Introduction to JavaFX Event Handling

Types of JavaFX Events

Foreground Events 

Events that need a user's direct interaction are known as foreground events. As a result of a user engaging with the graphical elements of a Graphical User Interface, they are produced. For instance, they are pressing a button, dragging the mouse, typing a character, choosing anything from a list, scrolling the website, etc. 

Background Events 

Background events take place in the background and don't involve the end-user. Examples of background events include operating system disruptions, hardware or software failure, timer expiration, and process completion. 

Events in JavaFX 

A variety of events can be handled with the help of JavaFX. The foundation class for an event is in the package JavaFX.event and called Event. Events are instances of any of their subclasses. The events available with JavaFX are rather diverse. The following is a list of some of them.

Event Handling

Let's continue the phases 

Also check out - Phases of Compiler

Phases of Event Handling in JavaFX

Each time an event is generated, JavaFX goes through the following phase:

Route Construction

Each time an event is generated, the default / initial route for the Event is determined by building the event dispatch chain. The path from the stage to the source node. Below is the event dispatch chain for the events generated when the play button is clicked.

Event Capturing Phase

The root node of the application transmits events after constructing the event dispatch chain. This Event spreads (top to bottom) to every delivery chain node. If any of these nodes has a filter registered for the created Event, it will be executed. The created event will be passed to the target node if no other node in the dispatch chain has a filter for it, and the target node will then process the Event.

Event Bubbling Phase

Events are transferred from the target node to the stage node during the event bubble phase (from bottom to top). A handler for the created Event will be performed if it has been registered by one of the nodes in the event dispatch chain. The procedure ends when the event reaches the root node if none of these nodes have a handler to handle it.

Event Handlers and Filters

Application logic for managing events is contained in event filters and handlers. Nodes can register with a variety of handlers and filters. When using parent-child nodes, you can give the parent a standard filter or handler that will be used by all child nodes by default.

As was previously indicated, this is a filter that is processed during the Event, and the handler is carried out during the Event's bubbling stage. In the JavaFX.event package, all handlers and filters implement the EventHandler interface.

Coded example for event handlers:

//inserting javafx modules
import javafx.application.Application; 
import static javafx.application.Application.launch; 
//initializing javafx event handlers
import javafx.event.EventHandler;
 //setting scene group
import javafx.scene.Group; 
//setting scene
import javafx.scene.Scene; 
import javafx.scene.input.MouseEvent; 
//setting colour pallets
import javafx.scene.paint.Color;
//choosing our shape in this case circle 
import javafx.scene.shape.Circle; 
//choosing text fonts
import javafx.scene.text.Font; 
//defining font weight
import javafx.scene.text.FontWeight;
import javafx.scene.text.Text;
//setting stage 
import javafx.stage.Stage; 
//defining our eventfilter class
public class EventFiltersExample extends Application { 
    //ovverriding
   @Override 
   public void start(Stage stage) {      
      //step towards creating a Circle 
      Circle circle = new Circle(); 
      
      //coordinates of the circle 
      circle.setCenterX(200.0f); 
      circle.setCenterY(135.0f); 
      
      //radius of circle
      circle.setRadius(30.0f); 
      
      //circle colour
      circle.setFill(Color.GOLD); 
      
      //stroke width of circle
      circle.setStrokeWidth(15);      
       
      //text to be displayed 
      Text text = new Text("Click the circle to change colour"); 
      
      //font weight
      text.setFont(Font.font(null, FontWeight.BOLD, 14));     
      
      //text colour
      text.setFill(Color.BLACK); 
  
      //ssetting position of text 
      text.setX(170); 
      text.setY(50); 
       
      //setting mouse handler event 
      EventHandler<MouseEvent> eventHandler = new EventHandler<MouseEvent>() { 
        //ovverriding
         @Override 
         //defining mouseevent handler
         public void handle(MouseEvent e) { 
            //printing out hello world
            System.out.println("Hello World"); 
            circle.setFill(Color.GOLD);
         } 
      };  
      //event filter registration
      circle.addEventFilter(MouseEvent.MOUSE_CLICKED, eventHandler);   
       
      //group object creation
      Group root = new Group(circle, text); 
         
      // scene object creation
      Scene scene = new Scene(root, 500, 250); 
       
      //Setting colour on change
      scene.setFill(Color.PURPLE);  
      
      //title on stge
      stage.setTitle("Event Filters");       
         
      //scene addition
      stage.setScene(scene); 
         
      //showing stage content
      stage.show(); 
   } 
   // defining main class
   public static void main(String args[]){ 
      launch(args); 
   } 
}

You can also try this code with Online Java Compiler

Run Code

Output:

Frequently Asked Questions

What is JavaFX?

JavaFX is a collection of graphics and media packages that allow programmers to design, build, debug, test, and deploy rich client applications that work reliably across several platforms.  

What is the JavaFX group?

The JavaFX group class is a component of JavaFX. A Group's node count is contained within it. A Group is not immediately resizable and will take on the aggregate boundaries of its offspring.

Which library is used for using JavaFX applications in Web browsers?

The Deployment Toolkit library is suggested for usage when launching a JavaFX application from a web page or embedding one there.

What are the three main components of a JavaFX application?

A JavaFX application typically consists of three main parts: Stage, Scene, and Nodes.

Conclusion

In this article, we have extensively discussed the details of the JavaFX Event Handling, its events, types, phases, and coded example.
We hope that this blog has helped you enhance your knowledge of JavaFX Event Handling, and if you want to learn more, check out our articles on JavaFX. 

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