Generate a Tree Recursion GUI

GenerateATree.java

package chapter18;

import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
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 GenerateATree extends Application {

	@Override // Override the start method in the Application class
	public void start(Stage primaryStage) {
		TreePane pane = new TreePane();
		TextField tfOrder = new TextField();
		tfOrder.setOnAction(e -> pane.setDepth(Integer.parseInt(tfOrder.getText())));
		tfOrder.setPrefColumnCount(4);
		tfOrder.setAlignment(Pos.BOTTOM_RIGHT);

		// Pane to hold label, text field, and a button
		HBox hBox = new HBox(10);
		hBox.getChildren().addAll(new Label("Enter an order: "), tfOrder);
		hBox.setAlignment(Pos.CENTER);

		BorderPane borderPane = new BorderPane();
		borderPane.setCenter(pane);
		borderPane.setBottom(hBox);

		// Create a scene and place it in the stage
		Scene scene = new Scene(borderPane, 200, 210);
		primaryStage.setTitle("Exercise18_39");
		primaryStage.setScene(scene);
		primaryStage.show();

		scene.widthProperty().addListener(ov -> pane.paint());
		scene.heightProperty().addListener(ov -> pane.paint());
	}

	/** Pane for displaying triangles */
	static class TreePane extends Pane {
		private int depth = 0;
		private double angleFactor = Math.PI / 5;
		private double sizeFactor = 0.58;

		private double startX = 0;
		private double startY = 0;

		public TreePane() {
			this.setOnMouseDragged(e -> {
				startX = e.getX();
				startY = e.getY() + 40;
				paint();
			});
		}

		public void setDepth(int depth) {
			this.depth = depth;
			paint();
		}

		public void paint() {
			getChildren().clear();
			startX = getWidth() / 2;
			startY = getHeight();
			paintBranch(depth, startX, startY - 10, getHeight() / 3, Math.PI / 2);
		}

		public void paintBranch(int depth, double x1, double y1, double length, double angle) {
			if (depth >= 0)
			{
				double x2 = x1 + Math.cos(angle) * length;
				double y2 = y1 - Math.sin(angle) * length;

				// Draw the line
				getChildren().add(new Line(x1, y1, x2, y2));
				// Draw the left branch
				paintBranch(depth - 1, x2, y2, length * sizeFactor, angle + angleFactor);
				// Draw the right branch
				paintBranch(depth - 1, x2, y2, length * sizeFactor, angle - angleFactor);
			}
		}
	}

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