Software Development & Fundamentals Microsoft Certification 98-361 TEST BANKS LESSON 2

Lesson 2: Introduction to Object-Oriented Programming

1. You are developing code for a method that calculates the discount for the items sold. You name the method CalculateDiscount. The method defines a variable, percentValue of the type double. You need to make sure that percentValue is accessible only within the CalculateDiscount method. What access modifier should you use when defining the percentValue variable?

a) private

b) protected

c) internal

d) public

Answer: a

Difficulty: Medium

Section Reference: Understanding Access Modifiers

The private modifier restricts the access to the class in which the member was defined. The protected modifier restricts the access to the containing class and to any class derived directly or indirectly from the containing class. The internal modifier restricts the access to the code in the same assembly. The public modifier does not restrict access.

2. You are developing code that defines an InitFields method. The method takes two parameters of data type double and does not return any value to the calling code. Which of the following code segments would you use to define the InitFields method?

a)      public double InitFields(double l, double w)

{

    length = l;

    width = w;

    return length * width;

}

b)      public void InitFields(double l, double w)

{

    length = l;

    width = w;

}

c)      public void InitFields(double l)

{

    length = l;

    width = l;

    return;

}

d)      public double InitFields(double l, double w)

{

    length = l;

    width = w;

}

Answer: b

Difficulty: Medium

Section Reference: Understanding Methods

If a method does not intend to return any value, its return type is specified by the keyword void. As the method takes two parameters of data type double, the parameter list must declare two variables of type double.

3. You created a class named GeoShape. You defined a method called Area in the GeoShape class. This method calculates the area of a geometric shape. You want the derived classes of GeoShape to supersede this functionality to support the area calculation of additional geometric shapes. When the method Area is invoked on a GeoShape object, the area should be calculated based on the runtime type of the GeoShape object. Which keyword should you use with the definition of the Area method in the GeoShape class?

a) abstract

b) virtual

c) new

d) overrides

Answer: b

Difficulty: Medium

Section Reference: Understanding Polymorphism

Use the virtual keyword to define the Area method. When a virtual method is invoked, the runtime type of the object is checked for an overriding member. The overriding member in the most derived class is called, which might be the original member, if no derived class has overridden the member.

4. Suppose that you defined a class Scenario that defines functionality for running customized pivot transform on large data sets. You do not want the functionality of this class to be inherited into derived classes. What keyword should you use to define the Scenario class?

a) sealed

b) abstract

c) private

d) internal

Answer: a

Difficulty: Medium

Section Reference: Understanding Inheritance

Use the sealed keyword to define the Scenario class. When applied to a class, the sealed modifier prevents other classes from inheriting from it.

5. You need to provide printing functionality to several of your classes. Each class’s algorithm for printing will likely be different. Also, not all the classes have an “is-a” relationship with each other. How should you support this functionality?

a) Add the print functionality to a base class with the public access modifier.

b) Have all classes inherit from an abstract base class and override the base-class method to provide their own print functionality.

c) Have all the classes inherit from a base class that provides the print functionality.

d) Create a common interface that all classes implement.

Answer: d

Difficulty: Medium

Section Reference: Understanding Interfaces

You should create a common interface that is implemented by all classes. Interfaces are used to establish contracts through which objects can interact with each other without knowing the implementation details.

6. You are writing code for a class named Book. You should be able to get a list of all books sorted by the author’s last name. You need to write code to define this behavior of a class. Which of the following class elements should you use?

a) method

b) property

c) event

d) delegate

Answer: a

Difficulty: Medium

Section Reference: Understanding Methods

A method defines the behavior of a class. You can write a method that returns a list of all books sorted by the author’s last name.

7. Suppose that you are writing code for a class named Product. You need to make sure that the data members of the class are initialized to their correct values as soon as you create an object of the Product class. The initialization code should always be executed. What should you do?

a) Create a static method in the Product class to initialize data members.

b) Create a constructor in the Product class to initialize data members.

c) Create a static property in the Product class to initialize data members.

d) Create an event in the Product class to initialize data members.

Answer: b

Difficulty: Medium

Section Reference: Understanding Classes

Constructors are special class methods that are executed when a new instance of a class is created. Constructors are used to initialize the object’s data members.

8. You are creating a new class named Sphere derived from the Shape class. The Shape class has the following code:

class Shape

{

    public virtual void Area()

    {

        // additional code...

    }

}

The Area method in the Shape class should provide new functionality but also hide the Shape class implementation of the Area method. Which code segment should you use to accomplish this?

a)      class Sphere : Shape

{

    public override void Area()

    {

        // additional code ...

    }

}

b)      class Sphere : Shape

{

    public new void Area()

    {

        // additional code ...

    }

}

c)      class Sphere : Shape

{

    public virtual void Area()

    {

        // additional code ...

