labexercises2324/week1.java

import java.util.Calendar;
import java.util.Random;
import java.util.Scanner;
import java.util.concurrent.ThreadLocalRandom;

class runLabs {
    public static void main(String[] args) {
        // new Lab4();
        // new Lab5();
        new Lab6();
        // new Lab7();
    }
}

class Exercise {
    private int _exerciseNumber;

    public Exercise(int s) {
        this._exerciseNumber = s;
        this.printExercise();
    }

    public void printExercise() {
        String title = String.format("Starting exercise %s", this._exerciseNumber);

        System.out.println("-".repeat(title.length()));
        System.out.println(String.format("%s", title));
        System.out.println("-".repeat(title.length()));
    }

    public int get_exerciseNumber() {
        return _exerciseNumber;
    }

    public void set_exerciseNumber(int _exerciseNumber) {
        this._exerciseNumber = _exerciseNumber;
    }
}

class Lab {
    private int _labNumber;
    public Exercise currentExercise;

    public Lab(int lN) {
        String title = String.format("|Starting Lab %s|", lN);
        this._labNumber = lN;

        System.out.println("*".repeat(title.length()));
        System.out.println(title);
        System.out.println("*".repeat(title.length()));
    }

    public Exercise getCurrentExercise() {
        return currentExercise;
    }

    public void setCurrentExercise(Exercise currentSection) {
        this.currentExercise = currentSection;
    }

    public static void printSection(String section) {
        String title = String.format("Starting exercise %s", section);

        System.out.println("-".repeat(title.length()));
        System.out.println(String.format("%s", title));
        System.out.println("-".repeat(title.length()));
    }

    public int getLabNumber() {
        return this._labNumber;
    }
}

class Lab4 extends Lab {
    public Lab4() {
        super(4);
        // ex44();
        ex46();
    }

    // public static void main(String[] args) {
    // }

    public static void ex41() {
        String labSection = "4.1";
        // System.out.println(String.format("Starting section %s", labSection));
        printSection(labSection);

        int testYear1 = 1996; // true
        int testYear2 = 1997; // false
        int testYear3 = 2000; // true
        int testYear4 = 9332; // true
        int testYear5 = 1900; // false

        int randomYear = ThreadLocalRandom.current().nextInt(1, 9999 + 1);

        System.out.println(String.format("Testing %s", testYear1));
        System.out.println(String.format("%s", isLeap(testYear1)));

        System.out.println(String.format("Testing %s", testYear2));
        System.out.println(String.format("%s", isLeap(testYear2)));

        System.out.println(String.format("Testing %s", testYear3));
        System.out.println(String.format("%s", isLeap(testYear3)));

        System.out.println(String.format("Testing %s", testYear4));
        System.out.println(String.format("%s", isLeap(testYear4)));

        System.out.println(String.format("Testing %s", randomYear));
        System.out.println(String.format("%s", isLeap(randomYear)));

        System.out.println(String.format("Testing %s", testYear5));
    }

    public static void ex44() {
        String labSection = "4.4";
        printSection(labSection);

        // System.out.println("------------------------");
        // System.out.println("Starting lab section " + labSection);
        // System.out.println("------------------------");

        String month1 = "oct";
        int year1 = 2000;
        System.out.println(String.format("Month: %s\tYear: %d\tDays in month: %d",
                                         month1, year1, monthLen(month1, year1)));

        String month2 = "feb";
        int year2 = 2000;
        System.out.println(String.format("Month: %s\tYear: %d\tDays in month: %d",
                                         month2, year2, monthLen(month2, year2)));

        String month3 = "feb";
        int year3 = 1997;
        System.out.println(String.format("Month: %s\tYear: %d\tDays in month: %d",
                                         month3, year3, monthLen(month3, year3)));

        String month4 = "apr";
        int year4 = 2001;
        System.out.println(String.format("Month: %s\tYear: %d\tDays in month: %d",
                month4, year4, monthLen(month4, year4)));

    }

    /**
     * Lab section 4.5
     *
     * Write a program that can calculate how many whole years old someone is from
     * today’s date and their date of birth. You could store each date as three
     * integers (day, month, year)
     */
    public static void ex46() {
        String labSection = "4.6";
        printSection(labSection);
        // calculate whole years' old to date

        Calendar today = Calendar.getInstance();
        System.out.println("Today:\t" + today.getTime());

        Calendar dob1 = Calendar.getInstance();
        dob1.set(1990, 1, 1);

