJ IDEA format dependencies instead of Eclipse format to prevent source root configuration loss.

Resolving the error typically involves correct configuration of the project, proper classpath management, and accurate run/debug configuration settings. By addressing these factors, users can effectively debug and resolve "java.lang.ClassNotFoundException" errors in IntelliJ IDEA.

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