How to Start a Standalone JavaFX Application from Another Instance within the Same Package?

How to Initialize a Standalone Application from another Instance when they are in the Same Package

Starting a standalone application from within another application, even when both applications belong to the same package, can seem straightforward but can be tricky to implement correctly. To begin with, an in-depth examination of the issue is necessary.

The problem arises when attempting to utilize the launch() method of an Application subclass from within another Application subclass. This approach triggers an error because the launch() method is intended to initiate the entire application and should not be invoked more than once.

To avoid this error, it is crucial to recognize that an Application subclass represents a complete application running within the Java Virtual Machine (JVM). Consequently, it should only be instantiated once per JVM for each separate application. Any reusable code should be moved to a separate class outside of the Application subclass.

Refactoring for Reusable Components

Instead of utilizing Application subclasses, a more flexible approach is to employ regular classes for individual components. These classes can then be instantiated and utilized as needed, enabling the creation of standalone applications or integration into larger applications.

public class FirstModule {    
    private BorderPane view;    
    public FirstModule() {        
        view = new BorderPane();        
        // ...         
    }    
    public Parent getView() {        
        return view;    
    }
}

public class CompositeModule {    
    private HBox view;    
    public CompositeModule() {        
        // ...         
    }    
    public Parent getView() {        
        return view;    
    }
}

Integration into Standalone Applications

To create independent applications, instantiate the required modules within an Application subclass.

public class FirstApplication extends Application {    
    @Override    
    public void start(Stage primaryStage) {        
        Scene scene = new Scene(new FirstModule().getView());        
        // ...    
    }
}

Integration into Larger Applications

To include these modules within larger applications, create a class that combines them.

public class CompositeApplication extends Application {    
    @Override    
    public void start(Stage primaryStage) {        
        Scene scene = new Scene(new CompositeModule().getView());        
        // ...    
    }
}

Conclusion

This technique offers greater flexibility and enables the development of reusable components, which can be utilized in various standalone applications or integrated into more extensive applications. This restructuring also aligns with the intended design of the JavaFX MVC architecture, separating the application logic from the user interface components.

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