Deck 9: Inheritance

Question 1

For the questions below, use the following partial class definitions:
public class A1
{
public int x;
private int y;
protected int z;
...
}
public class A2 extends A1
{
protected int a;
private int b;
...
}
public class A3 extends A2
{
private int q;
...
}
Which of the following lists of instance data are accessible in class A2?

A) x, y, z, a, b
B) x, y, z, a
C) x, z, a, b
D) z, a, b
E) a, b

Answer 1

C
Explanation: C) Class A2 has access to all of its own instance data (a, b) and any instance data from A1 that were protected (z). Further, all classes, including A2, have access to A1's x since it is public, so x, z, a and b are accessible in A2.

Question 2

The instruction super( ); does which of the following?

A) calls the method super as defined in the current class
B) calls the method super as defined in the current class'parent class
C) calls the method super as defined in java.lang
D) calls the constructor as defined in the current class
E) calls the constructor as defined in the current class'parent class

Answer 2

E
Explanation: E) The instruction super represents an invocation of something in the current class'parent class. Since there is no message but merely super( ), it is an invocation of the parent class'constructor.

Question 3

If a programmer writes a class wanting it to be extended by another programmer, then this programmer must

A) change private methods and instance data to be protected
B) change public methods and instance data to be protected
C) change all methods to be protected
D) change the class to be protected
E) none of the above, the programmer does not have to change anything

Answer 3

A
Explanation: A) Protected items are accessible by any subclass of the class that defines them while private items cannot be accessed by any other class. Therefore, previously defined private items must now be protected. Previously defined public entities should remain public so that all other classes can still access those public entities. Previously defined private items should not be made public because this would allow all classes to access them rather than just child classes.

Question 4

For the questions below, consider the following class definition:
public class AClass
{
protected int x;
protected int y;
public AClass(int a, int b)
{
x = a;
y = b;
}
public int addEm( )
{
return x + y;
}
public void changeEm( )
{
x++;
y--;
}
public String toString( )
{
return "" + x + " " + y;
}
}
Two children of the same parent class are known as

A) aliases
B) relatives
C) clones
D) brothers
E) siblings

Question 5

Which of the following is an example of multiple inheritance?

A) A computer can be a mainframe or a PC
B) A PC can be a desktop or a laptop
C) A laptop is both a PC and a portable device
D) A portable device is a lightweight device
E) Macintosh and IBM PC are both types of PCs

Question 6

All classes in Java are directly or indirectly subclasses of the ________ class.

A) Wrapper
B) String
C) Reference
D) this
E) Object

Question 7

For the questions below, consider the following class definition:
public class AClass
{
protected int x;
protected int y;
public AClass(int a, int b)
{
x = a;
y = b;
}
public int addEm( )
{
return x + y;
}
public void changeEm( )
{
x++;
y--;
}
public String toString( )
{
return "" + x + " " + y;
}
}
Which of the following is True regarding Java classes?

A) All classes must have 1 parent but may have any number of children (derived or extended) classes
B) All classes must have 1 child (derived or extended) class but may have any number of parent classes
C) All classes must have 1 parent class and may have a single child (derived or extended) class
D) All classes can have any number (0 or more) of parent classes and any number of children (derived or extended) classes
E) All classes can have either 0 or 1 parent class and any number of children (derived or extended) classes

Question 8

For the questions below, consider the following class definition:
public class AClass
{
protected int x;
protected int y;
public AClass(int a, int b)
{
x = a;
y = b;
}
public int addEm( )
{
return x + y;
}
public void changeEm( )
{
x++;
y--;
}
public String toString( )
{
return "" + x + " " + y;
}
}
You want addEm to now add all three values and return the sum and changeEm to change x and y, but leave z alone. Which should you do?