        System.out.println(String.format(
                "DOB 1:\t%s (difference:\t%d years)",
                                         dob1.getTime(),
                                         yearsOld(today, dob1)));

        Calendar dob2 = Calendar.getInstance();
        dob2.set(1994, 11, 22);

        System.out.println(String.format(
                "DOB 2:\t%s (difference:\t%d years)",
                                         dob2.getTime(),
                yearsOld(today, dob2)));

        Calendar dob3 = Calendar.getInstance();
        dob3.set(2000, 8, 19); // 23 years old

        System.out.println(String.format(
                "DOB 3:\t%s (difference:\t%d years)",
                                         dob3.getTime(),
                                         yearsOld(today, dob3)));

        Calendar dob4 = Calendar.getInstance();
        dob4.set(2000, 8, 20); // 23 years old

        System.out.println(String.format(
                "DOB 4:\t%s (difference:\t%d years)",
                                         dob4.getTime(),
                                         yearsOld(today, dob4)));

        Calendar dob5 = Calendar.getInstance();
        dob5.set(2000, 8, 21); // 22 years old

        System.out.println(String.format(
                "DOB 5:\t%s (difference:\t%d years)",
                                         dob5.getTime(),
                                         yearsOld(today, dob5)));

    }

    public static boolean isLeap(int year) {
        if (year % 4 != 0) {
            return false;
        } else {
            if (year % 100 == 0) {
                if (year % 400 == 0) {
                    return true;
                } else {
                    return false;
                }
            }
            return true;
        }
    }

    public static int monthLen(String month, int year) {
        if (month == "feb") {
            if (isLeap(year)) {
                return 29;
            } else {
                return 28;
            }
        } else if (
            (month == "apr") ||
            (month == "jun") ||
            (month == "sep") ||
            (month == "nov")) {
                return 30;
        } else {
            return 31;
        }
    }

    public static int yearsOld(Calendar laterDate, Calendar earlierDate)
    {
        int birthdayModifier = 0; // we assume they've had their birthday

        // we could probably do this with one if, checking DAY_OF_YEARs,
        // but since problem spec mentioned months and days we should really
        // pay attention to those
        if (earlierDate.get(Calendar.MONTH) > laterDate.get(Calendar.MONTH)) {
            // ie 8 (August) < 9 (September)
            birthdayModifier = -1; // not had their birthday yet so take 1 year off difference
        } else if (earlierDate.get(Calendar.MONTH) == laterDate.get(Calendar.MONTH)) {
            if (earlierDate.get(Calendar.DAY_OF_MONTH) > laterDate.get(Calendar.DAY_OF_MONTH)) {
                birthdayModifier = -1;
            }
        }

        return (int) Math.abs(laterDate.get(Calendar.YEAR) -
                              earlierDate.get(Calendar.YEAR) +
                              birthdayModifier
                              );
    }
}

/**
 * Keyboard input
 */
class Lab5 extends Lab {
    public Lab5() {
        super(5);
        // new five1();
        // new five5();
        // new five6();
        new five7();
    }

    class five1 extends Exercise {
        /**
         * We will now look at how we can get user input from the keyboard. We will
         * gloss over some
         * of the details here, but give you just the information you need to start
         * getting input and
         * processing it.
         */
        public five1() {
            super(1);
            Scanner keyboard = new Scanner(System.in);
            System.out.println("Please enter your name, followed by the return key?");
            String userEntry = keyboard.nextLine();
            System.out.println("Hello " + userEntry);
            System.out.println(String.format("%s", keyboard));

            System.out.println("Please enter your age");
            int userAge = keyboard.nextInt();
            // keyboard.nextLine();
            System.out.println("You are " + userAge + " years old");
            System.out.println("What is your favourite colour?");
            String col = keyboard.nextLine();
        }
    }

    /**
     * Prompt for input and summarise a circle
     *
     */
    class five5 extends Exercise {
        public five5() {
            super(5);
            userCircles();
        }

        public void userCircles() {
            Scanner kbIn = new Scanner(System.in);
            System.out.println(String.format("Please supply a radius, that I might describe you a circle"));
            double radius = kbIn.nextDouble();
            kbIn.nextLine();
            summariseCircle(radius);
            kbIn.close();
        }

        public void summariseCircle(double radius) {
            System.out.println(String.format("A circle with radius %.2f has circumference %.2f and radius %.2f",
                                             radius, compCircumference(radius), compArea(radius)));
        }

        public double compCircumference(double radius) {
            return (2 * Math.PI * radius);
        }

        public double compArea(double radius) {
            return (Math.PI * Math.pow(radius, 2));
        }
    }

