Chapter 9 Exercise 6, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

*9.6 (Stopwatch) Design a class named StopWatch . The class contains:
Private data fields startTime and endTime with getter methods.
A no-arg constructor that initializes startTime with the current time.
A method named start() that resets the startTime to the current time.
A method named stop() that sets the endTime to the current time.
A method named getElapsedTime() that returns the elapsed time for the
stopwatch in milliseconds.
Draw the UML diagram for the class and then implement the class. Write a test
program that measures the execution time of sorting 100,000 numbers using
selection sort.

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;
    }
}

public class Exercise_06 {

    public static void main(String[] args) {


        int[] randomArray = new int[100000];

        System.out.println("Creating an unsorted array of 100,000 numbers...");
        for (int i = 0; i < randomArray.length; i++) {
            randomArray[i] = (int) (Math.random() * 100000);
        }

        StopWatch stopWatch = new StopWatch();

        System.out.println("Sorting array using selection algorithm...");
        stopWatch.start();
        selectionSort(randomArray);
        stopWatch.stop();
        System.out.println("Time elapsed: " + stopWatch.getElapsedTime() + " milliseconds.");

        for (int i = 0; i < randomArray.length; i++) {

            System.out.printf("%6d ", randomArray[i]);
            if ((i + 1) % 10 == 0) System.out.printf("\n");

        }

    }

    // selection sort
    public static void selectionSort(int[] m) {

        for (int i = 0; i < m.length - 1; i++) {

            int currentMin = m[i];
            int currentIndex = i;

            for (int j = i + 1; j < m.length; j++) {

                if (currentMin > m[j]) {
                    currentMin = m[j];
                    currentIndex = j;
                }
            }

            if (currentIndex != i) {
                m[currentIndex] = m[i];
                m[i] = currentMin;
            }
        }
    }
}