e-chapter3.md

Chapter 3 Practice Exercises

Exercise 1

Design and implement a well-encapsulated abstraction to represent a Hand of cards in a player's hand as a Java class. A Hand should be able to contain between 0 and N cards, where N is a a parameterizable upper bound that will depend on the card game being played (e.g., 5 for Draw Poker, 13 for Bridge, etc.). Implement the following services on a Hand: add(Card), remove(Card), contains(Card), isEmpty(), size(), and isFull(). Find a way to provide access to the cards in the hand. Ensure that all the rules of encapsulation seen in Chapter 2 are respected and use design by contract to clarify valid and invalid inputs. Assume there are no duplicate cards and that there only ever exists only a single instance that represents a given card in a running program (more on this in Chapter 4).

Solution (and more)

Exercise 2

Make it possible to compare two Hand objects using the Comparable interface. Compare hands by increasing number of cards in the hand. Write a small program to test your class. You do not need to handle the case where the argument is null.

Solution (and more)

Exercise 3

Extend the code of Hand to make it possible to compare two Hand objects using the Comparator interface. Implement two different hand comparison strategies, by increasing or decreasing number of cards in the hand. Define static factory methods in the Hand class to return anonymous instances of comparators for the different comparison strategies. You do not need to handle the case where the argument is null.

Solution (and more)

Exercise 4

Draw a class diagram that represents the design of Hand realized as part of Exercises 1-3.

Solution

Exercise 5

Add a static factory method to class Hand that takes an Rank as parameter and returns an instance of a class that can compare hands in increasing number of cards of that rank in the hand. Clients should use this method to compare hands by number of aces, or number kings, or number of fours, etc. For example, if the client chooses to compare hands by number of aces, a hand with one ace should come before a hand with two aces. If two hands have the same number of aces, they should be considered equal and their order does not matter.

Solution

Exercise 6

Implement a UniversalComparator that stores the type of desired comparison from Exercise 3 as an enumerated type, and switches on that type. Note that this will require you to add a size() method to the interface of class Hand.

Solution

Exercise 7

Extend the design of Hand so that instances of Hand can be iterated over through the services declared in the Iterable interface.

Solution (and more)

Exercise 8

Draw a class diagram that illustrates how a Hand supports being iterated over. You can omit modeling the comparison behavior.

Solution

Exercise 9

Enhance class Hand so that it is kept in sorted order using a parameterizable sorting order. Use the Strategy pattern and dependency injection to allow clients to specify how cards should be sorted. The cards in the hand should be sorted according to the required order at all times.

Solution

Exercise 10

Following the Interface Segregation Principle, decompose the interface of class Hand so that clients only interested in checking the state of a hand (including iterating over its cards) can use a different interface from clients interested in modifying the hand. Create a UML class diagram of the design first, then code the solution.

Solution

Exercise 11 🔍

Review the code of class Foundations in the Solitaire application (Version 1.3) and create a class diagram that captures the main design decisions for this class.

Solution

Exercise 12 ⭐

Modify your Hand class to support a poker game and compare hands in terms of their strengths as poker hands. How should you deal with hands that do not have exactly five cards?

Hint: You can start by solving a less challenging variant of this problem by considering the following two simplifications. Once you have a working solution, try improving it to remove the simplifications.

• Only consider ace-low straights. So Ace, Two, Three, Four, Five is a straight, but ..., Queen, King, Ace is not. This will allow you to use the current ordering of Rank directly.
• Make the comparison based on only the poker hand type, without using the card value for breaking ties. So, for example, two hands that are three-of-a-kind are considered equal, despite being of a different rank.

No solution is provided for starred exercises.

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