    /**
     * {@link Scanner} understanding - actually process input
     *
     */
    class five6 extends Exercise {
        public five6() {
            super(6);
            getNameAndAge();
        }

        public void getNameAndAge() {
            String userName;
            int userAge;

            Scanner kbIn = new Scanner(System.in);
            System.out.println(String.format("Please enter your name and age separated by a space"));
            String userInput = kbIn.nextLine();
            Scanner inputOps = new Scanner(userInput);
            userName = inputOps.next();
            // TOASK -- is this what 'add an extra line that fixes this problem' was going for?
            while (!inputOps.hasNextInt()) {
                userName += " " + inputOps.next();
            }
            if (inputOps.hasNextInt()) {
                userAge = inputOps.nextInt();
            } else {
                userAge = 0;
            }

            System.out.println(String.format("Your name is %s and your age is %d",
                                             userName, userAge));
            kbIn.close();
            inputOps.close();
        }
    }

    /**
     * Get DOB from user input and calculate age using {@link Lab4.ex46()}
     *
     */
    class five7 extends Exercise {
        public five7() {
            super(7);
            showUserAge();
        }

        public void showUserAge() {
            Scanner userInput = new Scanner(System.in);
            System.out.println(String.format("Please input your DOB"));
            System.out.println(String.format("input format is YYYY M D"));
            String inputString = userInput.nextLine();

            Scanner processInput = new Scanner(inputString);

            int dobYear = processInput.nextInt();
            int dobMonth = processInput.nextInt();
            int dobDay = processInput.nextInt();
            // input sanitisation could be nice...

            Calendar userDOB = Calendar.getInstance();
            // recall months are zero-indexed!
            userDOB.set(dobYear, dobMonth-1, dobDay);

            Calendar today = Calendar.getInstance();

            System.out.println(String.format("Today:\t%s", today.getTime()));
            System.out.println(String.format(
                "DOB  :\t%s (difference: %d years)",
                                         userDOB.getTime(),
                                         Lab4.yearsOld(today, userDOB)));

            userInput.close();
            processInput.close();

        }
    }
}

/**
 * Loops
 */
class Lab6 extends Lab {
    public Lab6() {
        super(6);
        new six1();
        System.out.println(String.format("%n"));
        new six3();
        new six6();
        new six7();
        new six8();
        new six9();
        //  new six5();
    }

    /**
     * Times tables
     */
    class six1 extends Exercise {
        public six1() {
            super(1);
            int testNum = 6;
            System.out.println(String.format("Times table for %d:", testNum));
            writeTimesTable(7);
        }
    }

    class six3 extends Exercise {
        public six3() {
            super(3);
            int testNum = 13; // statistically the most prime of all numbers
            System.out.println(String.format("Testing primes..."));
            System.out.println(String.format("%d prime? %s", testNum, isPrime(testNum)));
            System.out.println(String.format("%d prime? %s", 23, isPrime(23)));
            System.out.println(String.format("%d prime? %s", 27, isPrime(27)));
            System.out.println(String.format("%d prime? %s", 28, isPrime(28)));
            System.out.println(String.format("%d prime? %s", 299, isPrime(299)));
            System.out.println(String.format("Generating primes..."));
            generatePrimes(1024);
            System.out.println(String.format("Done!%n"));
        }
    }

    /**
     * Number guessing game
     * Random number between 0 and 99, user guesses and is told higher / lower / correct
     */
    class six5 extends Exercise {
        private Random random = new Random();

        public six5() {
            super(5);
            numberGuessingGame();
        }

        public void numberGuessingGame() {
            final boolean SUPER_ADVANCED_AI = false; // true - simulated guesses, false - stdin
            final Scanner userInput = new Scanner(System.in);
            final int HIGHEST = 99;
            final int MAX_GUESSES = 10;
            int guess;

            int chosenNumber = random.nextInt(HIGHEST + 1);
            // super advanced AI section
            int maxPossible = HIGHEST + 1;
            int minPossible = 0;

