Deck 8: User-Defined Classes

Question 1

The components of a class are called fields.

Answer 1

False

Question 2

The non-static methods of a class are called instance methods.

Answer 2

True

Question 3

Modifiers are used to alter the behavior of the class.

Answer 3

True

Question 4

Not every user-defined class can override the default definition of the method toString because it is provided by Java.

Question 5

In deep copying, each reference variable refers to its own object.

Question 6

Given the declaration public class MyClass
{
private int x; public void print()
{
System.out.println("x = " + x);
} private void setX(int y)
{
x = y;
}
}MyClass myObject = new MyClass();The following statement is legal.myObject.setX(10);

Question 7

The methods of a class must be public.

Question 8

If the object is created in the definition of a method of the class, then the object can access both the public and private members of the class.

Question 9

An accessor method of a class first accesses the values of the data members of the class and then changes the values of the data members.

Question 10

Members of a class are usually classified into three categories: public, private, and static.

Question 11

If a member of a class is a private method, you can access it outside the class.

Question 12

Given the declaration public class MyClass
{
private int x; public void print()
{
System.out.println("x = " + x);
} private void setX(int y)
{
x = y;
}
}
MyClass myObject = new MyClass();The following statement is legal.myObject.print();

Question 13

When no object of the class type is instantiated, static data members of the class fail to exist.

Question 14

The method finalize automatically executes when the class object goes out of scope.

Question 15

A class and its members can be described graphically using Unified Modeling Language (UML) notation.

Question 16

In shallow copying, each reference variable refers to its own object.

Question 17

The default constructor executes when an object is instantiated and initialized using an existing object.

Question 18

The built-in operation that is valid for classes is the dot operator.

Question 19

A constructor has no type and is therefore a void method.

Question 20

Constructors are called like any other method.

Question 21

What is the default definition of the method toString?

A) There is no default definition; you must define the method yourself.
B) It creates a string that is the name of the object's class, followed by the hash code of the object.
C) It creates a string that is the name of the program.
D) It creates a string that is the name of the package, followed by the name of the class, followed by the hash of the object.

Question 22

Which of the following is a constructor without parameters?

A) copy constructor
B) default constructor
C) finalizer
D) modifier

Question 23

MysteryClass
-first: int
-second: double;
+MysteryClass()
+MysteryClass(int)
+MysteryClass(double);
+MysteryClass(int, double)
+setData(int, double): void
+getFirst(): int
+getSecond(): double
+doubleFirst(): int
+squareSecond(): double
+print(): void
+equals(MysteryClass): boolean
+makeCopy(MysteryClass): void
+getCopy():MysteryClass
Which of the following would be a default constructor for the class MysteryClass shown in the accompanying figure?

A) public MysteryClass(){ setData(0, 0.0); }
B) public MysteryClass(0, 0.0) { setData(); }
C) public MysteryClass(0) { setData(0, 0.0); }
D) private MysteryClass(10){ setData(); }

Question 24

In ____ copying, each reference variable refers to its own object.

A) shallow
B) deep
C) method
D) object

Question 25

Constructors have the same name as the ____.

A) member methods
B) data members
C) class
D) package

Question 26

Consider the following statements.public class Rectangle
{
Private double length;
Private double width; public Rectangle()
{
Length = 0;
Width = 0;
} public Rectangle(double l, double w)
{
Length = l;
Width = w;
} public void set(double l, double w)
{
Length = l;
Width = w;
} public void print()
{
System.out.println("Length = " + length
+ "; Width = " + width + "\n" +
+ " Area = " + area()
+ "; Perimeter = " + perimeter());
} public double area()
{
Return length * width;
} public void perimeter()
{
Return 2 * length + 2 * width;
} public void makeCopy(Rectangle otherRect)
{
Length = otherRect.length;
Width = otherRect.width
}
}Rectangle tempRect = new Rectangle(14, 10);
Rectangle newRect = new Rectangle(9, 5);What are the values of the instance variables of newRect after the following statement execute?newRect.makeCopy(tempRect);

A) length = 14; width = 10
B) length = 9; width = 5
C) length = 14; width = 5
D) None of these

Question 27

Classes that are defined within other classes are called inside classes.

Question 28

Class members consist of all of the following EXCEPT ____.

A) named constants
B) variable declarations
C) pre-defined methods
D) methods

Question 29

Every object has access to a reference to itself.

