Exercises for Chapter 5

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.

•First, two cards are dealt into each player’s hand. If the dealer’s hand has a value of 21 at this point, then the dealer wins. Otherwise, if the user has 21, then the user wins. (This is called a “Blackjack”.) Note that the dealer wins on a tie, so if both players have Blackjack, then the dealer wins.

•Now, if the game has not ended, the user gets a chance to add some cards to her hand. In this phase, the user sees her own cards and sees one of the dealer’s two cards. (In a casino, the dealer deals himself one card face up and one card face down. All the user’s cards are dealt face up.) The user makes a decision whether to “Hit”,

which means to add another card to her hand, or to “Stand”, which means to stop taking cards.

•If the user Hits, there is a possibility that the user will go over 21. In that case, the game is over and the user loses. If not, then the process continues. The user gets to decide again whether to Hit or Stand.

•If the user Stands, the game will end, but first the dealer gets a chance to draw cards. The dealer only follows rules, without any choice. The rule is that as long as the value of the dealer’s hand is less than or equal to 16, the dealer Hits (that is, takes another card). The user should see all the dealer’s cards at this point. Now, the winner can be determined: If the dealer has gone over 21, the user wins. Otherwise, if the dealer’s total is greater than or equal to the user’s total, then the dealer wins. Otherwise, the user wins.

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.

An applet version of this program can be found in the on-line version of this exercise. You might want to try it out before you work on the program.

Quiz on Chapter 5

(answers)

1.Object-oriented programming uses classes and objects. What are classes and what are objects? What is the relationship between classes and objects?

2.Explain carefully what null means in Java, and why this special value is necessary.

3.What is a constructor? What is the purpose of a constructor in a class?

4.Suppose that Kumquat is the name of a class and that fruit is a variable of type Kumquat. What is the meaning of the statement “fruit = new Kumquat();”? That is, what does the computer do when it executes this statement? (Try to give a complete answer. The computer does several things.)

5.What is meant by the terms instance variable and instance method ?

6.Explain what is meant by the terms subclass and superclass.

7.Modify the following class so that the two instance variables are private and there is a getter method and a setter method for each instance variable:

public class Player { String name;

int score;

}

8.Explain why the class Player that is defined in the previous question has an instance method named toString(), even though no definition of this method appears in the definition of the class.

9.Explain the term polymorphism.

10.Java uses “garbage collection” for memory management. Explain what is meant here by garbage collection. What is the alternative to garbage collection?

11.For this problem, you should write a very simple but complete class. The class represents a counter that counts 0, 1, 2, 3, 4, . . . . The name of the class should be Counter. It has one private instance variable representing the value of the counter. It has two instance methods: increment() adds one to the counter value, and getValue() returns the current counter value. Write a complete definition for the class, Counter.

12.This problem uses the Counter class from the previous question. The following program segment is meant to simulate tossing a coin 100 times. It should use two Counter objects, headCount and tailCount, to count the number of heads and the number of tails. Fill in the blanks so that it will do so: