Answers to Chapter 14 Review Questions
Chapter 14
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| 2: | Which capitalization style is recommended for
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| 3: | The following lines specify an instance variable declaration and what is meant to be a property with the task of allowing access to the instance variable speed from outside the object. However, the property definition has four problems that need to be fixed before it will work correctly. Find and fix the problems. private double speed; public double Speed { get { return speed; } } |
| A: | Change private to public, change int to double, remove the parentheses after Speed, and return speed not Speed. private double speed; public double Speed { get { return speed; } } |
| 4: | What is delayed initialization? When would you use it? Could delayed initialization also be implemented with accessor and mutator methods? |
| A: | Delayed initialization When a program does not initialize an instance variable until its associated get statement block is called the first time. Delayed initialization is used with instance variables that are resource demanding to update and rarely used. Delayed initialization can also be implemented with accessor and mutator methods. |
| 5: | The header of the following indexer declaration has three problems. What are they? static int myIndexer this [ ] { ... } |
| A: | An indexer cannot be static and does not have a name (as myIndexer); only the keyword this is used. At least one parameter must be specified inside the square brackets. The following is a valid indexer header: public int this [int index] { ... } |
| 6: | The Rainfall class contains an array with twelve elements. It also contains an indexer to access the array elements, which, like its array, is zero-based (first element is zero). A rainfallParis object is instantiated from the Rainfall class.
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| 7: | You have just finished implementing your Car class and are satisfied with the end result. During a quiet moment of contentment, your colleague suddenly suggests that to make the Car class perfect, you should include operator overloading for the class so it can be used with the + and - operators and support code like car3 = car1 + car2. Is this a good idea? Why or why not? |
| A: | This is not a good idea. We don't know intuitively how the Car objects are being added together, so including operator overloading for the Car class is likely to make the code more cryptic. |
| 8: | Why is operator overloading sometimes referred to as syntactic sugar? |
| A: | Operator overloading changes the code's appearance syntactically (sometimes it looks sweeter), but underneath the syntax surface, operator overloading is just another way of calling a method. |
| 9: | Recall the TimeSpan class from Listing 14.7. It already includes an operator + method to add two TimeSpan objects together and assign the result to a TimeSpan reference variable. Your colleague decides to include an operator - method so that TimeSpan objects can be subtracted. The following is the code he initially inserted into the TimeSpan class. It contains several flaws. Find them. private TimeSpan (TimeSpan timeSpan1, TimeSpan timeSpan2) { return (timeSpan1.Seconds timeSpan2.Seconds) } |
| A: | The operator - method must be public and static and include the operator keyword in front of the minus symbol. Furthermore, it must return a TimeSpan object not a value of type uint. The correct operator - method looks as follows: public static TimeSpan operator- (TimeSpan timeSpan1, TimeSpan timeSpan2) { TimeSpan differenceTimeSpan = new TimeSpan(); differenceTimeSpan.Seconds = timeSpan1.Seconds - timeSpan2.Seconds; return differenceTimeSpan; } |
| 10: | Among other program elements, your program contains the two classes EarthTimeSpan and BliposTimeSpan. Each class still contains an instance variable called totalSeconds of type uint. In this case, EarthTimeSpan contains a user-defined explicit conversion to the type short, and BliposTimeSpan contains a user-defined implicit conversion from the type decimal to BliposTimeSpan. myShort is a variable of type short and myDecimal is a variable of type decimal, earthTimeSpan1 is of type EarthTimeSpan and bliposTimeSpan1 is of type BliposTimeSpan. Determine whether each of the following statements is valid:
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| 11: | You are writing a program that will assist architects in drawing architectural plans. The program contains many classes that rely on manipulating two-dimensional drawings. One of these classes is called Bathroom, and it represents and manipulates drawings of bathrooms. It needs a class called Point to represent a point consisting of two coordinates. Would it be a good idea to nest this class in the Bathroom class? Why or why not? |
| A: | If there is a class called Bathroom, there are also likely to be classes with names such as Kitchen, Bedroom, and so on. All these classes have a fundamental need to manipulate two-dimensional drawings and therefore a need to use the Point class. Consequently, it is not a good idea to isolate the Point class inside Bathroom. Instead, it should be positioned where all these classes can access it and share the functionality provided by the Point class. |
Answers to Chapter 14 Programming Exercises
| 1: | Expand the Bicycle class of Listing 14.2 to contain an instance variable called age that represents the age of a Bicycle. Write a property that allows users of the Bicycle class to set and get the age instance variable. Include code that prevents the age instance variable from being assigned a negative value or a value greater than 200. Equip the Bicycle class with an instance variable called numberOfAgeAccesses to represent the number of times the age instance variable has been accessed. Include a property to access numberOfAgeAccesses. Should this latter property contain both a set and a get statement block? |
