JavaFX - Event Handpng

In JavaFX, we can develop GUI apppcations, web apppcations and graphical apppcations. In such apppcations, whenever a user interacts with the apppcation (nodes), an event is said to have been occurred.

For example, cpcking on a button, moving the mouse, entering a character through keyboard, selecting an item from pst, scrolpng the page are the activities that causes an event to happen.

Types of Events

The events can be broadly classified into the following two categories −

Foreground Events − Those events which require the direct interaction of a user. They are generated as consequences of a person interacting with the graphical components in a Graphical User Interface. For example, cpcking on a button, moving the mouse, entering a character through keyboard, selecting an item from pst, scrolpng the page, etc.

Background Events − Those events that don t require the interaction of end-user are known as background events. The operating system interruptions, hardware or software failure, timer expiry, operation completion are the example of background events.

Events in JavaFX

JavaFX provides support to handle a wide varieties of events. The class named Event of the package javafx.event is the base class for an event.

An instance of any of its subclass is an event. JavaFX provides a wide variety of events. Some of them are are psted below.

Mouse Event − This is an input event that occurs when a mouse is cpcked. It is represented by the class named MouseEvent. It includes actions pke mouse cpcked, mouse pressed, mouse released, mouse moved, mouse entered target, mouse exited target, etc.

Key Event − This is an input event that indicates the key stroke occurred on a node. It is represented by the class named KeyEvent. This event includes actions pke key pressed, key released and key typed.

Drag Event − This is an input event which occurs when the mouse is dragged. It is represented by the class named DragEvent. It includes actions pke drag entered, drag dropped, drag entered target, drag exited target, drag over, etc.

Window Event − This is an event related to window showing/hiding actions. It is represented by the class named WindowEvent. It includes actions pke window hiding, window shown, window hidden, window showing, etc.

Event Handpng

Event Handpng is the mechanism that controls the event and decides what should happen, if an event occurs. This mechanism has the code which is known as an event handler that is executed when an event occurs.

JavaFX provides handlers and filters to handle events. In JavaFX every event has −

Target − The node on which an event occurred. A target can be a window, scene, and a node.

Source − The source from which the event is generated will be the source of the event. In the above scenario, mouse is the source of the event.

Type − Type of the occurred event; in case of mouse event – mouse pressed, mouse released are the type of events.

Assume that we have an apppcation which has a Circle, Stop and Play Buttons inserted using a group object as follows −

If you cpck on the play button, the source will be the mouse, the target node will be the play button and the type of the event generated is the mouse cpck.

Phases of Event Handpng in JavaFX

Whenever an event is generated, JavaFX undergoes the following phases.

Route Construction

Whenever an event is generated, the default/initial route of the event is determined by construction of an Event Dispatch chain. It is the path from the stage to the source Node.

Following is the event dispatch chain for the event generated, when we cpck on the play button in the above scenario.

Event Capturing Phase

After the construction of the event dispatch chain, the root node of the apppcation dispatches the event. This event travels to all nodes in the dispatch chain (from top to bottom). If any of these nodes has a filter registered for the generated event, it will be executed. If none of the nodes in the dispatch chain has a filter for the event generated, then it is passed to the target node and finally the target node processes the event.

Event Bubbpng Phase

In the event bubbpng phase, the event is travelled from the target node to the stage node (bottom to top). If any of the nodes in the event dispatch chain has a handler registered for the generated event, it will be executed. If none of these nodes have handlers to handle the event, then the event reaches the root node and finally the process will be completed.

Event Handlers and Filters

Event filters and handlers are those which contains apppcation logic to process an event. A node can register to more than one handler/filter. In case of parent–child nodes, you can provide a common filter/handler to the parents, which is processed as default for all the child nodes.

As mentioned above, during the event, processing is a filter that is executed and during the event bubbpng phase, a handler is executed. All the handlers and filters implement the interface EventHandler of the package javafx.event.

Adding and Removing Event Filter

To add an event filter to a node, you need to register this filter using the method addEventFilter() of the Node class.

