GRAPHS AND APPLICATIONS - Introduction to Java Programming: Comprehensive Version - page 1043

(a) Circles are connected (b) Circles are not connected

F IGURE 28.14

You can apply DFS to determine whether the circles are connected.

We will write a program that lets the user create a circle by clicking a mouse in a blank
area that is not currently covered by a circle. As the circles are added, the circles are repainted
filled if they are connected or unfilled otherwise.
We will create a graph to model the problem. Each circle is a vertex in the graph. Two
circles are connected if they overlap. We apply the DFS in the graph, and if all vertices are
found in the depth-first search, the graph is connected.
The program is given in Listing 28.10.

L ISTING 28.10

ConnectedCircles.java
1 import javafx.application.Application;
2 import javafx.geometry.Point2D;
3 import javafx.scene.Node;
4 import javafx.scene.Scene;
5 import javafx.scene.layout.Pane;
6 import javafx.scene.paint.Color;
7 import javafx.scene.shape.Circle;
8 import javafx.stage.Stage;
9
10 public class ConnectedCircles extends Application {
11 @Override // Override the start method in the Application class
12 public void start(Stage primaryStage) {
13 // Create a scene and place it in the stage
14 Scene scene = new Scene( new CirclePane(), 450 , 350 );
15 primaryStage.setTitle( "ConnectedCircles" ); // Set the stage title
16 primaryStage.setScene(scene); // Place the scene in the stage
17 primaryStage.show(); // Display the stage
18 }
19
20 /** Pane for displaying circles */
21 class CirclePane extends Pane {
22 public CirclePane() {
23 this .setOnMouseClicked(e -> {
24 if (!isInsideACircle( new Point2D(e.getX(), e.getY()))) {
25 // Add a new circle
26 getChildren().add( new Circle(e.getX(), e.getY(), 20 ));
27 colorIfConnected();
28 }
29 });
30 }

create a circle pane

pane for showing circles

handle mouse clicked
is it inside another circle?

add a new circle
color if all connected