Practice Test for Objects (2.1-2.5)

2-16-1: A student has created a Liquid class. The class contains variables to represent the following.

• A double variable called boilingPoint to represent the boiling point of the liquid.

• A double variable called freezingPoint to represent at what temperature the liquid will freeze.

• A boolean variable called hasFrozen to indicate whether the liquid is now frozen.

The object liquid1 will be declared as type Liquid. Which of the following statements is accurate?

• An attribute of boilingPoint object is double.
• double is a data type, not an attribute.
• An instance of the liquid1 class is Liquid.
• The classname is Liquid and the object instance is liquid1.
• An attribute of the liquid1 object is freezingPoint.
• Correct!
• An instance of a Liquid object is hasFrozen.
• The classname is Liquid and the object instance is liquid1.
• An attribute of freezingPoint is liquid1.
• An attribute of liquid1 is freezingPoint.

2-16-2: A student has created an Artwork class. The class contains the following variables.

• A String variable called artist to represent the artist’s name

• A String variable called title to represent the artwork’s title

• A String variable called gallery to represent the gallery title

The object painting1 will be declared as type Artwork. Which of the following statements is true?

• painting1 is an instance of three String objects.
• The String variables are attributes of painting1.
• artist, title, and gallery are instances of the Artwork class.
• These are attributes.
• Artwork is an instance of the painting1 object.
• painting1 is an instance of Artwork.
• painting1 is an instance of the Artwork class.
• Correct!
• Artwork is an instance of three String objects.
• Artwork is the class name.

2-16-3: Which of the following code segments correctly creates an instance of a new Party object?

public class Party
{
    private int numInvited;
    private boolean partyCancelled;

    public Party()
    {
        numInvited = 1;
        partyCancelled = false;
    }

    public Party(int invites)
    {
        numInvited = invites;
        partyCancelled = false;
    }
}
I.   Party myParty;
II.  int classSize = 20;
     Party ourParty = new Party(classSize);
III. int numOfFriends = 6;
     Party yourParty = new Party(numOfFriends + 3.0);

• I only
• I needs to initialize the object variable with a call to new Party().
• I and II
• I needs to initialize the object variable with a call to new Party().
• II only
• Correct!
• II and III
• III calls the Party constructor with a double parameter instead of an int.
• I, II, and III
• I needs to initialize the object and III needs to use an int instead of a double as the parameter for the constructor.

2-16-4: Consider the following class. Which of the following code segments, when placed in a method in a class other than Liquid, will construct a Liquid object l with a boilingPoint of 98.6 ?

public class Liquid
{
    private double boilingPoint;
    private double freezingPoint;

    public Liquid()
    {
        boilingPoint = 0.0;
    }

    public Liquid(double b)
    {
        boilingPoint = b;
    }
}

• Liquid l = new Liquid(98.6);
• Correct
• new Liquid l = 98.6;
• new is incorrectly placed.
• Liquid l = new Liquid();
• This creates an object but it does not set its boiling point to 98.6.
• Liquid l = 98.6;
• The call to the constructor is missing.
• Liquid l = Liquid(98.6);
• The keyword new is missing.

2-16-5: Consider the following class. Assume that the Liquid object liquid has been properly declared and initialized in a method in a class other than Liquid. Which of the following statements are valid?

public class Liquid
{
  private double boilingPoint;
  private double freezingPoint;
  private double currentTemp;

  public Liquid(double b)
  {
    boilingPoint = b;
  }

  void lowerTemp()
  {
    currentTemp -= 10;
  }

  void raiseTemp()
  {
    currentTemp += 10;
  }

  void freeze()
  {
    currentTemp = freezingPoint;
  }
}

• liquid.freeze(80);
• Method freeze() does not have parameters.
• liquid.freeze();
• Correct
• liquid.increaseTemp();
• There is no method increaseTemp() in the Liquid class definition.
• liquidfreeze();
• The dot operator is required between the object name and the method name.
• liquid.freeze;
• Parentheses are required after a method name.

2-16-6: Consider the following class definition.

public class Dog
{
    public void bark()
    {
        System.out.print("Woof ");
    }

    public void wag()
    {
        System.out.print("Wag Tail ");
    }

    public void happy()
    {
        wag();
        bark();
    }
    /* Constructors not shown */
}

Which of the following code segments, if located in a method in a class other than Dog, will cause the message “Wag Tail Wag Tail Woof “ to be printed?

