Buttons not working on Program - multithreading

Question

I am trying to set up the buttons on the following program, but they will not control the program properly. I am not sure why they are not working. The reverse button works, but the start and stop buttons do not.
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Arc;
import javafx.scene.shape.ArcType;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
import javafx.util.Duration;
public class ch30 extends Application {
#Override // Override the start method in the Application class
public void start(Stage primaryStage) {
FanPane fan = new FanPane();
HBox hBox = new HBox(5);
Button btPause = new Button("Pause");
Button btResume = new Button("Resume");
Button btReverse = new Button("Reverse");
hBox.setAlignment(Pos.CENTER);
hBox.getChildren().addAll(btPause, btResume, btReverse);
BorderPane pane = new BorderPane();
pane.setCenter(fan);
pane.setBottom(hBox);
// Create a scene and place it in the stage
Scene scene = new Scene(pane, 200, 200);
primaryStage.setTitle("Exercise15_28"); // Set the stage title
primaryStage.setScene(scene); // Place the scene in the stage
primaryStage.show(); // Display the stage
//Runnable first = new Begin();
//Thread first = new Thread();
//t1.start();
Thread first = new Thread(new Runnable() {
#Override public void run() {
while (true) {
try {
//Pause
Thread.sleep(100);
} catch (InterruptedException ex) {
ex.printStackTrace();
}
Platform.runLater(new Runnable() {
#Override public void run() {
fan.move();
}
});
}
}
});
first.start();
//Timeline animation = new Timeline(
//new KeyFrame(Duration.millis(100), e -> fan.move()));
//animation.setCycleCount(Timeline.INDEFINITE);
//animation.play(); // Start animation
scene.widthProperty().addListener(e -> fan.setW(fan.getWidth()));
scene.heightProperty().addListener(e -> fan.setH(fan.getHeight()));
//btPause.setOnAction(e -> first.wait());
btResume.setOnAction(e -> first.start());
btReverse.setOnAction(e -> fan.reverse());
}
/**
* The main method is only needed for the IDE with limited
* JavaFX support. Not needed for running from the command line.
*/
public static void main(String[] args) {
launch(args);
}
}
class FanPane extends Pane {
private double w = 200;
private double h = 200;
private double radius = Math.min(w, h) * 0.45;
private Arc arc[] = new Arc[4];
private double startAngle = 30;
private Circle circle = new Circle(w / 2, h / 2, radius);
public FanPane() {
circle.setStroke(Color.BLACK);
circle.setFill(Color.WHITE);
getChildren().add(circle);
for (int i = 0; i < 4; i++) {
arc[i] = new Arc(w / 2, h / 2, radius * 0.9, radius * 0.9, startAngle + i * 90, 35);
arc[i].setFill(Color.RED); // Set fill color
arc[i].setType(ArcType.ROUND);
getChildren().addAll(arc[i]);
}
}
private double increment = 5;
public void reverse() {
increment = -increment;
}
public void move() {
setStartAngle(startAngle + increment);
}
public void setStartAngle(double angle) {
startAngle = angle;
setValues();
}
public void setValues() {
radius = Math.min(w, h) * 0.45;
circle.setRadius(radius);
circle.setCenterX(w / 2);
circle.setCenterY(h / 2);
for (int i = 0; i < 4; i++) {
arc[i].setRadiusX(radius * 0.9);
arc[i].setRadiusY(radius * 0.9);
arc[i].setCenterX(w / 2);
arc[i].setCenterY(h / 2);
arc[i].setStartAngle(startAngle + i * 90);
}
}
public void setW(double w) {
this.w = w;
setValues();
}
public void setH(double h) {
this.h = h;
setValues();
}
}

Answer 1

This should be done with a Timeline, I know it's your homework and for some crazy reason your homework has been specified to not use a Timeline. But for anybody else, don't do it this way, just use a Timeline.
That said...
You mention start and stop buttons of which you have none. I assume start means resume and stop means pause as those are the buttons you do have. So I will answer accordingly.
The easiest way to deal with this is to use a boolean variable to control whether or not the fan is moving.
Define a member of your application:
private boolean paused = false;
In your thread only move the fan if not paused:
Platform.runLater(() -> { if (!paused) fan.move(); });
Configure your buttons to set your flag:
btPause.setOnAction(e -> paused = true);
btResume.setOnAction(e -> paused = false);
I've just put the pause variable directly in the calling application, but you could encapsulate the pause status inside the fan object if you wished.
Normally when dealing with multi-threaded stuff you have to be careful about data getting corrupted due to race-conditions. For example, you would use constructs like AtomicBoolean or synchronized statements. But runLater puts everything on to the JavaFX application thread, so you don't necessarily need to worry about that.
There are alternate mechanisms you could use to ensure that your thread didn't keep looping and and sleeping, such as wait/notify or Conditions, but for a sample like this, you probably don't need that here.
Updated Application
Updated sample demonstrating the suggested modifications, tested on JDK 8u60, OS X 10.11.4.
public class ch30 extends Application {
private boolean paused = false;
#Override
public void start(Stage primaryStage) {
FanPane fan = new FanPane();
HBox hBox = new HBox(5);
Button btPause = new Button("Pause");
Button btResume = new Button("Resume");
Button btReverse = new Button("Reverse");
hBox.setAlignment(Pos.CENTER);
hBox.getChildren().addAll(btPause, btResume, btReverse);
BorderPane pane = new BorderPane();
pane.setCenter(fan);
pane.setBottom(hBox);
Thread first = new Thread(() -> {
while (true) {
try {
Thread.sleep(100);
} catch (InterruptedException ex) {
break;
}
Platform.runLater(() -> { if (!paused) fan.move(); });
}
});
first.setDaemon(true);
first.start();
btPause.setOnAction(e -> paused = true);
btResume.setOnAction(e -> paused = false);
btReverse.setOnAction(e -> fan.reverse());
Scene scene = new Scene(pane, 200, 200);
scene.widthProperty().addListener(e -> fan.setW(fan.getWidth()));
scene.heightProperty().addListener(e -> fan.setH(fan.getHeight()));
primaryStage.setScene(scene);
primaryStage.show();
}
}
Aside
Set the daemon status of your thread so that your application shuts down cleanly when somebody closes the main stage.
first.setDaemon(true);