[ Chapter Index | Main Index ]

Programming Exercises for Chapter 5

This page contains several exercises for Chapter 5 in Introduction to Programming Using Java. For each exercise, a link to a possible solution is provided. Each solution includes a discussion of how a programmer might approach the problem and interesting points raised by the problem or its solution, as well as complete source code of the solution.

Exercise 5.1:

In all versions of the PairOfDice class in Section 5.2, the instance variables die1 and die2 are declared to be public. They really should be private, so that they would be protected from being changed from outside the class. Write another version of the PairOfDice class in which the instance variables die1 and die2 are private. Your class will need "getter" methods that can be used to find out the values of die1 and die2. (The idea is to protect their values from being changed from outside the class, but still to allow the values to be read.) Include other improvements in the class, if you can think of any. Test your class with a short program that counts how many times a pair of dice is rolled, before the total of the two dice is equal to two.

See the Solution

Exercise 5.2:

A common programming task is computing statistics of a set of numbers. (A statistic is a number that summarizes some property of a set of data.) Common statistics include the mean (also known as the average) and the standard deviation (which tells how spread out the data are from the mean). I have written a little class called StatCalc that can be used to compute these statistics, as well as the sum of the items in the dataset and the number of items in the dataset. You can read the source code for this class in the file StatCalc.java. If calc is a variable of type StatCalc, then the following methods are defined:

Typically, all the data are added one after the other by calling the enter() method over and over, as the data become available. After all the data have been entered, any of the other methods can be called to get statistical information about the data. The methods getMean() and getStandardDeviation() should only be called if the number of items is greater than zero.

Modify the current source code, StatCalc.java, to add instance methods getMax() and getMin(). The getMax() method should return the largest of all the items that have been added to the dataset, and getMin() should return the smallest. You will need to add two new instance variables to keep track of the largest and smallest items that have been seen so far.

Test your new class by using it in a program to compute statistics for a set of non-zero numbers entered by the user. Start by creating an object of type StatCalc:

StatCalc  calc;   // Object to be used to process the data.
calc = new StatCalc();

Read numbers from the user and add them to the dataset. Use 0 as a sentinel value (that is, stop reading numbers when the user enters 0). After all the user's non-zero numbers have been entered, print out each of the six statistics that are available from calc.

See the Solution

Exercise 5.3:

This problem uses the PairOfDice class from Exercise 5.1 and the StatCalc class from Exercise 5.2.

The program in Exercise 4.4 performs the experiment of counting how many times a pair of dice is rolled before a given total comes up. It repeats this experiment 10000 times and then reports the average number of rolls. It does this whole process for each possible total (2, 3, ..., 12).

Redo that exercise. But instead of just reporting the average number of rolls, you should also report the standard deviation and the maximum number of rolls. Use a PairOfDice object to represent the dice. Use a StatCalc object to compute the statistics. (You'll need a new StatCalc object for each possible total, 2, 3, ..., 12. You can use a new pair of dice if you want, but it's not necessary.)

See the Solution

Exercise 5.4:

The BlackjackHand class from Subsection 5.5.1 is an extension of the Hand class from Section 5.4. The instance methods in the Hand class are discussed in that section. In addition to those methods, BlackjackHand includes an instance method, getBlackjackValue(), that returns the value of the hand for the game of Blackjack. For this exercise, you will also need the Deck and Card classes from Section 5.4.

A Blackjack hand typically contains from two to six cards. Write a program to test the BlackjackHand class. You should create a BlackjackHand object and a Deck object. Pick a random number between 2 and 6. Deal that many cards from the deck and add them to the hand. Print out all the cards in the hand, and then print out the value computed for the hand by getBlackjackValue(). Repeat this as long as the user wants to continue.

In addition to TextIO.java, your program will depend on Card.java, Deck.java, Hand.java, and BlackjackHand.java.

See the Solution

Exercise 5.5:

Write a program that lets the user play Blackjack. The game will be a simplified version of Blackjack as it is played in a casino. The computer will act as the dealer. As in the previous exercise, your program will need the classes defined in Card.java, Deck.java, Hand.java, and BlackjackHand.java. (This is the longest and most complex program that has come up so far in the exercises.)

You should first write a subroutine in which the user plays one game. The subroutine should return a boolean value to indicate whether the user wins the game or not. Return true if the user wins, false if the dealer wins. The program needs an object of class Deck and two objects of type BlackjackHand, one for the dealer and one for the user. The general object in Blackjack is to get a hand of cards whose value is as close to 21 as possible, without going over. The game goes like this.

Two notes on programming: At any point in the subroutine, as soon as you know who the winner is, you can say "return true;" or "return false;" to end the subroutine and return to the main program. To avoid having an overabundance of variables in your subroutine, remember that a function call such as userHand.getBlackjackValue() can be used anywhere that a number could be used, including in an output statement or in the condition of an if statement.

Write a main program that lets the user play several games of Blackjack. To make things interesting, give the user 100 dollars, and let the user make bets on the game. If the user loses, subtract the bet from the user's money. If the user wins, add an amount equal to the bet to the user's money. End the program when the user wants to quit or when she runs out of money.

Here is an applet that simulates the program you are supposed to write. It would probably be worthwhile to play it for a while to see how it works.

See the Solution

Exercise 5.6:

Subsection 5.7.6 discusses the possibility of representing the suits and values of playing cards as enumerated types. Rewrite the Card class from Subsection 5.4.2 to use these enumerated types. Test your class with a program that prints out the 52 possible playing cards. Suggestions: You can modify the source code file Card.java, but you should leave out support for Jokers. In your main program, use nested for loops to generated cards of all possible suits and values; the for loops will be "for-each" loops of the type discussed in Subsection 3.4.4. It would be nice to add a toString() method to the Suit class from Subsection 5.7.6, so that a suit prints out as "Spades" or "Hearts" instead of "SPADES" or "HEARTS".

See the Solution

[ Chapter Index | Main Index ]