            String guesses = "guess"; // for correct plurals

            if (SUPER_ADVANCED_AI) {
                guess = random.nextInt(HIGHEST+1);
            } else {
                guess = getUserGuess(userInput);
            }
            System.out.printf("Guessing...\t");
            for (int i = 0; i < MAX_GUESSES; i++ ) {
                System.out.printf("%d", guess);
                if (guess == chosenNumber) {
                    System.out.println(String.format("\nYou guessed right after %d %s! It was indeed %d",
                                                     i+1, guesses, chosenNumber));
                    userInput.close();
                    return;
                }
                guesses = "guesses"; // didn't get it on the first try
                if (guess < chosenNumber) {
                    System.out.printf("↑\t");
                    if (guess > minPossible) { minPossible = guess; }
                } else {
                    System.out.printf("↓\t");
                    if (guess < maxPossible) {
                        maxPossible = guess;
                    }
                }

                // The better approach is to guess halfway between minPossible and maxPossible
                // but that's kinda boring and robotic
                if (SUPER_ADVANCED_AI) {
                    guess = randomBetween(minPossible, maxPossible);
                } else {
                    guess = getUserGuess(userInput);
                }
                // TODO change the behaviour so it doesn't guess the same number in a row
            }

            System.out.println(String.format("\nThe answer was: %d. Better luck next time!", chosenNumber));
            userInput.close();

        }

        public int randomBetween(int min, int max) {
            if (min < 0) { min = 0; }
            if (max == 0) { return 0; }
            // System.out.printf(" random.nextInt(%d - %d) + %d ", max, min, min);
            return (random.nextInt(max - min) + min);
        }

        public int getUserGuess(Scanner userInput) {
                System.out.println(String.format("Please enter an integer between 0 and 99 to guess"));
                int guess = userInput.nextInt();
                userInput.nextLine();
                return guess;
        }
    }
    /**
     * Produce a number triangle
     *
     * eg:
     *    1
     *   2 2
     *  3 3 3
     * 4 4 4 4
     */
    class six6 extends Exercise {
        public six6() {
            super(6);
            numberTriangle(1);
            numberTriangle(4);
            numberTriangle(8);
            numberTriangle(29);
        }
    }

    class six7 extends Exercise {
        public six7() {
            super(7);
            describeDD(4.2, 1.6);
            describeDD(47.42, 7.9);
        }

        /** Simple exposition of double division
         * @param num1 Dividend
         * @param num2 Divisor
         */
        public void describeDD(double num1, double num2) {
            System.out.println(String.format("Double division of %.2f by %.2f:\t", num1, num2));
            DoubleDivisionResult result = doubleDivision(num1, num2);
            System.out.println(String.format("Quotient: %d (ie %.2f ✕ %d = %.2f)\tRemainder: %.2f",
                                             result.getQuotient(),
                                             num2,
                                             result.getQuotient(),
                                             (num2 * result.getQuotient()),
                                             result.getRemainder()));
        }
    }

    /**
     * Exercise 8 - String pad with specified character
     */
    class six8 extends Exercise {
        public six8() {
            super(8);
            describeStringPadding("NoNeed", 4, '!');
            describeStringPadding("Simon", 10, '@');
            describeStringPadding("Zaphod Beeblebrox", 42, '?');
            // describeStringPadding("Unicode", 10, '🤯'); aww
        }

        /**
         * Print for display what we're padding and the result
         *
         * @param toPad   The string to pad eg "Simon"
         * @param length  Desired length
         * @param padChar Character to pad with
         */
        public void describeStringPadding(String toPad, int paddedLength, char padChar) {
            System.out.println(String.format("Padding '%s' to length %d using padding character: %s",
                    toPad, paddedLength, padChar));
            System.out.println(stringLPad(toPad, paddedLength, padChar));
        }

        /**
         * (Left-)pad a string with the specific character
         *
         * @param toPad   The string to pad eg "Simon"
         * @param length  Desired length
         * @param padChar Character to pad with
         * @return The padded result
         */
        public static String stringLPad(String toPad, int paddedLength, char padChar) {
            // early out - return unmodified
            if (toPad.length() >= paddedLength) {
                return toPad;
            }
            // note that we could do this with String.repeat(), but since this is in the 'Loops'
            // part of the lab, we should probably do this with a loop
            // String paddedString = String.valueOf(padChar) + toPad;
            String paddedString = toPad;
            while (paddedString.length() < paddedLength) {
                paddedString = String.valueOf(padChar) + paddedString;
            }
            return paddedString;
        }