    }

}

d)      class Sphere : Shape

{

    public static void Area()

    {

        // additional code ...

    }

}

Answer: b

Difficulty: Medium

Section Reference: Understanding Polymorphism

The new keyword creates a new member of the same name in the derived class and hides the base class implementation. The override keyword is not the correct answer because it replaces a base class member in a derived class.

9. You are creating a new class named Polygon. You write the following code:

class Polygon : IComparable

{

    public double Length { get; set; }

    public double Width { get; set; }

    public double GetArea()

    {

        return Length * Width;

    }

    public int CompareTo(object obj)

    {

        // to be completed

    }

}

You need to complete the definition of the CompareTo method to enable comparison of the Polygon objects. Which of the following code segments should you use?

a)      public int CompareTo(object obj)

{

    Polygon target = (Polygon)obj;

    double diff = this.GetArea() - target.GetArea();

    if (diff == 0)

        return 0;

    else if (diff > 0)

        return 1;

    else return -1;

}

b)      public int CompareTo(object obj)

{

    Polygon target = (Polygon)obj;

    double diff = this.GetArea() - target.GetArea();

    if (diff == 0)

        return 1;

    else if (diff > 0)

        return -1;

    else return 0;

}

c)      public int CompareTo(object obj)

{

    Polygon target = (Polygon)obj;

    if (this == target)

        return 0;

    else if (this > target)

        return 1;

    else return -1;

}

d)      public int CompareTo(object obj)

{

    Polygon target = (Polygon)obj;

    if (this == target)

        return 1;

    else if (this > target)

        return -1;

    else return 0;

}

Answer: a

Difficulty: Medium

Section Reference: Understanding Interfaces

The return value of the CompareTo method indicates the result of comparing the given parameter with the current object. According to the documentation of the CompareTo method,

• If the instance is equal to the parameter, CompareTo returns 0.
• If the parameter value is less than the instance or if the parameter is null, a positive value is returned.
• If the parameter value is greater than the instance, a negative value is returned.
• If the parameter is not of the compatible type, an ArgumentException is thrown.

10. You are writing code for a new method named Process:

void Draw(object o)

{

 

}

The code receives a parameter of type object. You need to cast this object into the type Polygon. At times, the value of o that is passed to the method might not be a valid Polygon value. You need to make sure that the code does not generate any System.InvalidCastException errors while doing the conversions. Which of the following lines of code should you use inside the Draw method to accomplish this goal?

a) Polygon p = (Polygon) o;

b) Polygon p = o is Polygon;

c) Polygon p = o as Polygon;

d) Polygon p = (o != null) ? o as Polygon : (Polygon) o;

Answer: c

Difficulty: Medium

Section Reference: Understanding Inheritance

The as operator is similar to the cast operation but, in the case of as, if the type conversion is not possible, null is returned rather than an exception raised. An exception may be generated with the code in the other answer choices.

11. You are writing code to handle events in your program. You define a delegate named PolygonHandler like this:

public delegate void PolygonHandler(Polygon  p);

You also create a variable of the PolygonHandler type as follows:

PolygonHandler handler;

Later in the program, you need to add a method named CalculateArea to the method invocation list of the handler variable. The signature of the CalculateArea method matches the signature of the PolygonHandler method. Any code that you write should not affect any existing event-handling code. Given this restriction, which of the following code lines should you write?

a) handler = new PolygonHandler(CalculateArea);

b) handler = CalculateArea;

c) handler += CalculateArea;

d) handler -= CalculateArea;

Answer: c

Difficulty: Medium

Section Reference: Understanding Events

You need to use the += operator rather than the simple assignment operator (=) to attach the event handler. By using the += operator, you ensure that this event handler will be added to a list of event handlers already attached with the event.

12. You are developing a C# application. You create a class of the name Widget. You use some third-party libraries, one of which also contains a class of the name Widget. You need to make sure that using the Widget class in your code causes no ambiguity. Which C# keyword should you use to address this requirement?

a) namespace

b) override

c) delegate

d) class

Answer: a

Difficulty: Medium

Section Reference: Understanding Namespaces

Use the namespace keyword. A namespace is a language element that allows you to organize code and create globally unique class names.

13. You are reviewing a C# program that contains the following class:

public class Rectangle

{

    public double Length {get; set;}

    public double Width { get; set; }

}

The program executes the following code as part of the Main method:

Rectangle r1, r2;

r1 = new Rectangle { Length = 10.0, Width = 20.0 };

r2 = r1;

r2.Length = 30;

Console.WriteLine(r1.Length);

What will be the output when this code is executed?

a) 10

b) 20

c) 30

d) 40

Answer: c

Difficulty: Medium

Section Reference: Understanding Values and References

The class Rectangle is a reference type, and the content of variable r1 is actually a reference to a memory location that holds a Rectangle object. So, after the r2 = r1; statement,

 both r1 and r2 point to the same memory location and in turn the same Rectangle object. In other words, there is only one rectangle object in memory, and both r1 and r2 are referring to it. When the Length property is modified, the change applies to both objects r1 and r2.

