import javafx.scene.input.MouseEvent;
import javafx.scene.shape.Rectangle;

public class Issue {
    public static void main(String[] args) {
        Rectangle r = new Rectangle();
        r.addEventHandler(MouseEvent.MOUSE_CLICKED, t -> System.out.println("dfdf"));
    }
}
//output
Issue.java:9: error: 'void' type not allowed here
        r.addEventHandler(MouseEvent.MOUSE_CLICKED, t -> System.out.println("dfdf"));
                                                                           
1 error