BINARY SEARCH TREES - Introduction to Java Programming: Comprehensive Version - page 949

25.4 Tree Visualization and MVC
You can use recursion to display a binary tree.

Key
Point

Pedagogical Note
One challenge facing the data-structure course is to motivate students. Displaying a binary
tree graphically will not only help you understand the working of a binary tree but perhaps
also stimulate your interest in programming. This section introduces the techniques to
visualize binary trees. You can also apply visualization techniques to other projects.

How do you display a binary tree? It is a recursive structure, so you can display a binary tree
using recursion. You can simply display the root, then display the two subtrees recursively.
The techniques for displaying the Sierpinski triangle (Listing 18.9, SierpinskiTriangle.java)
can be applied to displaying a binary tree. For simplicity, we assume the keys are positive
integers less than 100 . Listings 25.9 and 25.10 give the program, and Figure 25.17 shows
some sample runs of the program.

F IGURE 25.17

A binary tree is displayed graphically.

L ISTING 25.9

BSTAnimation.java
1 import javafx.application.Application;
2 import javafx.geometry.Pos;
3 import javafx.stage.Stage;
4 import javafx.scene.Scene;
5 import javafx.scene.control.Button;
6 import javafx.scene.control.Label;
7 import javafx.scene.control.TextField;
8 import javafx.scene.layout.BorderPane;
9 import javafx.scene.layout.HBox;
10
11 public class BSTAnimation extends Application {
12 @Override // Override the start method in the Application class
13 public void start(Stage primaryStage) {

14 BST<Integer> tree = new BST<>(); // Create a tree

create a tree

15
16 BorderPane pane = new BorderPane();
17 BTView view = new BTView(tree); // Create a BTView
18 pane.setCenter(view);
19
20 TextField tfKey = new TextField();
21 tfKey.setPrefColumnCount( 3 );
22 tfKey.setAlignment(Pos.BASELINE_RIGHT);
23 Button btInsert = new Button( "Insert" );
24 Button btDelete = new Button( "Delete" );
25 HBox hBox = new HBox( 5 );
26 hBox.getChildren().addAll( new Label( "Enter a key: " ),

view for tree
place tree view