Question: What is Abstraction?
Answer: The importance of abstraction is derived from its ability to hide irrelevant details and
from the use of names to reference objects. Abstraction is essential in the construction of
programs. It places the emphasis on what an object is or does rather than how it is
represented or how it works. Thus, it is the primary means of managing complexity in
large programs.
Question: What is a Class Diagram?
Answer: A class diagrams are widely used to describe the types of objects in a system and their
relationships. Class diagrams model class structure and contents using design elements
such as classes, packages and objects.
Question: What is Method Overriding?
Answer: Method overriding is a language feature that allows a subclass to override a specific
implementation of a method that is already provided by one of its super-classes. A
subclass can give its own definition of methods but need to have the same signature as
the method in its super-class. This means that when overriding a method the subclass's
method has to have the same name and parameter list as the super-class's overridden
method.
Question: What is Operator Overloading?
Answer: The operator overloading is a specific case of polymorphisms in which some or all of
operators like +, - or == are treated as polymorphic (multi) functions and as such have
different behaviors depending on the types of its arguments.
Question: What is Method Overloading?
Answer: The method overloading is the ability to define several methods (in same class) all with
the same name but different on the basis of i) number of parameters ii) types of
parameters.
Question: What is Polymorphisms?
Answer: Polymorphism is a generic term that means 'many shapes'. More precisely Polymorphism
means the ability to request that the same operations be performed by a wide range of
different types of things.
Question: What is Inheritance?
Answer: Ability of a new class to be created, from an existing class by extending it, is called
inheritance.
Question: What is a base class?
Answer: When inheritance is used to create a new class from another, the new class is called the
subclass or derived class, and the class from which it was derived is called the base class.
Question: What is a concrete class?
Answer: A concrete class is one that can be used to directly create, or instantiate objects, unlike an
abstract base class which can only be used as a base class for other classes which
eventually lead to concrete classes
Question: What are data members?
Answer: Objects are miniature programs, consisting of both code and data. The code consists of a
series of member functions. The data items are called data members.
Question: What is a constructor?
Answer: Objects are complete, miniature programs and, like any good programs, have well
defined initialization and termination phases. They have special routines (i.e. member
functions ) to look after this. The initialization routine is called the constructor, and C++
ensures that every object is properly initialized by calling its constructor. The designer of
the object can have more than one constructor, a situation called overloading and then the
compiler will select between them depending on exactly what arguments are passed to the
constructor function. However there must always be a default constructor, to be used
when no information is supplied.
Question: What is a destructor?
Answer: The termination routine is called the destructor, and C++ will provide a default if none is
supplied. If, during the lifetime of the object, it uses heap memory then the designer of
the object must provide a destructor function to release such memory to avoid a memory
leak.
Question: What is global variable?
Answer: Global variables can be accessed throughout a program. Another way to put this is to say
they have global scope.
Question: What is local variable?
Answer: Local variables can only be accessed within the function, or more specifically the
compound statement in which they are declared. Another way to put this is to say they
have local scope.
Question: What is a null pointer?
Answer: A null pointer is a pointer that is currently pointing to nothing. Often pointers are set to
zero to make them null pointers or tested against zero to see if they are null or not.
Question: What is a pointer?
Answer: A pointer is a variable that holds the address of another variable or object.
Question: What is meant by protected?
Answer: The protected keyword in the class statement means that the following members of the
class are not available to users of the objects of the class, but can be used by any subclass
that inherits from it, and consequently forms part of its implementation.
Question: What is OOP?
Answer: The object oriented programming is commonly known as OOP. Most of the languages
are developed using OOP concept. Object-oriented programming (OOP) is a
programming concept that uses "objects" to develop a system. An object hides the
implementation details and exposes only the functionalities and parameters it requires to
its client. Here also an object shares the same concept as that of a bike. While driving a
motor bike, we are unaware of its implementation details such as how it is developed,
internal working of gears etc.? We know only the functions or actions it can perform.