Question 30

MysteryClass
-first: int
-second: double;
+MysteryClass()
+MysteryClass(int)
+MysteryClass(double);
+MysteryClass(int, double)
+setData(int, double): void
+getFirst(): int
+getSecond(): double
+doubleFirst(): int
+squareSecond(): double
+print(): void
+equals(MysteryClass): boolean
+makeCopy(MysteryClass): void
+getCopy():MysteryClass
According to the UML class diagram in the accompanying figure, which of the following is a data member?

A) MysteryClass
B) print()
C) second
D) getFirst

Question 31

MysteryClass
-first: int
-second: double;
+MysteryClass()
+MysteryClass(int)
+MysteryClass(double);
+MysteryClass(int, double)
+setData(int, double): void
+getFirst(): int
+getSecond(): double
+doubleFirst(): int
+squareSecond(): double
+print(): void
+equals(MysteryClass): boolean
+makeCopy(MysteryClass): void
+getCopy():MysteryClass
According to the UML class diagram in the accompanying figure, which method is public and doesn't return anything?

A) getCopy()
B) print()
C) equals(MysteryClass)
D) doubleFirst()

Question 32

Consider the following class definition.public class Cylinder
{
Private double baseRadius;
Private double height; public Cylinder ()
{
BaseRadius = 0;
Height = 0;
} public Cylinder (double l, double h)
{
BaseRadius = l;
Height = h;
} public void set(double r, double h)
{
BaseRadius = r;
Height = h;
} public String toString()
{
Return (baseRadius + " " + height);
} public double SurfaceArea()
{
Return 2 * 3.14 * baseRadius * height;
} public double volume()
{
Return 3.14 * baseRadius * baseRadius * height;
}
}Suppose that you have the following declaration. Cylinder cyl = new Cylinder(1.5, 10);Which of the following sets of statements are valid in Java?
(i)
Cyl.surfaceArea();
Cyl.volume();
Cyl.print();
(ii)
Print(cyl.surfaceArea);
Print(cyl.volume());

A) Only (i)
B) Only (ii)
C) Both (i) and (ii)
D) None of these

Question 33

A mutator method of a class changes the values of the data members of the class.

Question 34

Consider the following statements.public class Circle
{
Private double radius; public Circle()
{
Radius = 0.0;
} public Circle(double r)
{
Radius = r;
} public void set(double r)
{
Radius = r;
} public void print()
{
System.out.println(radius + " " + area + " "
+ circumference);
} public double area()
{
Return 3.14 * radius * radius;
} public double circumference()
{
Return 2 * 3.14 * radius;
}}Circle myCircle = new Circle();
Double r;Which of the following statements are valid in Java? (Assume that console is Scanner object initialized to the standard input device.)
(i)
R = console.nextDouble();
MyCircle.area = 3.14 * r * r;
System.out.println(myCircle.area);
(ii)
R = console.nextDouble();
MyCircle.set(r);
System.out.println(myCircle.area());

A) Only (i)
B) Only (ii)
C) Both (i) and (ii)
D) None of these

Question 35

Consider the following class definition.public class Rectangle
{
Private double length;
Private double width; public Rectangle()
{
Length = 0;
Width = 0;
} public Rectangle(double l, double w)
{
Length = l;
Width = w;
} public void set(double l, double w)
{
Length = l;
Width = w;
} public void print()
{
System.out.println(length + " " + width);
} public double area()
{
Return length * width;
} public double perimeter()
{
Return 2 * length + 2 * width;
}
}Which of the following statements correctly instantiates the Rectangle object myRectangle?
(i) myRectangle = new Rectangle(12.5, 6);
(ii) Rectangle myRectangle = new Rectangle(12.5, 6);
(iii) class Rectangle myRectangle = new Rectangle(12.5, 6);

A) Only (i)
B) Only (ii)
C) Only (iii)
D) Both (ii) and (iii)

Question 36

Which of the following class definitions is correct in Java?
(i)
Public class Employee
{
Private String name;
Private double salary;
Private int id; public Employee()
{
Name = "";
Salary = 0.0;
Id = 0;
} public Employee(String n, double s, int i)
{
Name = n;
Salary = s;
Id = i;
} public void print()
{
System.out.println(name + " " + id + " " + salary);
}
}
(ii)
Public class Employee
{
Private String name;
Private double salary;
Private int id; public void Employee()
{
Name = "";
Salary = 0.0;
Id = 0;
} public void Employee(String n, double s, int i)
{
Name = n;
Salary = s;
Id = i;
}
Public void print()
{
System.out.println(name + " " + id + " " + salary);
}
}