| A: | The following code could be inserted into the Bicycle class to answer Exercise 1. Note: This code does not compile separately. const byte MaxAge = 200; private byte age; private uint numberOfAgeAccesses = 0; public byte Age { get { numberOfAgeAccesses++; return age; } set { if (value > MaxAge) Console.WriteLine("Error. {0} exceeds the age limit {1}", value, MaxAge); else if (value < 0) Console.WriteLine("Error. {0} cannot be less than 0", value); else age = value; } } public uint NumberOfAgeAccesses { get { return numberOfAgeAccesses; } } |
| 2: | Write a class called Rainfall containing a one-dimensional array with 12 elements representing monthly rainfall measurements. Include the following features:
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| 3: | Allow two Rainfall objects to be added together with the + symbol. This should allow you to write the following: totalRainfall = rainfallA + rainfallB; where all three objects are of type Rainfall. totalRainfall should now hold an array where the first element holds the result of adding the first element of the array in rainfallA together with the first element of the array in rainfallB; the second element holds the result of adding the second element of the array in rainfallA together with the second element of the array in rainfallB, and so on. Allow two Rainfall objects to be compared with the < and > comparison operators. Let the average of the 12 elements in each of the two compared objects be the deciding factor. So, if rainfallA's average rainfall is greater than that of rainfallB, the following expression will be true: rainfallA > rainfallB and the next expression will be false: rainfallA < rainfallB Use the Average property that you have already written in exercise 2 to provide the necessary information for the comparison. Please save the code for use in exercise 4. |
| 4: | Write a class called RainfallQuarterly containing an array with four elements to store rainfall information on a quarterly basis. Write user-defined conversions between RainfallQuarterly and Rainfall going in both directions. A Rainfall object is converted to a RainfallQuartely object by adding together the first four array elements and assigning that value to the first array element of the RainfallQuarterly object, and so on. A RainfallQuartely object is converted to a Rainfall object by dividing the first array element by four and assigning this value to each of the first four elements in the Rainfall array, and so on. Should both conversions be explicit or just one of them, or perhaps both of them should be implicit? Why? Hint: In which conversion is data lost? In which conversion is it not lost? |
| A: | The following code could be an answer to Exercises 2 4. Note: This code does not compile independently. // This class is an answer to questions 2 and 3. class Rainfall { private uint[] rainfall = new uint[12]; private uint numberOfRainAccesses = 0; //Initialize the rainfall array public Rainfall() { for(int i = 0; i < 12; i++) { rainfall[i] = 0; } } public uint this [int index] { get { if (index < 1 || index > 12) { Console.WriteLine("Index is out of bounds"); return 0; } else { numberOfRainAccesses++; return rainfall[index - 1]; } } set { if (index < 1 || index > 12) Console.WriteLine("Index is out of bounds"); else rainfall[index - 1] = value; } } public uint NumberOfRainAccesses { get { return numberOfRainAccesses; } } public uint Average { get { uint sum = 0; for (int i = 0; i < 12; i++) { sum += rainfall[i]; } return (sum / 12); } } public static Rainfall operator+ (Rainfall rainfall1, Rainfall rainfall2) { Rainfall sumRainfall = new Rainfall(); //Add each corresponding month pair of the two //Rainfall objects together and assign the result //to the corresponding month of sumRainfall. for (int i = 1; i < 13; i++) { sumRainfall[i] = rainfall1[i] + rainfall2[i]; } return sumRainfall; } public static bool operator> (Rainfall rainfall1, Rainfall rainfall2) { if (rainfall1.Average > rainfall2.Average) return true; else return false; } public static bool operator< (Rainfall rainfall1, Rainfall rainfall2) { if (rainfall1.Average < rainfall2.Average) return true; else return false; } } //This class is written as an answer to programming exercise 4. class RainfallQuarterly { private uint[] rainQuarterly = new uint[4]; public uint this [int index] { get { if (index < 1 || index > 4) { Console.WriteLine("Index is out of bounds"); return 0; } else { return rainQuarterly[index - 1]; } } set { if (index < 1 || index > 4) Console.WriteLine("Index is out of bounds"); else rainQuarterly[index - 1] = value; } } //Implicit because no data is lost: For each quarter the three corresponding //months are added together and the sum assigned to this quarter. public static implicit operator RainfallQuarterly (Rainfall convertFrom) { RainfallQuarterly newRainQuarterly = new RainfallQuarterly(); uint tempSum; int tempIndex = 1; //For each quarter add the corresponding months together and //add this value to the quarter for (int i = 1; i < 5; i++) { tempSum = 0; for (int j = 1; j < 4; j++) { tempSum += convertFrom[tempIndex]; tempIndex++; } newRainQuarterly[i] = tempSum; } return newRainQuarterly; } //Explicit because data is lost when each quarterly amount is turned into //three monthly values all of the same size. public static explicit operator Rainfall (RainfallQuarterly convertFrom) { Rainfall newRainMonthly = new Rainfall(); int tempIndex = 1; uint tempAverage; //For each quarter calculate a monthly average rainfall //Assign this value to the months of this quarter for (int i = 1; i < 5; i++) { tempAverage = convertFrom[i] / 3; for (int j = 1; j < 4; j++) { newRainMonthly[tempIndex] = tempAverage; tempIndex++; } } return newRainMonthly; } } |
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