• Dog a = new Dog();
  a.bark();
  a.wag();
  

• This would print “Woof Wag Tail “

• Dog a = new Dog();
  Dog.happy();
  

• You must use the object a, not the class name Dog, to call its methods.

• Dog a = new Dog();
  a.happy();
  

• This would print out “Wag Tail Woof “.

• Dog a = new Dog();
  a.wag();
  a.happy();
  

• This would print out “Wag Tail Wag Tail Woof “;

• Dog a = new Dog();
  a.wag();
  

• This would just print “Wag Tail “.

2-16-7: Consider the following methods, which appear in the same class.

public void celsiusToFahrenheit(double cTemp)
{
    double fTemp = (cTemp * 9)/5 + 32;
    printTemperature(cTemp, fTemp);
}

public void printTemperature(double celsius, double fahrenheit)
{
    System.out.print(celsius + "-->" + fahrenheit);
}

Assume that the method call celsiusToFahrenheit(5) appears in a method in the same class. What is printed as a result of the method call?

• 5.0 –> 77.0

• (5 * 9)/5 + 32 = 41

• 41 –> 5

• Notice the order of parameters in printTemperature.

• celsius –> fahrenheit

• These are variables and their values would be printed.

• 5 –> 33.8

• (5 * 9)/5 + 32 = 41

• 5.0 –> 41.0

• Correct! (5 * 9)/5 + 32 = 41 and doubles print out with .0 at the end.

2-16-8: Consider the following methods, which appear in the same class.

public void calculatePizzaOrder(int numOfPeople, double slicesPerPerson)
{
    int numOfPizzas = (numOfPeople * slicesPerPerson)/8;
    /* INSERT CODE HERE */
}

public void printOrder(int number)
{
    System.out.println("Order " + number + " pizzas ");
}

What of the following lines would go into /* INSERT CODE HERE */ in line 4 in order to call the printOrder method to print the number of pizzas to order correctly?

• printOrder(numOfPizzas);

• Correct! If you had 8 people who want to eat 2 pizza slices each, numOfPizzas would be 8*2/8 = 2 pizzas, and printOrder would print out “Order 2 pizzas”.

• printOrder(numOfPeople);

• This would always print out an order of how many people you have instead of how many calculated pizzas.

• printOrder(2);

• This would always print out “Order 2 pizzas” instead of the calculated number of pizzas.

• printOrder(slicesPerPerson);

• This would always print out an order of how many slices per person instead of how many calculated pizzas.

• calculatePizzaOrder(numOfPizzas);

• This would not call the printOrder method.

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2-16-9: Consider the following method in the Movie class.

public double calculateMovieRating(int numOfPeople, double rating)
{ /*implementation not shown */}

Which of the following lines of code, if located in a method in the same class as calculateMovieRating, will compile without an error?

• int result = calculateMovieRating(234, null);

• The method returns a double which cannot be saved in an int variable.

• double result = calculateMovieRating(100.0, 3.0);

• The first parameter must be an int.

• int result = calculateMovieRating(455, false);

• The method returns a double which cannot be saved in an int variable.

• double result = calculateMovieRating(10, 4.0);

• Correct.

• double result = calculateMovieRating(10);

• The method has 2 parameters.

2-16-10: Consider the following methods, which appear in the same class.

public int oneThing(int i, int j)
{
    return i * j;
}

public int anotherThing(int i, int j)
{
    return i / j;
}

Which of the following statements, if located in a method in the same class, will initialize the variable x to 22?

• int x = oneThing(2, 10) + anotherThing(5, 2);
• oneThing(2,10) returns 2*10 = 20 and anotherThing(5,2) returns 5/2 = 2.5 truncated to 2 with integer division, which adds up to 22.
• int x = oneThing(10, 2) + anotherThing(2, 5);
• This would return 20 + 0 (which is 0.4 truncated) = 20.
• int x = oneThing(2, 10) + anotherThing(3, 2);
• This would return 20 + 1 (which is 1.5 truncated) = 21.
• int x = oneThing(6, 3) + anotherThing(2, 10);
• This would return 18 + 0 = 18.
• int x = oneThing(0, 2) + anotherThing(20, 1);
• This would return (0 * 2 = 0) + (20/1 = 20) = 20.

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