    }

    class six9 extends Exercise {
        private Random random = new Random(); // initialise once
        // see https://stackoverflow.com/a/35277291, to pick a random member of an enum, first convert it to an array
        private Throw[] throwsArray = Throw.values(); // can't call it 'throws' for obvious reasons

        final Throw randomThrow() {
            return throwsArray[random.nextInt(throwsArray.length)];
        }

        public six9() {
            super(9);
            Throw player1 = Throw.ROCK; // "Good ol' rock, nothing beats that"
            Throw player2 = randomThrow();
            System.out.println(String.format("Playing three games to warm up:"));
            playRockPaperScissors(player1, player2);
            player2 = randomThrow();
            playRockPaperScissors(player1, player2);
            player2 = randomThrow();
            playRockPaperScissors(player1, player2);
            System.out.println(String.format("Grand. Now it's your turn!"));
            player1 = getUserThrow();
            playRockPaperScissors(player1, player2);
        }
    }

    public Throw getUserThrow() {
        Scanner userInput = new Scanner(System.in);
        // Throw userThrow = null;

        while (true) {
            System.out.println(String.format("Please enter your throw:"));
            System.out.println(String.format("\t0 (rock), 1 (paper), 2 (scissors)"));
            System.out.println(String.format("\tor the word corresponding to the throw you'd like"));
            System.out.println(String.format("\t[q / quit] quits"));

            // check for number
            if (userInput.hasNextInt()) {
                int choiceNumber = userInput.nextInt();
                if ((choiceNumber < 0) || (choiceNumber > 2)) {
                    continue;
                } else {
                    userInput.close();
                    Throw[] throwsArray = Throw.values();
                    return throwsArray[choiceNumber];
                }
            } else if (userInput.hasNext()) {
                String choiceString = userInput.nextLine();
                switch (choiceString.toLowerCase()) {
                    case "rock":
                    case "stone":
                        userInput.close();
                        return Throw.ROCK;
                    case "paper":
                        userInput.close();
                        return Throw.PAPER;
                    case "scissors":
                        userInput.close();
                    return Throw.SCISSORS;
                case "q":
                case "quit":
                    userInput.close();
                    System.exit(0);
                default:
                    continue;
                }
            }
        }

    }

    public void playRockPaperScissors (Throw player1, Throw player2) {
        // slight semantic overload with throwing an error but I think that's the term
        // for plays in RPS
        String result;
        // early out - TOASK why this doesn't work when it works in a REPL!!
        // answered - umm, I forgot the else >_<
        if (player1 == player2) {
            result = "a draw";
        } else {
            switch (player1) {
                case ROCK:
                    if (player2 == Throw.SCISSORS) { result = "R>S Player 1 wins"; }
                    else { result = "R<P Player 2 wins"; }  // must be paper
                    break;
                case PAPER:
                    if (player2 == Throw.SCISSORS) { result = "P<S Player 2 wins"; }
                    else { result = "P>R Player 1 wins"; } // must be rock
                    break;
                case SCISSORS:
                    if (player2 == Throw.ROCK) { result = "S<R Player 2 wins"; }
                    else { result = "S>P Player 1 wins"; }  // must be paper
                    break;
                default:
                    result = "undefined behaviour";
                    break;
                }
        }
        writeRPSPlay(player1, player2, result);
    }

    public String getThrowName(Throw thrown) {
        // This could probably be done in the enum itself
        switch (thrown) {
        case ROCK: return six8.stringLPad("rock", 8, ' '); // pad to 'scissors' length so everything stays lined-up
        case PAPER: return six8.stringLPad("paper", 8, ' ');
        case SCISSORS: return "scissors";
        default: return "uh?";
        }
    }

    public void writeRPSPlay (Throw player1, Throw player2, String result) {
        System.out.printf("Player 1 throws... %s\t", getThrowName(player1));
        System.out.printf("Player 2 throws... %s\t", getThrowName(player2));
        System.out.println(String.format("The result is... %s", result));
    }

    enum Throw {
        ROCK,
        PAPER,
        SCISSORS
    }

    /* TOASK - is there a better way of returning multiple values in Java?
       à la python, ie: return (quotient, remainder)
    */

