Chapter 18 Exercise 39, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

18.39 (Dragging the tree)
Revise Programming Exercise 18.38 to move the
tree to where the mouse is dragged.

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.input.KeyCode;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Line;
import javafx.stage.Stage;

public class Exercise_39 extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {

        TreePane pane = new TreePane();
        primaryStage.setScene(new Scene(pane));
        primaryStage.show();
    }

    class TreePane extends BorderPane {

        Label lblOrder = new Label("Enter Order:");
        TextField tfOrder = new TextField("0");
        Pane pane = new Pane();
        final int ANGLE = 25;
        double length = 50;

        int order;
        long count = 2;

        double startX;
        double startY;

        TreePane() {
            setMinSize(400, 400);

            HBox hBox = new HBox(10, lblOrder, tfOrder);
            hBox.setAlignment(Pos.BASELINE_CENTER);
            hBox.setPadding(new Insets(10));

            tfOrder.setPrefColumnCount(4);
            tfOrder.setAlignment(Pos.BASELINE_RIGHT);
            tfOrder.setOnKeyPressed(e -> {

                if (e.getCode() == KeyCode.ENTER) {
                    try {
                        order = Integer.parseInt(tfOrder.getText());
                    } catch (NumberFormatException ex) {
                        order = 0;
                        tfOrder.setText("0");
                    }
                } else if (e.getCode() == KeyCode.UP) {
                    order = Integer.parseInt(tfOrder.getText()) + 1;
                    tfOrder.setText(order + "");

                } else if (e.getCode() == KeyCode.DOWN) {
                    order = Math.max(Integer.parseInt(tfOrder.getText()) - 1, 0);
                    tfOrder.setText(order + "");

                }
                draw();
            });
            setBottom(hBox);
            setCenter(pane);

            pane.setMinSize(300, 300);
            pane.setOnMousePressed(e -> {
                startX = e.getX();
                startY = e.getY();
            });

            pane.setOnMouseDragged(e -> {
                    pane.setTranslateX(pane.getTranslateX() + e.getX() - startX);
                    pane.setTranslateY(pane.getTranslateY() + e.getY() - startY );
            });
            draw();
        }

        private void draw() {
            pane.getChildren().clear();
            Line line = new Line(200,  400, 200, 300);
            pane.getChildren().add(line);
            draw(line.getEndX(), line.getEndY(), 90, length, order);
        }

        private void draw(double x, double y, double angle, double length, int order) {

            if (order <= 0) return;

            double x2 = x + length * Math.cos(Math.toRadians(angle + ANGLE));
            double y2 = y - length * Math.sin(Math.toRadians(angle + ANGLE));
            double x3 = x + length * Math.cos(Math.toRadians(angle - ANGLE));
            double y3 = y - length * Math.sin(Math.toRadians(angle - ANGLE));
            pane.getChildren().add(new Line(x, y, x2, y2));
            pane.getChildren().add(new Line(x, y, x3, y3));

            draw(x2, y2, angle + ANGLE, length * 0.8, order - 1);
            draw(x3, y3, angle - ANGLE, length * 0.8, order - 1);
        }

    }

    public static void main(String[] args) {
        Application.launch(args);
    }
}