How to Resolve JavaFX NoClassDefFoundError for javafx/application/Application?

What does the 'NoClassDefFoundError: javafx/application/Application' error mean and how can it be fixed?

System.out.println("Hello, JavaFX!");

The 'NoClassDefFoundError' in JavaFX typically indicates that the JavaFX application is not finding the necessary classes at runtime due to issues with the classpath setup or JavaFX library inclusion.

// Example of module-info.java for a modular JavaFX application
module my.application {
    requires javafx.controls;
    requires javafx.fxml;
    exports my.application;
}

Causes

• The JavaFX SDK is not added to the project's libraries.
• The project is not correctly configured to use JavaFX modules in the module system (Java 9 and above).
• The JavaFX runtime files are not on the classpath.
• For IDEs, the JavaFX Runtime is not configured properly in the run configurations.

Solutions

• Ensure that the JavaFX SDK is downloaded and correctly added to the project's libraries or dependencies.
• For modular applications, ensure that your `module-info.java` file includes the required `requires javafx.controls;` (and other modules as necessary).
• If using an IDE like IntelliJ IDEA or Eclipse, configure the project to include the JavaFX libraries in the build path.
• Use the proper VM options to include JavaFX modules when running the application. For example: ``` --module-path /path/to/javafx-sdk/lib --add-modules javafx.controls,javafx.fxml ```
• If you're using Maven or Gradle, ensure that the JavaFX dependencies are properly declared.

Mistake: Not including the JavaFX libraries in the classpath when running the application.

Solution: Make sure to add the JavaFX libraries to your IDE's library settings or correctly include the JavaFX modules if using JAR files.

Mistake: Using an outdated version of JavaFX that may not be compatible with your JDK.

Solution: Always make sure to use the latest version of JavaFX that matches your Java Development Kit version.