Question: What are the various elements of OOP?
Answer: Various elements of OOP are: Object Class Method Encapsulation Information Hiding
Inheritance Polymorphism
Question: What are the characteristics of Object Oriented programming language?
Answer: Some key features of the Object Oriented programming are: Emphasis on data rather than
procedure Programs are divided into entities known as objects Data Structures are
designed such that they characterize objects Functions that operate on data of an object
are tied together in data structures Data is hidden and cannot be accessed by external
functions Objects communicate with each other through functions New data and
functions can be easily added whenever necessary Follows bottom up design in program
design
Question: What are the basic Concepts used in the Object-Oriented Programming language?
Answer: Object Class Data Abstraction and Encapsulation Polymorphism Inheritance Message
passing Dynamic binding
Question: What Is An Object? (Object-Oriented Technology)
Answer: There are many definitions of an object, such as found in [Booch 91, p77]: "An object has
state, behavior, and identity; the structure and behavior of similar objects are defined in
their common class; the terms instance and object are interchangeable". This is a "classical
languages" definition, as defined in [Coplien 92, p280], where "classes play a central role
in the object model", since they do not in prototyping/delegation languages. "The term
object was first formally applied in the Simula language, and objects typically existed in
Simula programs to simulate some aspect of reality" [Booch 91, p77]. Other definitions
referenced by Booch include Smith and Tockey: "an object represents an individual,
identifiable item, unit, or entity, either real or abstract, with a well-defined role in the
problem domain." and [Cox 91]: "anything with a crisply defined boundary" (in context,
this is "outside the computer domain". A more conventional definition appears on pg 54).
Booch goes on to describe these definitions in depth. [Martin 92, p 241] defines: "An
"object" is anything to which a concept applies", and "A concept is an idea or notion we
share that applies to certain objects in our awareness". [Rumbaugh 91] defines: "We define
an object as a concept, abstraction or thing with crisp boundaries and meaning for the
problem at hand." [Shlaer 88, p 14] defines: "An object is an abstraction of a set of realworld
things such that:
Question: What Is Object Encapsulation (Or Protection)?
Answer: [Booch 91, p. 45] defines: "Encapsulation is the process of hiding all of the details of an
object that do not contribute to its essential characteristics." [Coad 91, 1.1.2] defines:
"Encapsulation (Information Hiding). A principle, used when developing an overall
program structure, that each component of a program should encapsulate or hide a single
design decision... The interface to each module is defined in such a way as to reveal as
little as possible about its inner workings. [Oxford, 1986]" Some languages permit
arbitrary access to objects and allow methods to be defined outside of a class as in
conventional programming. Simula and Object Pascal provide no protection for objects,
meaning instance variables may be accessed wherever visible. CLOS and Ada allow
methods to be defined outside of a class, providing functions and procedures. While both
CLOS and Ada have packages for encapsulation, CLOS's are optional while Ada's
methodology clearly specifies class-like encapsulation (Adts). However most objectoriented
languages provide a well defined interface to their objects thru classes. C++ has
a very general encapsulation/protection mechanism with public, private and protected
members. Public members (member data and member functions) may be accessed from
anywhere. A Stack's Push and Pop methods will be public. Private members are only
accessible from within a class. A Stack's representation, such as a list or array, will
usually be private. Protected members are accessible from within a class and also from
within subclasses (also called derived classes). A Stack's representation could be declared
protected allowing subclass access. C++ also allows a class to specify friends (other
(sub)classes and functions), that can access all members (its representation). Eiffel 3.0
allows exporting access to specific classes.
Question: What Is A Class?
