How to Resolve 'Exception in Thread "Main" java.lang.NoSuchFieldError: Factory' in Java Applications?

What does the 'Exception in thread "main" java.lang.NoSuchFieldError: Factory' error message mean in Java applications?

public class Example {
    public static void main(String[] args) {
        // Attempt to access a field
        System.out.println(MyClass.Factory);
    }
}

The 'java.lang.NoSuchFieldError: Factory' error occurs at runtime when the Java Virtual Machine (JVM) could not find a field declaration that is expected to exist in a class. This is commonly due to version mismatches between compiled classes and the classes available at runtime.

// Example code illustrating how to properly access a field
public class MyClass {
    public static final String Factory = "ExampleFactory";
}

public class Example {
    public static void main(String[] args) {
        // Correctly accessing the Factory field
        System.out.println(MyClass.Factory);
    }
}

Causes

• The declared field 'Factory' is missing from the specified class at runtime, possibly due to a library update or removal.
• Classpath issues where an unintended version of a library is being loaded at runtime instead of the expected version.
• Build artifacts mismatch, where the code is compiled with one version of a dependency but runs with another.

Solutions

• Ensure that the correct version of the library containing the 'Factory' field is included in your classpath.
• Rebuild your project to ensure that there are no stale or conflicting class files.
• Check for dependency conflicts in your build tool (e.g., Maven, Gradle) and resolve them to include the correct versions of the libraries.

Mistake: Accessing a field or method that was removed in a newer library version.

Solution: Review the library's documentation or changelog to identify changes and update the code accordingly.

Mistake: Forgetting to include dependencies in your build configuration which results in runtime errors.

Solution: Ensure all required dependencies are correctly defined in your build tool (Maven, Gradle, etc.) and synced properly.

Mistake: Using an IDE that did not refresh properly leading to out-of-date cached versions of libraries.

Solution: Clean and rebuild the project in your IDE and ensure the classpath is up to date.