cs106a – Assignment #5

The complete specification of assignment #5 can be found as part of the stream at iTunes.

Because this assignment is meant to teach arrays it uses them heavily. Thus create arrays to hold the values of the last roll of dice, to hold the categories which have already been used, and to hold to total and the sub scores. Because they are needed in several methods create them as instance variables. The dice array is filled with each (first) roll thus it can be initialized with the declaration. The others are instancialized and thus reset starting a new game. The array holding the used categories differs from the others as it is two dimensional where the rows represent the player and the columns the selected category.

The game itself consists of a fixed number of rounds which equals the number of scoring categories. In every round each player has a fixed number of rolls where the first one differs slightly from the following as all dice have to be rolled. After a players turn his/her score has to be updated, and at the end of the game the winner has to be selected.

	private int[] dice = new int[N_DICE];
	private boolean[][] usedCategories;
	private int[] upperScore;
	private int[] lowerScore;
	private int[] totalScore;

	private void playGame() {
		usedCategories = new boolean[nPlayers][N_CATEGORIES];
		upperScore = new int[nPlayers];
		lowerScore = new int[nPlayers];
		totalScore = new int[nPlayers];

		for (int round = 0; round < N_SCORING_CATEGORIES; round++) {
			for (int player = 0; player < nPlayers; player++) {	
				for (int roll = 1; roll < N_ROLLS; roll++) {					

The method for the first roll of dice waits for the player to click the roll button, rolls all dice and displays the result:

	private void firstRoll(int player) {
		String playerName = playerNames[player];				
		display.printMessage(playerName + "'s turn. Click \"Roll Dice\" button to roll the dice.");

For every other roll, the message differs slightly as it needs to mention that the player has to select which dice to re-roll. The method waits for this selection and rolls only the selected dice:

	private void furtherRoll() {
		display.printMessage("Select the dice you which to re-roll and click \"Roll Again\".");

Rolling dice means looping over all dice, checking if they have been selected to be rolled or if all dice should be rolled and assigning random numbers from 1 to 6 to them:

        private RandomGenerator rgen = new RandomGenerator();

	private void rollDice(boolean reRollAll) {
		for (int i = 0; i < N_DICE; i++) {
			if (reRollAll || display.isDieSelected(i)) 
				dice[i] = rgen.nextInt(1, N_FACES);

To update the score the player has to select a valid – meaning a not previously used – category. For this category the score needs to be calculated and displayed at the correct position. Depending on the category the upper or lower score has to be updated as well as the total. Furthermore depending if the upper score has reached a given limit its bonus has to be added:

	private void updateScore(int player) {
		int category;
		while (true) {
			display.printMessage("Select a category for this roll.");
			category = display.waitForPlayerToSelectCategory();
			if (!usedCategories[player][category]) break;			
		usedCategories[player][category] = true;

		int score = calculateScore(category);
		display.updateScorecard(category, player, score);
		if (category < UPPER_SCORE) {
			upperScore[player] += score;
			display.updateScorecard(UPPER_SCORE, player, upperScore[player]);
		} else {
			lowerScore[player] += score;
			display.updateScorecard(LOWER_SCORE, player, lowerScore[player]);
		totalScore[player] = upperScore[player] + lowerScore[player];
		if (upperScore[player] >= SCORE_UPPER_BONUS_LIMIT) {
			display.updateScorecard(UPPER_BONUS, player, SCORE_UPPER_BONUS);
			totalScore[player] += SCORE_UPPER_BONUS;
		display.updateScorecard(TOTAL, player, totalScore[player]);

Calculating the score depends on the chosen category, where most of them can use similar functionality:

	private int calculateScore(int category) {
		int score = 0;
		switch (category) {
		case ONES: 
			score = calculateSingleValues(1);
		case TWOS: 
			score = calculateSingleValues(2);
		case THREES: 
			score = calculateSingleValues(3);
		case FOURS: 
			score = calculateSingleValues(4);
		case FIVES: 
			score = calculateSingleValues(5);
		case SIXES:
			score = calculateSingleValues(6);
			score = calculateOfAKindValues(3);
		case FOUR_OF_A_KIND:
			score = calculateOfAKindValues(4);
		case YAHTZEE:
			score = calculateOfAKindValues(5);
		case CHANCE:
			score = calculateOfAKindValues(0);
		case FULL_HOUSE:
			score = calculateOfAKindValues(FULL_HOUSE);
			score = calculateOfAKindValues(SMALL_STRAIGHT);
			score = calculateOfAKindValues(LARGE_STRAIGHT);
		return score;

For the categories of the upper score the score needs simple to add the face values of the dice showing a particular value:

	private int calculateSingleValues(int value) {
		int result = 0;
		for (int i = 0; i < N_DICE; i++) {
			if (dice[i] == value) result += value;
		return result;

For the lower score categories it is necessary to first create a new array holding how often a certain face value shows. At the same time add up the face values and check if the given number of a kind has been reached. If so and if one of the “of a kind” categories has been selected the method can return the calculated result.

For a full house the newly created array needs to be looped, to check if one of the values equals 2 and another one 3.

To check for a straight the array needs to be inspected for the necessary count of consecutive values:

	private int calculateOfAKindValues(int number) {
		int result = 0;
		int value[] = new int[N_FACES];
		boolean isNumber = false;
		for (int i = 0; i < N_DICE; i++) {
			result += dice[i];
			if (++value[dice[i] - 1] >= number) isNumber = true;
		if (number == FULL_HOUSE) {
			boolean found2 = false;
			boolean found3 = false;
			for (int i = 0; i < N_FACES; i ++) {
				if (value[i] == 2) found2 = true;
				if (value[i] == 3) found3 = true;				
			if (found2 && found3) return SCORE_FULL_HOUSE;
		} else if ((number == SMALL_STRAIGHT) || (number == LARGE_STRAIGHT)) {
			int consecutives = 0;
			int maxConsecutives = 0;
			int previous = -1;
			for (int i = 0; i < N_FACES; i ++) {
				if ((value[i] > 0) && (i == previous + 1)) {
					if (consecutives > maxConsecutives) 
						maxConsecutives = consecutives;
				} else {
					consecutives = 0;
				previous = i;
			if ((number == SMALL_STRAIGHT) && (maxConsecutives >= 4)) {
			} else if ((number == LARGE_STRAIGHT) && (maxConsecutives == 5)) {

		if (!isNumber) return 0;
		if (number == 5) return SCORE_YAHTZEE;
		return result;

Finally finding the winner needs to loop over the array of the total scores and display the players with the highest score:

	private void findWinner() {
		String winner = "";
		String next = "";
		int winningScore = 0;
		for (int player = 0; player < nPlayers; player++) {	
			if (totalScore[player] == winningScore) {
				winner += next + playerNames[player];
			} else if (totalScore[player] > winningScore) {
				winner = playerNames[player];
				winningScore = totalScore[player];				
			next = " and ";
		display.printMessage("Congratulations, " + winner + ", you won with a total score of " + winningScore + "!");		

And not to forget, not to use actual values but constants in the code itself:

	private static final int N_ROLLS = 3;
	private static final int N_FACES = 6;
	private static final int SCORE_FULL_HOUSE = 25;
	private static final int SCORE_SMALL_STRAIGHT = 30;
	private static final int SCORE_LARGE_STRAIGHT = 40;
	private static final int SCORE_YAHTZEE = 50;
	private static final int SCORE_UPPER_BONUS_LIMIT = 63;
	private static final int SCORE_UPPER_BONUS = 35;

The code for this assignment is available on github.


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