Answer: A class is a general term denoting classification and also has a new meaning in objectoriented
methods. Within the OO context, a class is a specification of structure (instance
variables), behavior (methods), and inheritance (parents, or recursive structure and
behavior) for objects. As pointed out above, classes can also specify access permissions
for clients and derived classes, visibility and member lookup resolution. This is a featurebased
or intensional definition, emphasizing a class as a descriptor/constructor of objects
(as opposed to a collection of objects, as with the more classical extensional view, which
may begin the analysis process). Original Aristotlean classification defines a "class" as a
generalization of objects: [Booch 91, p93] "a group, set, or kind marked by common
attributes or a common attribute; a group division, distinction, or rating based on quality,
degree of competence, or condition".
Question: What Is A Meta-Class?
Answer: Meta-Class is a class' class. If a class is an object, then that object must have a class (in
classical OO anyway). Compilers provide an easy way to picture Meta-Classes. Classes
must be implemented in some way; perhaps with dictionaries for methods, instances, and
parents and methods to perform all the work of being a class. This can be declared in a
class named "Meta-Class". The Meta-Class can also provide services to application
programs, such as returning a set of all methods, instances or parents for review (or even
modification). [Booch 91, p 119] provides another example in Smalltalk with timers. In
Smalltalk, the situation is more complex
Question: What Is Inheritance?
Answer: Inheritance provides a natural classification for kinds of objects and allowsfor the
commonality of objects to be explicitly taken advantage of in modeling and constructing
object systems. Natural means we use concepts, classification, and generalization to
understand and deal with the complexities of the real world. See the example below using
computers. Inheritance is a relationship between classes where one class is the parent
base/superclass/ancestor/etc.) class of another. Inheritance provides programming by
extension (as opposed to programming by reinvention [LaLonde 90]) and can be used as
an is-a-kind-of (or is-a) relationship or for differential programming. Inheritance can also
double for assignment
Question: What Is The Difference Between Object-Based And Object-Oriented?
Answer: Object-Based Programming usually refers to objects without inheritance [Cardelli 85] and hence
without polymorphism, as in '83 Ada and Modula-2. These languages support abstract data
types (Adts) and not classes, which provide inheritance and polymorphism. Ada95 and Modula-
3; however, support both inheritance and polymorphism and are object-oriented. [Cardelli 85,
p481] state "that a language is object-oriented if and only if it satisfies the following
requirements: - It supports objects that are data abstractions with an interface of named
operations and a hidden local state. - Objects have an associated type. - Types may inherit
attributes from supertypes. object-oriented = data abstractions + object types + type inheritance
These definitions are also found in [Booch 91, Ch2 and Wegner 87]. [Coad 91] provides another
model: Object-Oriented = Classes and Objects + Inheritance + Communication with messages
Question No: 19 ( Marks: 2 )
What is difference between call by reference and call by value?
One application is to find duplicates in a list of numbers.
Let a given list be" 12 34 56 89 33 11 89
the first number in the list is placed in a node that is established as the root of a binary tree. Each number is
compared with the node in the root, if the number is larger, we search the right sub-tree else we search the left subtree.
If the sub-tree is empty, the number is not a duplicate and this will be added as a new node.
2. Binary trees can be used for sorting a given list such that, if we take the first number as root, the numbers less
than that number will be transfered to left sub-tree and the greater numbers to right sub-tree.
3. Binary trees are also used for developing the huffman codes.
Question No: 20 ( Marks: 3 )
What is the functionality of the following method of BST class
TreeNode* function(TreeNode* tree)
{
if( tree == NULL )
return NULL;
if( tree->getLeft() == NULL )
return tree; // this is it.
return function( tree->getLeft() );
}
Question No: 21 ( Marks: 3 )
a) Write a C++ statement that declares a valid reference of int i;
b) What is the benefit of reference and where can we use it?
In the last lecture we were discussing about reference variables, we saw three examples; call by
value, call by reference and call by pointer. We saw the use of stack when a function is called by
value, by reference or by pointer. The arguments passed to the function and local variables are
pushed on to the stack. There is one important point to note that in this course, we are using C/C++
but the usage of stack is similar in most of the computer languages like FORTRAN and Java . The
syntax we are using here is C++ specific, like we are sending a parameter by pointer using & sign. In
Java, the native data types like int, float are passed by value and the objects are passed by reference.
