NoClassDefFoundError: wrong name: What's the Mismatch and How Do I Fix It?

NoClassDefFoundError: Understanding the Wrong Name Exception

Java programs often encounter the "NoClassDefFoundError: wrong name" exception when attempting to execute a compiled class file. This error can be confusing as the provided class name and path seem correct.

Cause:

The "wrong name" in the exception message indicates that the expected class name is different from the actual class name being loaded. This occurs when:

• Package Mismatch: The compiled class file includes a package, but it's not referenced when executing the class.
• Incorrect Path: The execution path is not set to the root of the package containing the class file.

Solution:

To resolve this error, take the following steps:

• Check Package Name: Ensure that the class file's package name matches the expected name.
• Set Execution Path: Navigate to the root folder containing the package of the class file. For instance, if the class is in the "clientrest" package, execute it from the folder containing the "clientrest" folder.
• Correct Class Name: When executing the class, use the fully qualified class name, including the package name. For example, for the "ClientREST" class in the "clientrest" package, execute:

java clientrest.ClientREST

Example:

Consider a "ClientREST" class in the "clientrest" package. If the class file is compiled in the "clientrest" folder, the correct execution path is the folder containing this folder. To run the class, use:

cd ../ # Move to the root package folder
java clientrest.ClientREST # Execute the class with a fully qualified name

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