14. You are reviewing a C# program. The program contains the following class:

public struct Rectangle

{

    public double Length {get; set;}

    public double Width { get; set; }

}

The program executes the following code as part of the Main method:

Rectangle r1, r2;

r1 = new Rectangle { Length = 10.0, Width = 20.0 };

r2 = r1;

r2.Length = 30;

Console.WriteLine(r1.Length);

What will be the output when this code is executed?

a) 10

b) 20

c) 30

d) 40

Answer: a

Difficulty: Medium

Section Reference: Understanding Values and References

The struct is a value rather than a reference type, so both r1 and r2 maintain their own copies of data. So, after the r2 = r1; statement,  both r1 and r2 point to different memory locations. When the Length property for r2 object is modified, the change doesn’t affect the object r1.

15.  You are developing a C# application. You need to decide whether to declare a class member as static. Which of the following statements is true about static members of a class?

a) You can use the this keyword reference with a static method or property.

b) Only one copy of a static field is shared by all instances of a class.

c) Static members of a class can be used only after an instance of a class is created.

d) The static keyword is used to declare members that do not belong to individual objects but to a class itself.

Answer: d

Difficulty: Medium

Section Reference: Understanding Static Members

The static keyword is used to declare members that do not belong to individual objects but to a class itself. A static member cannot be referenced through an instance object. Instead, a static member is referenced through the class name. It is not possible to use the this keyword reference with a static method or property because the this keyword can be used only to access instance objects.

16. Suppose that you are a new C# developer and are reviewing object-oriented programming fundamentals. Which of the following statements is not true?

a) A class is a concrete instance of an object.

b) A class defines the template for an object.

c) A class is a definition of a new data type.

d) A constructor is used to initialize the data members of the object.

Answer: a

Difficulty: Medium

Section Reference: Understanding Static Members

A class is not a concrete instance of an object. Instead, an object is a concrete instance of a class. The facts in the other answer choices are all correct.

17.  You are C# developer who is developing a Windows application. You develop a new class that must be accessible to all the code packaged in the same assembly. Even the classes that are in the same assembly but do not directly or indirectly inherit from this class must be able to access the code. Any code outside the assembly should not be able to access the new class. Which access modifier should you use to declare the new class?

a) public

b) protected

c) private

d) internal

Answer: d

Difficulty: Medium

Section Reference: Understanding Access Modifiers

For the private access modifier, access is restricted only to the containing class. For the public access modifier, access is not restricted. For the protected access modifier, access is restricted only to the derived classes. For the internal access modifier, access is restricted only to the code in the same assembly.

18.  You are C# developer who is developing a Windows application. You need to provide a common definition of a base class that can be shared by multiple derived classes. Which keyword should you use to declare the new class?

a) virtual

b) sealed

c) interface

d) abstract

Answer: d

Difficulty: Medium

Section Reference: Understanding Inheritance

The abstract classes provide a common definition of a base class that can be shared by multiple derived classes. The sealed classes, on the other hand, provide complete functionality but cannot be used as base classes. The virtual and interface keywords cannot be applied to a class.

19. You are C# developer who is developing a Windows application. You write the following code:

Object o;

Later in the code, you need to assign the value in the variable o to an object of Rectangle type. You expect that at runtime the value in the variable o is compatible with the Rectangle class. However, you need to make sure that no exceptions are raised when the value is assigned. Which of the following code should you use?

a) Rectangle r = (Rectangle) o;

b) Rectangle r = o;

c) Rectangle r = o as Rectangle;

d) Rectangle r = o is Rectangle;

Answer: c

Difficulty: Medium

Section Reference: Understanding Inheritance

In case of simple cast operation, the runtime checks whether the value of the variable o is compatible with the Rectangle class. If, at execution time, the value of o is not compatible with the Rectangle class, the runtime throws a System.InvalidCastException. The as operator is similar to the cast operation but, in the case of as, if the type conversion is not possible, null is returned rather than an exception raised.

20. You are C# developer who is developing a Windows application. You need to provide derived classes the ability to share common functionality with base classes but still define their own unique behavior. Which object-oriented programming concept should you use to accomplish this functionality?

a) encapsulation

b) abstraction

c) polymorphism

d) inheritance

Answer: c

Difficulty: Medium

Section Reference: Understanding Polymorphism

Polymorphism is the ability of derived classes to share common functionality with base classes but still define their own unique behavior. Inheritance is a feature of object-oriented programming that allows you to develop a class once, and then reuse that code over and over as the basis of new classes.