A) Redefine addEm and changeEm without referencing super.addEm( ) or super.changeEm( )
B) Redefine addEm to return the value of z + super.addEm( ), but leave changeEm alone
C) Redefine changeEm to call super.changeEm( ) and then set z = x + y, but leave addEm alone
D) Redefine addEm to return the value of z + super.addEm( ) and redefine changeEm to call super.changeEm( ) and then set z = x + y
E) Redefine changeEm to call super.changeEm( ) without doing anything to z, and redefine addEm to return super.addEm( )

Question 9

For the questions below, use the following partial class definitions:
public class A1
{
public int x;
private int y;
protected int z;
...
}
public class A2 extends A1
{
protected int a;
private int b;
...
}
public class A3 extends A2
{
private int q;
...
}
Which of the following lists of instance data are accessible in A3?

A) x, y, z, a, b, q
B) a, b, q
C) a, q
D) x, z, a, q
E) x, a, q

Question 10

For the questions below, consider the following class definition:
public class AClass
{
protected int x;
protected int y;
public AClass(int a, int b)
{
x = a;
y = b;
}
public int addEm( )
{
return x + y;
}
public void changeEm( )
{
x++;
y--;
}
public String toString( )
{
return "" + x + " " + y;
}
}
Consider that you want to extend AClass to BClass. BClass will have a third int instance data, z. Which of the following would best define BClass'constructor?

A) public BClass(int a, int b, int c) {
Super(a, b, c);
}
B) public BClass(int a, int b, int c) {
X = a;
Y = b;
Z = c;
}
C) public BClass(int a, int b, int c) {
Z = c;
}
D) public BClass(int a, int b, int c) {
Super(a, b);
Z = c;
}
E) public BClass(int a, int b, int c) {
Super( );
}

Question 11

Which of the following is not a method of the Object class?

A) clone
B) compareTo
C) equals
D) toString
E) all of the above are methods of the Object class

Question 12

Inheritance through an extended (derived) class supports which of the following concepts?

A) interfaces
B) modulary
C) information hiding
D) code reuse
E) correctness

Question 13

Java does not support multiple inheritance, but some of the abilities of multiple inheritance are available by

A) importing classes
B) implementing interfaces
C) overriding parent class methods
D) creating aliases
E) using public rather than protected or private modifiers

Question 14

For the questions below, use the following partial class definitions:
public class A1
{
public int x;
private int y;
protected int z;
...
}
public class A2 extends A1
{
protected int a;
private int b;
...
}
public class A3 extends A2
{
private int q;
...
}
Which of the following is True regarding the use of instance data y of class A1?

A) It is accessible in A1, A2 and A3
B) It is accessible in A1 and A2
C) It is accessible only in A1
D) It is accessible only in A3
E) It is not accessible to any of the three classes

Question 15

For the questions below, consider the following class definition:
public class AClass
{
protected int x;
protected int y;
public AClass(int a, int b)
{
x = a;
y = b;
}
public int addEm( )
{
return x + y;
}
public void changeEm( )
{
x++;
y--;
}
public String toString( )
{
return "" + x + " " + y;
}
}
Which of the following would best redefine the toString method for BClass?

A) public String toString(int z) {
Return " " + x + " " + y + " " + z;
}
B) public String toString( ) {
Return super.toString( );
}
C) public String toString( ) {
Return super.toString( ) + " " + z;
}
D) public String toString( ) {
Return super.toString( ) + " " x + " " + y + " " + z;
}
E) public String toString( ) {
Return " " + x + " + y + " " + z;
}

Question 16

For the questions below, use the following partial class definitions:
public class A1
{
public int x;
private int y;
protected int z;
...
}
public class A2 extends A1
{
protected int a;
private int b;
...
}
public class A3 extends A2
{
private int q;
...
}
Which of the following is True with respect to A1, A2 and A3?