In FORTRAN, every parameter is passed by reference. In PASCAL, you can pass a parameter by
value or by reference like C++. You might have heard of ALGOL, this language had provided
another way of passing parameter ca
lled call by name. These kinds of topics are covered in subjects like
Question No: 22 ( Marks: 5 )
Determine what the following recursive “mystery” function computes when given a pointer to the root node
of a binary tree.
struct bt_s { int key; struct bt_s *left, *right; } bt_t;
int MFunc (bt_t *T) {
int N1, N2;
if (T == NULL) return -1;
N1 = MFunc(T->left);
N2 = MFunc(T->right);
return (N1 > N2 ? N1 : N2) + 1;
}
Answer: The importance of abstraction is derived from its ability to hide irrelevant details and
from the use of names to reference objects. Abstraction is essential in the construction of
programs. It places the emphasis on what an object is or does rather than how it is
represented or how it works. Thus, it is the primary means of managing complexity in
large programs.
Question: What is a Class Diagram?
Answer: A class diagrams are widely used to describe the types of objects in a system and their
relationships. Class diagrams model class structure and contents using design elements
such as classes, packages and objects.
Question: What is Method Overriding?
Answer: Method overriding is a language feature that allows a subclass to override a specific
implementation of a method that is already provided by one of its super-classes. A
subclass can give its own definition of methods but need to have the same signature as
the method in its super-class. This means that when overriding a method the subclass's
method has to have the same name and parameter list as the super-class's overridden
method.
Question: What is Operator Overloading?
Answer: The operator overloading is a specific case of polymorphisms in which some or all of
operators like +, - or == are treated as polymorphic (multi) functions and as such have
different behaviors depending on the types of its arguments.
Question: What is Method Overloading?
Answer: The method overloading is the ability to define several methods (in same class) all with
the same name but different on the basis of i) number of parameters ii) types of
parameters.
Question: What is Polymorphisms?
Answer: Polymorphism is a generic term that means 'many shapes'. More precisely Polymorphism
means the ability to request that the same operations be performed by a wide range of
different types of things.
Question: What is Inheritance?
Answer: Ability of a new class to be created, from an existing class by extending it, is called
inheritance.
Question: What is a base class?
Answer: When inheritance is used to create a new class from another, the new class is called the
subclass or derived class, and the class from which it was derived is called the base class.
Question: What is a concrete class?
Answer: A concrete class is one that can be used to directly create, or instantiate objects, unlike an
abstract base class which can only be used as a base class for other classes which
eventually lead to concrete classes
Question: What are data members?
Answer: Objects are miniature programs, consisting of both code and data. The code consists of a
series of member functions. The data items are called data members.
Question: What is a constructor?
Answer: Objects are complete, miniature programs and, like any good programs, have well
defined initialization and termination phases. They have special routines (i.e. member
functions ) to look after this. The initialization routine is called the constructor, and C++
ensures that every object is properly initialized by calling its constructor. The designer of
the object can have more than one constructor, a situation called overloading and then the
compiler will select between them depending on exactly what arguments are passed to the
constructor function. However there must always be a default constructor, to be used
when no information is supplied.
Question: What is a destructor?
Answer: The termination routine is called the destructor, and C++ will provide a default if none is
supplied. If, during the lifetime of the object, it uses heap memory then the designer of
the object must provide a destructor function to release such memory to avoid a memory
leak.
Question: What is global variable?
Answer: Global variables can be accessed throughout a program. Another way to put this is to say
they have global scope.
Question: What is local variable?
Answer: Local variables can only be accessed within the function, or more specifically the
compound statement in which they are declared. Another way to put this is to say they
have local scope.
Question: What is a null pointer?