A) Only (i)
B) Only (ii)
C) Both (i) and (ii)
D) Neither is correct

Question 37

MysteryClass
-first: int
-second: double;
+MysteryClass()
+MysteryClass(int)
+MysteryClass(double);
+MysteryClass(int, double)
+setData(int, double): void
+getFirst(): int
+getSecond(): double
+doubleFirst(): int
+squareSecond(): double
+print(): void
+equals(MysteryClass): boolean
+makeCopy(MysteryClass): void
+getCopy():MysteryClass
According to the UML class diagram in the accompanying figure, which of the following is a private member of the class MysteryClass?

A) doubleFirst
B) MysteryClass
C) second
D) print

Question 38

The abstract data type specifies the logical properties and the implementation details.

Question 39

In Java, the reference this is used to refer to only the methods, not the instance variables of a class.

Question 40

Which of the following is used to allocate memory for the instance variables of an object of a class?

A) the reserved word public
B) the reserved word static
C) the operator new
D) the operator +

Question 41

public class Secret
{
Private int x;
Private static int y;
Public static int count;
Public int z;
Public Secret()
{
X = 0;
Z = 1;
} public Secret(int a)
{
X = a;
} public Secret(int a, int b)
{
X = a;
Y = b;
} public String toString()
{
Return ("x = " + x + ", y = " + y + ",
Count = " + count);
} public static void incrementY()
{
Y++;
}
}What does the default constructor do in the class definition in the accompanying figure?

A) Sets the value of x to 0
B) Sets the value of z to 1
C) Sets the value of x to 0 and the value of z to 1
D) There is no default constructor.

Question 42

Which of the following words indicates an object's reference to itself?

A) this
B) that
C) public
D) protected

Question 43

What is the main use of inner classes?

A) To alter the behavior of the outer class
B) To handle events
C) To implement cascaded method calls
D) To provide information hiding

Question 44

When does the method finalize execute?

A) When the class object is created
B) At the start of every program
C) At the end of every program
D) When the class object goes out of scope

Question 45

ADTs illustrate the principle of ____.

A) information hiding
B) privacy
C) encapsulation
D) overloading

Question 46

Suppose that Book is class with two instance variables-name of type String and numOfBooks of type int. Which of the following would be appropriate syntax for the heading of a copy constructor for the class called Book?

A) public Book(String n, int num)
B) public Book()
C) public Book(Book b)
D) public copyBook(String n, int num)

Question 47

How many finalizers can a class have?

A) zero
B) one
C) two
D) Any number

Question 48

public class Secret
{
Private int x;
Private static int y;
Public static int count;
Public int z;
Public Secret()
{
X = 0;
Z = 1;
} public Secret(int a)
{
X = a;
} public Secret(int a, int b)
{
X = a;
Y = b;
} public String toString()
{
Return ("x = " + x + ", y = " + y + ",
Count = " + count);
} public static void incrementY()
{
Y++;
}
}Based on the class in the accompanying figure, which of the following statements is illegal?

A) Secret.incrementY();
B) Secret.count++;
C) Secret.z++;
D) Secret secret = new Secret(4);

Question 49

public class Secret
{
Private int x;
Private static int y;
Public static int count;
Public int z;
Public Secret()
{
X = 0;
Z = 1;
} public Secret(int a)
{
X = a;
} public Secret(int a, int b)
{
X = a;
Y = b;
} public String toString()
{
Return ("x = " + x + ", y = " + y + ",
Count = " + count);
} public static void incrementY()
{
Y++;
}
}How many constructors are present in the class definition in the accompanying figure?

A) zero
B) one
C) two
D) three

Question 50

public class Secret
{
Private int x;
Private static int y;
Public static int count;
Public int z;
Public Secret()
{
X = 0;
Z = 1;
} public Secret(int a)
{
X = a;
} public Secret(int a, int b)
{
X = a;
Y = b;
} public String toString()
{
Return ("x = " + x + ", y = " + y + ",
Count = " + count);
} public static void incrementY()
{
Y++;
}
}What might the heading of the copy constructor for the class in the accompanying figure look like?

A) public Secret(Secret s)
B) private copySecret()
C) Secret copySecret = new Secret()
D) public copySecret(int a, int b)