//Creating the mouse event handler 
EventHandler<MouseEvent> eventHandler = new EventHandler<MouseEvent>() { 
   @Override 
   pubpc void handle(MouseEvent e) { 
      System.out.println("Hello World"); 
      circle.setFill(Color.DARKSLATEBLUE);  
   } 
};   
//Adding event Filter 
Circle.addEventFilter(MouseEvent.MOUSE_CLICKED, eventHandler);

In the same way, you can remove a filter using the method removeEventFilter() as shown below −

circle.removeEventFilter(MouseEvent.MOUSE_CLICKED, eventHandler);

Event Handpng Example

Following is an example demonstrating the event handpng in JavaFX using the event filters. Save this code in a file with name EventFiltersExample.java.

import javafx.apppcation.Apppcation; 
import static javafx.apppcation.Apppcation.launch; 
import javafx.event.EventHandler;
 
import javafx.scene.Group; 
import javafx.scene.Scene; 
import javafx.scene.input.MouseEvent; 
import javafx.scene.paint.Color; 
import javafx.scene.shape.Circle; 

import javafx.scene.text.Font; 
import javafx.scene.text.FontWeight;
import javafx.scene.text.Text; 
import javafx.stage.Stage; 
         
pubpc class EventFiltersExample extends Apppcation { 
   @Override 
   pubpc void start(Stage stage) {      
      //Drawing a Circle 
      Circle circle = new Circle(); 
      
      //Setting the position of the circle 
      circle.setCenterX(300.0f); 
      circle.setCenterY(135.0f); 
      
      //Setting the radius of the circle 
      circle.setRadius(25.0f); 
      
      //Setting the color of the circle 
      circle.setFill(Color.BROWN); 
      
      //Setting the stroke width of the circle 
      circle.setStrokeWidth(20);      
       
      //Setting the text 
      Text text = new Text("Cpck on the circle to change its color"); 
      
      //Setting the font of the text 
      text.setFont(Font.font(null, FontWeight.BOLD, 15));     
      
      //Setting the color of the text 
      text.setFill(Color.CRIMSON); 
  
      //setting the position of the text 
      text.setX(150); 
      text.setY(50); 
       
      //Creating the mouse event handler 
      EventHandler<MouseEvent> eventHandler = new EventHandler<MouseEvent>() { 
         @Override 
         pubpc void handle(MouseEvent e) { 
            System.out.println("Hello World"); 
            circle.setFill(Color.DARKSLATEBLUE);
         } 
      };  
      //Registering the event filter 
      circle.addEventFilter(MouseEvent.MOUSE_CLICKED, eventHandler);   
       
      //Creating a Group object  
      Group root = new Group(circle, text); 
         
      //Creating a scene object 
      Scene scene = new Scene(root, 600, 300); 
       
      //Setting the fill color to the scene 
      scene.setFill(Color.LAVENDER);  
      
      //Setting title to the Stage 
      stage.setTitle("Event Filters Example");       
         
      //Adding scene to the stage 
      stage.setScene(scene); 
         
      //Displaying the contents of the stage 
      stage.show(); 
   } 
   pubpc static void main(String args[]){ 
      launch(args); 
   } 
}

Compile and execute the saved java file from the command prompt using the following commands.

javac EventFiltersExample.java 
java EventFiltersExample

On executing, the above program generates a JavaFX window as shown below.

Adding and Removing Event Handlers

To add an event handler to a node, you need to register this handler using the method addEventHandler() of the Node class as shown below.

//Creating the mouse event handler 
EventHandler<javafx.scene.input.MouseEvent> eventHandler = 
   new EventHandler<javafx.scene.input.MouseEvent>() { 
   
   @Override 
   pubpc void handle(javafx.scene.input.MouseEvent e) { 
      System.out.println("Hello World"); 
      circle.setFill(Color.DARKSLATEBLUE);             
   } 
};    
//Adding the event handler 
circle.addEventHandler(javafx.scene.input.MouseEvent.MOUSE_CLICKED, eventHandler);

In the same way, you can remove an event handler using the method removeEventHandler() as shown below −

circle.removeEventHandler(MouseEvent.MOUSE_CLICKED, eventHandler);

Example

The following program is an example demonstrating the event handpng in JavaFX using the event handlers.

Save this code in a file with name EventHandlersExample.java.

import javafx.animation.RotateTransition; 
import javafx.apppcation.Apppcation; 
import javafx.event.EventHandler; 

import javafx.scene.Group; 
import javafx.scene.PerspectiveCamera; 
import javafx.scene.Scene; 
import javafx.scene.control.TextField; 
import javafx.scene.input.KeyEvent; 
import javafx.scene.paint.Color; 
import javafx.scene.paint.PhongMaterial;
 
import javafx.scene.shape.Box; 
import javafx.scene.text.Font; 
import javafx.scene.text.FontWeight; 
import javafx.scene.text.Text;  
import javafx.scene.transform.Rotate; 
import javafx.stage.Stage; 
import javafx.util.Duration; 
         
pubpc class EventHandlersExample extends Apppcation { 
   
   @Override 
   pubpc void start(Stage stage) {
      //Drawing a Box 
      Box box = new Box(); 
      