A) A1 is a subclass of A2 and A2 is a subclass of A3
B) A3 is a subclass of A2 and A2 is a subclass of A1
C) A1 and A2 are both subclasses of A3
D) A2 and A3 are both subclasses of A1
E) A1, A2 and A3 are all subclasses of the class A

Question 17

Aside from permitting inheritance, the visibility modifier protected is also used to

A) permit access to the protected item by any class defined in the same package
B) permit access to the protected item by any static class
C) permit access to the protected item by any parent class
D) ensure that the class can not throw a NullPointerException
E) define abstract elements of an interface

Question 18

For the questions below, consider the following class definition:
public class AClass
{
protected int x;
protected int y;
public AClass(int a, int b)
{
x = a;
y = b;
}
public int addEm( )
{
return x + y;
}
public void changeEm( )
{
x++;
y--;
}
public String toString( )
{
return "" + x + " " + y;
}
}
In order to determine the type that a polymorphic variable refers to, the decision is made

A) by the programmer at the time the program is written
B) by the compiler at compile time
C) by the operating system when the program is loaded into memory
D) by the Java run-time environment at run time
E) by the user at run time

Question 19

Abstract methods are used when defining

A) interface classes
B) derived classes
C) classes that have no constructor
D) arrays
E) classes that have no methods

Question 20

For the questions below, consider the following class definition:
public class AClass
{
protected int x;
protected int y;
public AClass(int a, int b)
{
x = a;
y = b;
}
public int addEm( )
{
return x + y;
}
public void changeEm( )
{
x++;
y--;
}
public String toString( )
{
return "" + x + " " + y;
}
}
A variable declared to be of one class can later reference an extended class of that class. This variable is known as

A) protected
B) derivable
C) cloneable
D) polymorphic
E) none of the above, a variable declared to be of one class can never reference any other type of class, even an extended class

Question 21

Using the reserved word, super, one can

A) access a parent class'constructor(s)
B) access a parent class'methods and instance data
C) access a child class'constructor(s)
D) access a child class'methods and instance data
E) none of the above

Question 22

If you instantiate an Abstract class, the class or object you wind up with

A) is also an Abstract class
B) is a normal class
C) is an Interface
D) is a reference to an Object
E) can't exist you cannot instantiate an Abstract class

Question 23

For the questions below, assume that Student, Employee and Retired are all extended classes of Person, and all four classes have different implementations of the method getMoney. Consider the following code where ... are the required parameters for the constructors:
Person p = new Person(...);
int m1 = p.getMoney( ); // assignment 1
p = new Student(...);
int m2 = p.getMoney( ); // assignment 2
if (m2 < 100000) p = new Employee(...);
else if (m1 > 50000) p = new Retired(...);
int m3 = p.getMoney( ); // assignment 3
Consider an applet that implements MouseListener. Assume that the applet has five instance data, int x1, x2, y1, y2, and boolean inside. The four int values represent the two end-points of a box (x1, y1 is the upper left hand point and x2, y2 is the lower right hand point). Which of the following properly defines code that will determine whenever the mouse button is clicked if the mouse is currently inside this box or not. If the mouse is inside the box, inside is set to True, otherwise it is set to false.

A) public void mouseMoved(MouseEvent me) {
If (me.getX( ) >= x1 && me.getX( ) <= x2 && me.getY( ) >= y1 && me.getY( ) <= y2)
Inside = True;
Else
Inside = false;
}
B) public void mousePressed(MouseEvent me) {
If (me.getX( ) >= x1 && me.getX( ) <= x2 && me.getY( ) >= y1 && me.getY( ) <= y2)
Inside = True;
Else
Inside = false;
}
C) public void mouseReleased(MouseEvent me) {
If (me.getX( ) >= x1 && me.getX( ) <= x2 && me.getY( ) >= y1 && me.getY( ) <= y2)
Inside = True;
Else
Inside = false;
}
D) public void mouseEntered(MouseEvent me) {
If (me.getX( ) >= x1 && me.getX( ) <= x2 && me.getY( ) >= y1 && me.getY( ) <= y2)
Inside = True;
Else
Inside = false;
}
E) Requires both of the following methods: public void mouseEntered(MouseEvent me)
{
Inside = True;
}
Public void mouseExited(MouseEvent me)
{
Inside = false;
}

