Chapter 15 Exercise 19, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

15.19 (Game: eye-hand coordination)
Write a program that displays a circle of radius 10 pixels filled
with a random color at a random location on a pane, as shown in
Figure 15.29b. When you click the circle, it disappears and a new
random- color circle is displayed at another random location. After twenty
circles are clicked, display the time spent in the pane, as shown in Figure 15.29c.

public class StopWatch {

    private long mStartTime;
    private long mEndTime;
    private long mElapsedPause;
    private int mLastSecond = 0;

    private boolean mIsOn;
    private boolean mIsPaused;

    private int mSeconds;
    private int mMinutes;
    private int mHours;

    public StopWatch() {
        mStartTime = System.currentTimeMillis();
    }

    public long getStartTime() {
        return mStartTime;
    }

    public long getEndTime() {
        return mEndTime;
    }

    public void start() {
        mIsOn = true;
        mStartTime = System.currentTimeMillis();
    }

    public void stop(){
        mEndTime = System.currentTimeMillis();
        mIsOn = false;
    }

    public long getElapsedTime() {
        return mEndTime - mStartTime;
    }

    public long peek() {
        return System.currentTimeMillis() - mStartTime;
    }
    public void pause() {
        mIsPaused = true;
        mElapsedPause = System.currentTimeMillis() - mStartTime;
    }

    public void resume() {
        mIsPaused = false;
        mStartTime = System.currentTimeMillis() - mElapsedPause;
    }

    public boolean isOn() {
        return mIsOn;
    }
    public boolean nextSecond() {
        updateTime();
        if (mSeconds != mLastSecond) {
            mLastSecond = mSeconds;
            return true;
        } else {
            return false;
        }
    }
    public boolean nextFiveSeconds() {
        updateTime();
        return mSeconds % 5 == 0;
    }

    public int getHour(){
        updateTime();
        return mHours;
    }

    public int getMinute(){
        updateTime();
        return mMinutes;
    }

    public int getSeconds(){
        updateTime();
        return mSeconds;
    }

    private void updateTime() {

        long currentTime = peek() / 1000;
        mSeconds = (int)(currentTime % 60);
        currentTime = currentTime / 60;

        mMinutes = (int) (currentTime % 60);
        currentTime = currentTime / 60;

        mHours = (int)(currentTime % 24);

    }

    @Override
    public String toString() {

        updateTime();
        String hours = getTimeFormat(mHours);
        String minutes = getTimeFormat(mMinutes);
        String seconds = getTimeFormat(mSeconds);

        return hours + ":" + minutes + ":" + seconds;
    }

    private String getTimeFormat(int time) {
        return (time > 9) ? time + "" : "0" + time;
    }

    public void reset(){
        stop();
        mHours = 0;
        mMinutes = 0;
        mSeconds = 0;
        mStartTime = 0;
        mEndTime = 0;
    }


    public boolean isPaused() {
        return mIsPaused;
    }
}

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.text.Text;
import javafx.stage.Stage;

public class Exercise_19 extends Application {

    static int circleCount = 0;

    @Override
    public void start(Stage primaryStage) {

        double width = 500;
        double height = 500;

        Circle c = new Circle(0, 0, 10);
        updateCircle(c);
        Pane pane = new Pane(c);
        Text count = new Text(50,50,circleCount + "");
        pane.getChildren().add(count);
        StopWatch timer = new StopWatch();
        c.setOnMouseClicked(e-> {

            if (!timer.isOn()) {
                timer.start();
            }
            if (circleCount < 19) {
                circleCount++;
                count.setText(circleCount + "");

                updateCircle(c);
            } else {
                timer.stop();
                pane.getChildren().remove(c);
                pane.getChildren().add(new Text(width / 2, height / 2, "Time spent is " +
                        timer.getElapsedTime() + " milliseconds"));
            }
        });
        primaryStage.setScene(new Scene(pane, width, height));
        primaryStage.setTitle("Game: eye-hand coordination");
        primaryStage.show();
    }

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

    private void updateCircle(Circle c) {

        double min = c.getRadius() + 5;
        double max = 500 - c.getRadius() - 5;

        c.setCenterX((Math.random() * (max - min) + min));
        max = 500
                - c.getRadius() - 5;
        c.setCenterY((Math.random() * (max - min) + min));

        c.setFill(new Color(Math.random(), Math.random(), Math.random(), 1));
    }


}