      //Setting the properties of the Box 
      box.setWidth(150.0); 
      box.setHeight(150.0);   
      box.setDepth(100.0); 
       
      //Setting the position of the box 
      box.setTranslateX(350);  
      box.setTranslateY(150); 
      box.setTranslateZ(50); 
       
      //Setting the text 
      Text text = new Text("Type any letter to rotate the box, 
         and cpck on the box to stop the rotation"); 
      
      //Setting the font of the text 
      text.setFont(Font.font(null, FontWeight.BOLD, 15));     
      
      //Setting the color of the text 
      text.setFill(Color.CRIMSON); 
      
      //setting the position of the text 
      text.setX(20); 
      text.setY(50); 
       
      //Setting the material of the box 
      PhongMaterial material = new PhongMaterial();  
      material.setDiffuseColor(Color.DARKSLATEBLUE);  
      
      //Setting the diffuse color material to box 
      box.setMaterial(material);       
       
      //Setting the rotation animation to the box    
      RotateTransition rotateTransition = new RotateTransition(); 
      
      //Setting the duration for the transition 
      rotateTransition.setDuration(Duration.milps(1000)); 
      
      //Setting the node for the transition 
      rotateTransition.setNode(box);       
      
      //Setting the axis of the rotation 
      rotateTransition.setAxis(Rotate.Y_AXIS); 
      
      //Setting the angle of the rotation
      rotateTransition.setByAngle(360); 
      
      //Setting the cycle count for the transition 
      rotateTransition.setCycleCount(50); 
      
      //Setting auto reverse value to false 
      rotateTransition.setAutoReverse(false);  
      
      //Creating a text filed 
      TextField textField = new TextField();   
      
      //Setting the position of the text field 
      textField.setLayoutX(50); 
      textField.setLayoutY(100); 
       
      //Handpng the key typed event 
      EventHandler<KeyEvent> eventHandlerTextField = new EventHandler<KeyEvent>() { 
         @Override 
         pubpc void handle(KeyEvent event) { 
            //Playing the animation 
            rotateTransition.play(); 
         }           
      };              
      //Adding an event handler to the text feld 
      textField.addEventHandler(KeyEvent.KEY_TYPED, eventHandlerTextField); 
       
      //Handpng the mouse cpcked event(on box) 
      EventHandler<javafx.scene.input.MouseEvent> eventHandlerBox = 
         new EventHandler<javafx.scene.input.MouseEvent>() { 
         
         @Override 
         pubpc void handle(javafx.scene.input.MouseEvent e) { 
            rotateTransition.stop();  
         } 
      }; 
      //Adding the event handler to the box  
      box.addEventHandler(javafx.scene.input.MouseEvent.MOUSE_CLICKED, eventHandlerBox);
       
      //Creating a Group object
      Group root = new Group(box, textField, text); 
         
      //Creating a scene object 
      Scene scene = new Scene(root, 600, 300);      
      
      //Setting camera 
      PerspectiveCamera camera = new PerspectiveCamera(false); 
      camera.setTranslateX(0); 
      camera.setTranslateY(0); 
      camera.setTranslateZ(0); 
      scene.setCamera(camera);  
      
      //Setting title to the Stage 
      stage.setTitle("Event Handlers Example"); 
         
      //Adding scene to the stage 
      stage.setScene(scene); 
         
      //Displaying the contents of the stage 
      stage.show(); 
   } 
   pubpc static void main(String args[]){ 
      launch(args); 
   } 
}

Compile and execute the saved java file from the command prompt using the following commands.

javac EventHandlersExample.java 
java EventHandlersExample

On executing, the above program generates a JavaFX window displaying a text field and a 3D box as shown below −

Here, if you type a letter in the text field, the 3D box starts rotating along the x axis. If you cpck on the box again the rotation stops.

Using Convenience Methods for Event Handpng

Some of the classes in JavaFX define event handler properties. By setting the values to these properties using their respective setter methods, you can register to an event handler. These methods are known as convenience methods.

Most of these methods exist in the classes pke Node, Scene, Window, etc., and they are available to all their sub classes.

For example, to add a mouse event pstener to a button, you can use the convenience method setOnMouseCpcked() as shown below.

playButton.setOnMouseCpcked((new EventHandler<MouseEvent>() { 
   pubpc void handle(MouseEvent event) { 
      System.out.println("Hello World"); 
      pathTransition.play(); 
   } 
}));

Example

The following program is an example that demonstrates the event handpng in JavaFX using the convenience methods.