Question 24

For the questions below, assume that Student, Employee and Retired are all extended classes of Person, and all four classes have different implementations of the method getMoney. Consider the following code where ... are the required parameters for the constructors:
Person p = new Person(...);
int m1 = p.getMoney( ); // assignment 1
p = new Student(...);
int m2 = p.getMoney( ); // assignment 2
if (m2 < 100000) p = new Employee(...);
else if (m1 > 50000) p = new Retired(...);
int m3 = p.getMoney( ); // assignment 3
The reference to getMoney( ) in assignment 3 is to the class

A) Person
B) Student
C) Employee
D) Retired
E) none of the above, this cannot be determined by examining the code

Question 25

As described in the Software Failure, the cause of the 2004 LA Air Traffic Control incident was

A) human error
B) the fact that the system had not been rebooted within 50 days
C) the fact that it takes just under 50 days for the countdown timer to count down four billion milliseconds and the subsystem shuts down when it reaches zero
D) there was no software patch to automatically reset the countdown timer without human intervention
E) all of the above

Question 26

Why shouldn't an abstract method be declared final?

A) There's nothing wrong with doing so
B) Abstract methods cannot be overridden and they must be if a concrete class ever is to be instantiated
C) So long as the Abstract method never actually is used in by any other method, there's no problem with doing this
D) So long as the Abstract method is declared in a Class (not an Interface), there's nothing wrong with doing this
E) None of the above

Question 27

For the next questions, consider the following class definition:
public class Q26_27
{
private int x;
public Q26_27(int newValue)
{
x = newValue;
}
}
Which of the following is True about the class Q26_27?

A) It has no parent class
B) Its parent class is Object
C) Its parent class is Java
D) It can not be extended
E) It has a default child called Object

Question 28

For the questions below, assume that Student, Employee and Retired are all extended classes of Person, and all four classes have different implementations of the method getMoney. Consider the following code where ... are the required parameters for the constructors:
Person p = new Person(...);
int m1 = p.getMoney( ); // assignment 1
p = new Student(...);
int m2 = p.getMoney( ); // assignment 2
if (m2 < 100000) p = new Employee(...);
else if (m1 > 50000) p = new Retired(...);
int m3 = p.getMoney( ); // assignment 3
The reference to getMoney( ) in assignment 1 is to the class

A) Person
B) Student
C) Employee
D) Retired
E) none of the above, this cannot be determined by examining the code

Question 29

What is the advantage of using an Adapter class?

A) It relieves the programmer from having to declare required methods with empty bodies
B) It is more efficient at run time
C) It relieves the programmer from having to shadow the required Interface variables
D) It allows a programmer to be more explicit about exactly which methods are being overridden and in what manner
E) none of the above

Question 30

Clicking the mouse button generates three mouse events, mousePressed, mouseClicked, and mouseReleased.

Question 31

Interface classes cannot be extended but classes that implement interfaces can be extended.

Question 32

A derived class has access to all of the methods of the parent class, but only the protected or public instance data of the parent class.

Question 33

Which of these is correct?

A) a base class is a parent class or super class
B) a base class is a child class or derived class
C) a child class is a super class of its parent
D) a parent class is a subclass of its child
E) none of the above

Question 34

For the questions below, assume that Student, Employee and Retired are all extended classes of Person, and all four classes have different implementations of the method getMoney. Consider the following code where ... are the required parameters for the constructors:
Person p = new Person(...);
int m1 = p.getMoney( ); // assignment 1
p = new Student(...);
int m2 = p.getMoney( ); // assignment 2
if (m2 < 100000) p = new Employee(...);
else if (m1 > 50000) p = new Retired(...);
int m3 = p.getMoney( ); // assignment 3
The reference to getMoney( ) in assignment 2 is to the class

A) Person
B) Student
C) Employee
D) Retired
E) none of the above, this cannot be determined by examining the code

