Visualizing DFS with a GUI version

MainGUI.java

import java.util.ArrayList;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Line;
import javafx.scene.shape.Polygon;
import javafx.scene.text.Font;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class MainGUI extends Application {

    ArrayList<Circle> nodes = new ArrayList<>();

    enum EdgeType {
        TREE,
        CROSS,
        BACK,
        FORWARD
    }

    @Override
    public void start(Stage stage) throws Exception {
        DiGraph diGraph = new DiGraph();
        System.out.println(diGraph);
        Pane root = new Pane();
        //  root.setStyle("-fx-background-color: #aaa");
        Scene scene = new Scene(root, 800, 600);
        stage.setScene(scene);
        stage.show();

        int nodesInOneLine = 4;

        for (int i = 0; i < diGraph.vertices.length; i++) {
            Circle circle = new Circle(15);
            double level = 0.98f / (diGraph.vertices.length);
            circle.setFill(new Color(
                    diGraph.dfs_numbers[i] * (level),
                    diGraph.dfs_numbers[i] * (level),
                    diGraph.dfs_numbers[i] * (level),
                    1.0f)
            );
            Text text = new Text("" + i);
            text.setFont(Font.font(17));
            text.setFill(Color.DARKORANGE);
            circle.setStroke(Color.DARKORANGE);
            text.layoutXProperty().bind(circle.centerXProperty().add(-text.getLayoutBounds().getWidth() / 2));
            text.layoutYProperty().bind(circle.centerYProperty().add(5));

            nodes.add(circle);
            root.getChildren().addAll(circle, text);
        }
        if (!diGraph.planarLayout) {
            int i = 0;
            for (Circle circle : nodes) {
                circle.setCenterX(400 + 250 * Math.cos(i * 2 * Math.PI / diGraph.vertices.length));
                circle.setCenterY(300 + 250 * (Math.sin(i * 2 * Math.PI / diGraph.vertices.length)));
                i++;
            }
        } else {
            int i = 0;
            int j = 0;
            for (Circle circle : nodes) {
                circle.setCenterX(50 + i * (750 / nodesInOneLine));
                circle.setCenterY(50 + j * (550 / nodesInOneLine));
                i++;
                if (i % nodesInOneLine == 0) {
                    j++;
                    i = 0;
                }
            }
        }
        diGraph.treeEdges.stream().forEach(edge -> {
            addEdge(root, edge, EdgeType.TREE);
        });
        diGraph.forwardEdges.stream().forEach(edge -> {
            addEdge(root, edge, EdgeType.FORWARD);
        });
        diGraph.backEdges.stream().forEach(edge -> {
            addEdge(root, edge, EdgeType.BACK);
        });
        diGraph.crossEdges.stream().forEach(edge -> {
            addEdge(root, edge, EdgeType.CROSS);
        });

    }

    void addEdge(Pane root, Edge edge, EdgeType type) {

        Line line = new Line();
        Circle u, v;
        u = nodes.get(edge.u);
        v = nodes.get(edge.v);
        line.setStartX(u.getCenterX());
        line.setStartY(u.getCenterY());
        line.setEndX(v.getCenterX());
        line.setEndY(v.getCenterY());
        Text t = new Text(type.name().toLowerCase() + " Edge");
        switch (type) {
            case TREE:
                t.setFill(Color.GREEN);
                line.setStroke(Color.GREEN);
                break;
            case BACK:
                t.setFill(Color.BLUE);
                line.setStroke(Color.BLUE);

                break;
            case FORWARD:
                t.setFill(Color.ORANGE);
                line.setStroke(Color.ORANGE);

                break;
            case CROSS:
                t.setFill(Color.RED);
                line.setStroke(Color.RED);

                break;
        }
        double arrowAngle = (Math.atan2(line.getEndY() - line.getStartY(), line.getEndX() - line.getStartX()));

        t.setLayoutX((line.getEndX() - line.getStartX()) / 2 + line.getStartX());
        t.setLayoutY((line.getEndY() - line.getStartY()) / 2 + line.getStartY());
        double scale = 2.5;
        Polygon arrowHead = new Polygon(-4.33 * scale, 2.5 * scale, 5.0 * scale, 0, -4.33 * scale, -2.5 * scale, -4.33 * scale, 2.5 * scale);
        arrowHead.setRotate(Math.toDegrees(arrowAngle));
        arrowHead.setLayoutX(line.getEndX() - 20 * Math.cos(arrowAngle));
        arrowHead.setLayoutY(line.getEndY() - 20 * Math.sin(arrowAngle));
        arrowHead.setFill(line.getStroke());
        root.getChildren().add(0, arrowHead);
        root.getChildren().add(0, line);
        root.getChildren().add(0, t);
    }

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