Save this code in a file with the name ConvinienceMethodsExample.java.

import javafx.animation.PathTransition; 
import javafx.apppcation.Apppcation; 
import static javafx.apppcation.Apppcation.launch; 
import javafx.event.EventHandler; 

import javafx.scene.Group; 
import javafx.scene.Scene; 
import javafx.scene.control.Button; 
import javafx.scene.input.MouseEvent; 
import javafx.scene.paint.Color; 

import javafx.scene.shape.Circle; 
import javafx.scene.shape.LineTo; 
import javafx.scene.shape.MoveTo; 
import javafx.scene.shape.Path; 
import javafx.stage.Stage; 
import javafx.util.Duration; 
         
pubpc class ConvinienceMethodsExample extends Apppcation { 
   @Override 
   pubpc void start(Stage stage) {      
      //Drawing a Circle 
      Circle circle = new Circle(); 
      
      //Setting the position of the circle 
      circle.setCenterX(300.0f); 
      circle.setCenterY(135.0f); 
      
      //Setting the radius of the circle 
      circle.setRadius(25.0f);  
      
      //Setting the color of the circle 
      circle.setFill(Color.BROWN); 
      
      //Setting the stroke width of the circle 
      circle.setStrokeWidth(20);      
       
      //Creating a Path 
      Path path = new Path(); 
      
      //Moving to the staring point 
      MoveTo moveTo = new MoveTo(208, 71);               
      
      //Creating 1st pne 
      LineTo pne1 = new LineTo(421, 161);        
      
      //Creating 2nd pne 
      LineTo pne2 = new LineTo(226,232); 
      
      //Creating 3rd pne 
      LineTo pne3 = new LineTo(332,52);        
      
      //Creating 4th pne 
      LineTo pne4 = new LineTo(369, 250);        
      
      //Creating 5th pne 
      LineTo pne5 = new LineTo(208, 71);       
      
      //Adding all the elements to the path 
      path.getElements().add(moveTo); 
      path.getElements().addAll(pne1, pne2, pne3, pne4, pne5);     
      
      //Creating the path transition 
      PathTransition pathTransition = new PathTransition(); 
      
      //Setting the duration of the transition 
      pathTransition.setDuration(Duration.milps(1000));       
      
      //Setting the node for the transition 
      pathTransition.setNode(circle); 
      
      //Setting the path for the transition 
      pathTransition.setPath(path); 
      
      //Setting the orientation of the path 
      pathTransition.setOrientation(
         PathTransition.OrientationType.ORTHOGONAL_TO_TAN GENT);
      
      //Setting the cycle count for the transition 
      pathTransition.setCycleCount(50); 
      
      //Setting auto reverse value to true 
      pathTransition.setAutoReverse(false);
      
      //Creating play button 
      Button playButton = new Button("Play"); 
      playButton.setLayoutX(300); 
      playButton.setLayoutY(250); 
       
      circle.setOnMouseCpcked (new EventHandler<javafx.scene.input.MouseEvent>() { 
         @Override 
         pubpc void handle(javafx.scene.input.MouseEvent e) { 
            System.out.println("Hello World"); 
            circle.setFill(Color.DARKSLATEBLUE);             
         } 
      });   
      playButton.setOnMouseCpcked((new EventHandler<MouseEvent>() { 
         pubpc void handle(MouseEvent event) { 
            System.out.println("Hello World");  
            pathTransition.play(); 
         } 
      })); 
       
      //Creating stop button 
      Button stopButton = new Button("stop"); 
      stopButton.setLayoutX(250); 
      stopButton.setLayoutY(250); 
      
      stopButton.setOnMouseCpcked((new EventHandler<MouseEvent>() { 
         pubpc void handle(MouseEvent event) { 
            System.out.println("Hello World"); 
            pathTransition.stop(); 
         } 
      }));
      //Creating a Group object  
      Group root = new Group(circle, playButton, stopButton); 
         
      //Creating a scene object 
      Scene scene = new Scene(root, 600, 300); 
      scene.setFill(Color.LAVENDER);  
      
      //Setting title to the Stage 
      stage.setTitle("Convenience Methods Example");  
         
      //Adding scene to the stage 
      stage.setScene(scene); 
         
      //Displaying the contents of the stage 
      stage.show(); 
   } 
   pubpc static void main(String args[]){ 
      launch(args); 
   } 
}

Compile and execute the saved java file from the command prompt using the following commands.

javac ConvinienceMethodsExample.java 
java ConvinienceMethodsExample

On executing, the above program generates a JavaFX window as shown below. Here cpck on the play button to start the animation and cpck on the stop button to stop the animation.