Question 35

In order to implement the MouseListener interface, the programmer must define all of the following methods except for

A) mouseClicked
B) mouseDragged
C) mouseEntered
D) mouseReleased
E) all of the above must be defined to implement the MouseListener interface

Question 36

A mouse event is generated by

A) moving the mouse
B) clicking the mouse button
C) double clicking the mouse button
D) dragging the mouse
E) all of the above

Question 37

For the next questions, consider the following class definition:
public class Q26_27
{
private int x;
public Q26_27(int newValue)
{
x = newValue;
}
}
If q1 and q2 are objects of Q26_27, then q1.equals(q2)

A) is a syntax error since equals is not defined in the Q26_27 class
B) is True if q1 and q2 both store the same value of x
C) is True if q1 and q2 reference the same Q26_27 object
D) is never True
E) throws a NullPointerException

Question 38

A mouse event is a(n)

A) listener
B) object
C) interface
D) GUI component
E) all of the above

Question 39

JApplet is an extension of the Applet class and is found in the ________ library.

A) java.applet
B) java.awt
C) java.lang
D) java.japplet
E) javax.swing

Question 40

For the questions below, assume that Student, Employee and Retired are all extended classes of Person, and all four classes have different implementations of the method getMoney. Consider the following code where ... are the required parameters for the constructors:
Person p = new Person(...);
int m1 = p.getMoney( ); // assignment 1
p = new Student(...);
int m2 = p.getMoney( ); // assignment 2
if (m2 < 100000) p = new Employee(...);
else if (m1 > 50000) p = new Retired(...);
int m3 = p.getMoney( ); // assignment 3
The relationship between a parent class and a child class is referred to as a(n) ________ relationship.

A) has-a
B) is-a
C) was-a
D) instance-of
E) alias

Question 41

Consider the following class hierarchy and answer these questions.

If A, B, Y and Z all contain the same instance data d1, then d1 should be declared in X and inherited into Y, Z, A and B.

Question 42

An Applet implements MouseMotionListener and is 600x600 in size. Write a mouseMoved method so that if the mouse is moved into the upper left hand quadrant of the Applet, the entire applet turns blue, if the mouse is moved into the upper right hand quadrant of the Applet, the entire applet turns yellow, if the mouse is moved into the lower left hand quadrant of the Applet, the entire applet turns green, and if the mouse is moved into the lower right hand quadrant of the Applet, the entire applet turns red.

Question 43

If a class extends Applet and also implements MouseListener and MouseMotionListener, what methods must be declared in this class?

Question 44

Regarding the Software Failure: Mid-air collisions were avoided in the 2004 LA Air Traffic Control incident due to the on-board collision avoidance systems now found on commercial jets.

Question 45

For the questions below, assume that Poodle is a derived class of Dog and that Dog d = new Dog(...) and Poodle p = new Poodle(...) where the ... are the necessary parameters for the two classes.
The assignment statement p = d; is legal even though p is not a Dog.

Question 46

Consider the following class hierarchy and answer these questions.

Y is a derived class of Z.

Question 47

Java doesn't support multiple inheritance; but it does support the implementation of multiple Interfaces.

Question 48

For the questions below, assume that Poodle is a derived class of Dog and that Dog d = new Dog(...) and Poodle p = new Poodle(...) where the ... are the necessary parameters for the two classes.
The assignment statement d = p; is legal even though d is not a Poodle.

Question 49

Consider the following class hierarchy and answer these questions.

A is a derived class of X.

Question 50

You may use the super reserved word to access a parent class'private members.

Question 51

An Applet implements MouseMotionListener. Write the mouseMoved and paint methods for an applet that will display the location of the mouse as an (x, y) coordinate. The output should be given at location (10, 10) of the applet no matter where the mouse is.

Question 52

An Applet implements MouseMotionListener. Write the mouseMoved and paint methods for an applet that will display the location of the mouse as an (x, y) coordinate. The output should be given at the current mouse location.

