BallAnimationTimerController.java

// BallAnimationTimerController.java
// Bounce a circle around a window using an AnimationTimer subclass. 
import java.security.SecureRandom;
import javafx.animation.AnimationTimer;
import javafx.fxml.FXML;
import javafx.geometry.Bounds;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Circle;
import javafx.util.Duration;

public class BallAnimationTimerController {
   @FXML private Circle c;
   @FXML private Pane pane;
   
   public void initialize() {
      SecureRandom random = new SecureRandom();
           
      // define a timeline animation
      AnimationTimer timer = new AnimationTimer() {
         int dx = 1 + random.nextInt(5);
         int dy = 1 + random.nextInt(5);
         int velocity = 60; // used to scale distance changes
         long previousTime = System.nanoTime(); // time since app launch

         // specify how to move Circle for current animation frame
         @Override
         public void handle(long now) {
            double elapsedTime = (now - previousTime) / 1000000000.0;
            previousTime = now;
            double scale = elapsedTime * velocity;

            Bounds bounds = pane.getBoundsInLocal();
            c.setLayoutX(c.getLayoutX() + dx * scale);
            c.setLayoutY(c.getLayoutY() + dy * scale);

            if (hitRightOrLeftEdge(bounds)) {
               dx *= -1;
            }

            if (hitTopOrBottom(bounds)) {
               dy *= -1;
            }
         }
      };
         
      timer.start();
   }
   
   // determines whether the circle hit left/right of the window
   private boolean hitRightOrLeftEdge(Bounds bounds) {
      return (c.getLayoutX() <= (bounds.getMinX() + c.getRadius())) ||
         (c.getLayoutX() >= (bounds.getMaxX() - c.getRadius()));
   }

   // determines whether the circle hit top/bottom of the window
   private boolean hitTopOrBottom(Bounds bounds) {
      return (c.getLayoutY() <= (bounds.getMinY() + c.getRadius())) ||
         (c.getLayoutY() >= (bounds.getMaxY() - c.getRadius()));
   }
}