Question 1

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

Accepted Answer

Abstract methods are often used when defining interface classes, as interfaces define a set of methods but do not provide an implementation for them.

Question 2

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 cannot throw a NullPointException
E) define abstract elements of an interface

Accepted Answer

The protected visibility modifier allows access to the protected item by any class defined in the same package as well as any subclass, regardless of the package it is defined in. It does not permit access by any static class or parent class, nor does it have anything to do with throwing exceptions or defining abstract elements of an interface.

Question 3

Using the reserved word super, one can
A) access a parent class's constructor(s)
B) access a parent class's methods and instance data
C) access a child class's constructor(s)
D) access a child class's methods and instance data
E) Both A and B are correct

Accepted Answer

The reserved word "super" in Java is used to refer to the immediate parent class of the current class. It can be used to access a parent class's constructors (A) and also to access a parent class's methods and instance data (B), making both A and B correct. It is not used to access child class's constructors or methods and instance data, which eliminates options C and D.

Question 4

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

Accepted Answer

Java does not support multiple inheritance because it can lead to the diamond problem, where a subclass has multiple parent classes with conflicting implementations. Instead, Java uses interfaces to achieve some of the capabilities of multiple inheritance, such as inheriting behavior from multiple sources. By implementing interfaces, a class can define its own implementation of methods declared in the interface, making it possible to reuse code and extend the functionality of the class.

Question 5

Inheritance through an extended (derived) class supports which of the following concepts?
A) interfaces
B) modulary
C) information hiding
D) code reuse
E) correctness

Accepted Answer

Inheritance allows a class to inherit properties and methods from another base class, resulting in code reuse. Therefore, D is the correct choice. Interfaces, modularity, information hiding, and correctness are not directly related to inheritance through an extended class.

Question 6

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

Accepted Answer

Multiple inheritance occurs when a class or object inherits from multiple classes. In this case, a laptop can be seen as inheriting from both a PC class and a portable device class, making it an example of multiple inheritance. The other options do not involve multiple inheritance.

Question 7

Example Code Ch 09-5
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;
}
}
-Refer to Example Code Ch 09-5: 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;
}

Accepted Answer

Option A includes an additional parameter that is not in the original definition and would cause a compilation error. 
Option B simply returns the output of the superclass's toString method, and does not redefine it for the subclass. 
Option D is missing a plus sign between the quote and x, which would also cause a compilation error. 
Option E is missing quotes around the variables x and y, which would result in the output being " x + y " instead of the concatenated values of x and y. Option C, on the other hand, includes the addition of a new variable z to the output of the superclass's toString method, which is a valid and appropriate way to redefine the method in the subclass.

Question 8

Which of the following 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 these are correct

Accepted Answer

A base class is also known as a parent class or a super class because it serves as the basis for the derived classes or child classes that inherit its properties and methods. Option B is incorrect because a child class is not a base class, but rather a derived class. Option C and D are both incorrect because they confuse the parent-child relationship with the super-subclass relationship.

Question 9

If a programmer writes a class that he wants 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 the methods to be protected
D) change the class to be protected
E) None of these; the programmer doesn't have to change anything

Accepted Answer

Protected access allows subclasses to access private members of the superclass.

Question 10

Example Code Ch 09-5
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;
}
}
-Refer to Example Code Ch 09-5: You want addEm to now add all three values, 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().

Accepted Answer

The answer of Example Code Ch 09-5
Consider the following class...

Question 11

All classes in Java are directly or indirectly subclasses of the __________ class.
A) Wrapper
B) String
C) Reference
D) this
E) Object

Accepted Answer

All classes in Java are either directly or indirectly derived from the Object class, which is the root class of the Java class hierarchy.

Question 12

Example Code Ch 09-5
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;
}
}
-Refer to Example Code Ch 09-5: You want to extend AClass to BClass. BClass will have a third int instance data, z. Which of the following would best define BClass's 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();
}

Accepted Answer

Option D is the best choice because it calls the parent class constructor with the appropriate parameters for initializing x and y, and then initializes the new instance data z in BClass's constructor. Option A is close, but it has a typo where "super" is spelled with a capital 'S', it should be lowercase. Option B directly assigns the values to the instance variables, which bypasses the parent class's constructor and is generally discouraged. Option C only initializes z and doesn't set values for x and y. Option E calls the default parent class constructor, which doesn't have the required parameters to initialize x and y.

Question 13

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) you can't instantiate an abstract class

Accepted Answer

Abstract classes cannot be instantiated as they are incomplete classes which must be extended by subclasses before they can be used to create objects.

Question 14

Which of the following is true about Java classes?
A) All classes must have one parent but may have any number of children (derived or extended).
B) All classes must have one parent and may have a single child (derived or extended) but may have any number of parent classes.
C) All classes can have any number (zero or more) of parent classes and any number of children (derived or extended) classes.
D) All classes must have one parent and may have a single child (derived or extended) class.
E) All classes can have either zero or one parent class and any number of child (derived or extended) classes.

Accepted Answer

The answer of Which of the following is true about...

Question 15

Example Code Ch 09-6
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 ... indicates 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
-Refer to Example Code Ch 09-6: The reference to getMoney() in assignment 2 is to the class
A) Person
B) Student
C) Employee
D) Retired
E) This cannot be determined by examining the code

Accepted Answer

The reference to getMoney() in assignment 2 is to the class Student, as p is of type Student and hence calls the getMoney() method implemented in the Student class.

Question 16

Example Code Ch 09-6
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 ... indicates 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
-Refer to Example Code Ch 09-6: The reference to getMoney() in assignment 3 is to the class
A) Person
B) Student
C) Employee
D) Retired
E) This cannot be determined by examining the code

Accepted Answer

The class of the object referenced by 'p' at assignment 3 depends on the runtime values of 'm1' and 'm2', which are not provided in the code.

Question 17

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

Accepted Answer

The compareTo method is not a method of the Object class; it is typically found in classes that implement the Comparable interface.

Question 18

Example Code Ch 09-6
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 ... indicates 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
-Refer to Example Code Ch 09-6: The reference to getMoney() in assignment 1 is to the class
A) Person
B) Student
C) Employee
D) Retired
E) This cannot be determined by examining the code

Accepted Answer

Since p is of type Person in assignment 1, the getMoney() method called must be the one defined in the Person class.

Question 19

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

Accepted Answer

The relationship between a parent class and a child class is referred to as an "is-a" relationship, because the child class is a type of the parent class. This is a fundamental concept in object-oriented programming and is used to establish inheritance between classes. The other answer choices are not relevant to this relationship.

Question 20

Two children of the same parent class are known as
A) aliases
B) relatives
C) clones
D) brothers
E) siblings

Accepted Answer

Two children of the same parent class are known as siblings. A sibling is a term used in object-oriented programming to refer to a child class that shares its parent class with another child class. This term is commonly used in Java, C++, and other programming languages. Brothers and clones are not proper terms to describe children of the same parent class in programming. Aliases and relatives are not commonly used terms in programming to describe the relationship between child classes.

Quiz 9: Inheritance

Abstract methods are used when defining

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

Using the reserved word super, one can

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

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

Which of the following is an example of multiple inheritance?

Which of the following is correct?

If a programmer writes a class that he wants to be extended by another programmer, then this programmer must

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

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

Which of the following is true about Java classes?

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

The relationship between a parent class and a child class is referred to as a(n) __________ relationship.

Two children of the same parent class are known as