    /**
     * Wrapper class for returning results from double division
     */
    final class DoubleDivisionResult {
        private int quotient; // that's the number of times something goes into something else
        private double remainder; // that's the bit left over

        public DoubleDivisionResult(int quotient, double remainder) {
            this.quotient = quotient;
            this.remainder = remainder;
        }

        public int getQuotient() {
            return quotient;
        }

        public double getRemainder() {
            return remainder;
        }

    }

    /**
     * Perform 'double division'
     *
     * @param dividend Number to be divided
     * @param divisor Number to divide by
     * @return a {@link DoubleDivisionResult} with the (int) quotient and (double) remainder
     */
    public DoubleDivisionResult doubleDivision(double dividend, double divisor) {
        // example used is 4.2 and 1.6
        // should return 2 and 1.0
        final boolean DEBUG = false;
        double dQuotient = dividend / divisor;
        int iQuotient = (int)dQuotient;

        double remainder = dividend - (iQuotient * divisor);

        if (DEBUG) {
            System.out.println(String.format("float quotient: %.2f", dQuotient));
            System.out.println(String.format("int quotient: %d", iQuotient));
            // TOASK: is there a neater way to do this casting?
        }

        return new DoubleDivisionResult(iQuotient, remainder);
    }

    /**
     * @param num Size of triangle
     */
    public void numberTriangle(int num) {
        /* Observations:
           - for even-sized triangles, preceding number of spaces starts at n=rows and decrements
           - for even-sized triangles even numbers have odd spaces and vice versa

        TODO: handle multi-digit numbers
        */
        System.out.println(String.format(""));
        int spaces = num;
        for (int i = 1; i <= num; i++) {
            System.out.println(" ".repeat(spaces)
                               + String.format("%s ", i).repeat(i)
                               + " ".repeat(spaces-1)
                               );
            spaces--;
        }
        System.out.println(String.format(""));
    }

    /**
     * @param num The number to write the times table for
     * @param limit How many multiples to show
     */
    public void writeTimesTable(int num, int limit) {
        for (int i = 0; i < (limit + 1); i++) {
            System.out.printf("%d\t", num * i);
        }
    }

    /* TOASK - overload example.
       Question: is there a better way of doing optional function parameters in java?
    */
    /**
     * Write times table for num (10 entries)
     * @param num Number to show times table for
     */
    public void writeTimesTable(int num) {
        int DEFAULT_LIMIT = 10;
        writeTimesTable(num, DEFAULT_LIMIT);
    }

    public void generatePrimes(int upperLimit) {
        // handle 2 as a special case
        System.out.println(String.format("2"));
        // for (int i = 3; i <= upperLimit; i += 2) {
        for (int i = 2; i <= upperLimit; i++) {
            // TODO: figure out smarter way of doing this, I'm sure primes must be at least 6 apart...
            // Something about 2n ± 1 ?
            // seive of Erasthotenes ..?
            if (isPrime(i)) {
                System.out.printf("%d\t", i);
            }
        }
    }

    /**
     * But is it prime?
     * @param  num Integer to test for primality
     * @return if it's prime
     */
    public boolean isPrime(int num) {
        boolean DEBUG = false;
        if ((num == 2) || (num == 1)) {
            return true;
        }
        if (num % 2 == 0){
            return false;
        } else {
            int divisor = 3;
            double numSquareRoot = Math.sqrt((double)num);
            while (divisor <= numSquareRoot) {
                if (num % divisor == 0) {
                    return false;
                }
                divisor += 2;
                if (DEBUG) {
                    System.out.printf("%d\t", divisor);
                }
            }
            return true;
        }
    }
}

/**
 * String formatting
 *
 */
class Lab7 extends Lab {
        public Lab7() {
            super(7);
            writeTimesTable(8.24579, 10);
            writeTimesTable(93.12279, 22);
            writeTimesTable(193.12279, 22);
            writeTimesTable(13.9, 122);
        }

        /**
         * @param num   The number to write the times table for (0 <= num <= 99)
         * @param limit How many multiples to show (0 <= limit <= 99)
         */
        public void writeTimesTable(double num, int limit) {
            final double MINNUM = 0;
            final double MAXNUM = 99;
            final int MINLIMIT = 0;
            final int MAXLIMIT = 99;

            if ((num < MINNUM) || (num > MAXNUM)) {
                System.err.println(String.format("Please specify a number between %.2f and %.2f (supplied: %.2f)",
                                                 MINNUM, MAXNUM, num));
                return;
            }

            if ((limit < MINLIMIT) || (limit > MAXLIMIT)) {
                System.err.println(String.format("Please specify a limit between %d and %d (supplied: %d)",
                                                 MINLIMIT, MAXLIMIT, limit));
                return;
            }
            for (int i = 0; i < (limit + 1); i++) {
                // output specification:
                // ~~.~~~ x ~~ = ~~~~~.~~~
                System.out.printf("%2.3f x %02d = %5.3f%n", num, i, (num*i));
        }
    }
    }