Question 53

If class AParentClass has a protected instance data x, and AChildClass is a derived class of AParentClass, then AChildClass can access x but can not redefine x to be a different type.

Question 54

An applet implements MouseListener, and has int instance data x and y. These variables will be the (X, Y) coordinates of where the mouse is clicked. Every time the mouse is clicked, draw a 40x40 Oval centered around x and y. Write the mouseClicked and paint methods to draw the Oval every time the mouse is clicked.

Question 55

The protected visibility modifier provides the best possible encapsulation that permits inheritance.

Question 56

Assume a class Triangle has been defined. It has three instance data, Point p1, p2, p3. The class also has a constructor that receives the 3 Points and initializes p1, p2, and p3, a toString method that outputs the 3 Points, and a computeSurfaceArea method that calculates the surface area of the Triangle (as an int value). We want to extend this class to represent a 3-dimensional Pyramid, which consists of 4 Points. Since the Pyramid will consist of in essence, 4 triangles, computeSurfaceArea for the Pyramid will compute 4 * the surface area of the Triangle made up of 3 of those 4 Points. Write the Pyramid class to handle the difference(s) between a Pyramid and the previously defined Triangle. Assume the instance data of Triangle are protected and all methods are public. Also assume that the class Point has a toString method.

Question 57

Although classes can be inherited from one-another, even Abstract classes, interfaces cannot be inherited.

Question 58

Consider the following class hierarchy and answer these questions.

If classes C1 and C2 both implement an interface Cint, which has a method whichIsIt, and if C1 c = new C1( ); is performed at one point of the program, then a later instruction c.whichIsIt( ); will invoke the whichIsIt method defined in C1.

Question 59

Consider a class Plane and three subclasses, Glider, PropPlane and Jet. What instance data that should be declared in Plane and what instance data should be declared in one of the three subclasses. Come up with at least 2 instance data unique to each of the four classes given that all instance data of Plane will be inherited into the subclasses.

Question 60

The reserved word, extends, is used to denote a has-a relationship.

Question 61

Explain the difference between implementing an interface and a derived class.

Question 62

Explain the difference between using an imported class and extending a class.

Question 63

What is the advantage of extending an adapter class rather than implementing a listener interface?

Question 64

Why is it a contradiction for an abstract method to be modified as final or static?

Question 65

A motorcycle inherits properties from both a bicycle and a car. Java does not permit multiple inheritance. Assume that Bicycle and Car have both been declared. Explain how you might go about implementing a Motorcycle as a derived class.

Question 66

In what manners are Timer objects similar to and different from other GUI components?

Question 67

What instance data and methods might you define for SportsCar that are not part of Car?

Question 68

What methods inherited from Car should SportsCar override?

Question 69

Write the init and paint methods of an Applet and the methods needed to implement MouseMotionListener so that the applet can draw a point on the applet for every mouse position as the mouse is being moved on the screen. Use a 2-D array of ints to represent the X and Y coordinates of the mouse as it is being moved. For instance, point[0][0] and point[0][1] represent the X and Y coordinates of the mouse at its first position. The paint method will need to be called every time the mouse is moved and all points redrawn on the applet.

Question 70

Consider a class Name, which has four instance data (all Strings): first, middle, last and title. Even though Name inherits the equal method from Object, it would make more sense to override it. Why?

Question 71

Assume the class Student implements the Speaker interface from the textbook. Recall that this interface includes two abstract methods, speak( ) and announce(String str). A Student contains one instance data, String classRank. Write the Student class so that it implements Speaker as follows. The speak method will output "I am a newbie here" if the Student is a "Freshman", "I hate school" if the Student is either a "Sophomore" or a "Junior", or "I can not wait to graduate" if the student is a "Senior". The announce method will output "I am a Student, here is what I have to say" followed by the String parameter on a separate line. Finally, the classRank is initialized in the constructor. Only implement the constructor and the methods to implement the Speaker interface.