Answer: A null pointer is a pointer that is currently pointing to nothing. Often pointers are set to
zero to make them null pointers or tested against zero to see if they are null or not.
Question: What is a pointer?
Answer: A pointer is a variable that holds the address of another variable or object.
Question: What is meant by protected?
Answer: The protected keyword in the class statement means that the following members of the
class are not available to users of the objects of the class, but can be used by any subclass
that inherits from it, and consequently forms part of its implementation.
Question: What is OOP?
Answer: The object oriented programming is commonly known as OOP. Most of the languages
are developed using OOP concept. Object-oriented programming (OOP) is a
programming concept that uses "objects" to develop a system. An object hides the
implementation details and exposes only the functionalities and parameters it requires to
its client. Here also an object shares the same concept as that of a bike. While driving a
motor bike, we are unaware of its implementation details such as how it is developed,
internal working of gears etc.? We know only the functions or actions it can perform.
Question: What are the various elements of OOP?
Answer: Various elements of OOP are: Object Class Method Encapsulation Information Hiding
Inheritance Polymorphism
Question: What are the characteristics of Object Oriented programming language?
Answer: Some key features of the Object Oriented programming are: Emphasis on data rather than
procedure Programs are divided into entities known as objects Data Structures are
designed such that they characterize objects Functions that operate on data of an object
are tied together in data structures Data is hidden and cannot be accessed by external
functions Objects communicate with each other through functions New data and
functions can be easily added whenever necessary Follows bottom up design in program
design
Question: What are the basic Concepts used in the Object-Oriented Programming language?
Answer: Object Class Data Abstraction and Encapsulation Polymorphism Inheritance Message
passing Dynamic binding
Question: What Is An Object? (Object-Oriented Technology)
Answer: There are many definitions of an object, such as found in [Booch 91, p77]: "An object has
state, behavior, and identity; the structure and behavior of similar objects are defined in
their common class; the terms instance and object are interchangeable". This is a "classical
languages" definition, as defined in [Coplien 92, p280], where "classes play a central role
in the object model", since they do not in prototyping/delegation languages. "The term
object was first formally applied in the Simula language, and objects typically existed in
Simula programs to simulate some aspect of reality" [Booch 91, p77]. Other definitions
referenced by Booch include Smith and Tockey: "an object represents an individual,
identifiable item, unit, or entity, either real or abstract, with a well-defined role in the
problem domain." and [Cox 91]: "anything with a crisply defined boundary" (in context,
this is "outside the computer domain". A more conventional definition appears on pg 54).
Booch goes on to describe these definitions in depth. [Martin 92, p 241] defines: "An
"object" is anything to which a concept applies", and "A concept is an idea or notion we
share that applies to certain objects in our awareness". [Rumbaugh 91] defines: "We define
an object as a concept, abstraction or thing with crisp boundaries and meaning for the
problem at hand." [Shlaer 88, p 14] defines: "An object is an abstraction of a set of realworld
things such that:
Question: What Is Object Encapsulation (Or Protection)?
Answer: [Booch 91, p. 45] defines: "Encapsulation is the process of hiding all of the details of an
object that do not contribute to its essential characteristics." [Coad 91, 1.1.2] defines:
"Encapsulation (Information Hiding). A principle, used when developing an overall
program structure, that each component of a program should encapsulate or hide a single
design decision... The interface to each module is defined in such a way as to reveal as
little as possible about its inner workings. [Oxford, 1986]" Some languages permit
arbitrary access to objects and allow methods to be defined outside of a class as in
conventional programming. Simula and Object Pascal provide no protection for objects,
meaning instance variables may be accessed wherever visible. CLOS and Ada allow
methods to be defined outside of a class, providing functions and procedures. While both
CLOS and Ada have packages for encapsulation, CLOS's are optional while Ada's
methodology clearly specifies class-like encapsulation (Adts). However most objectoriented
languages provide a well defined interface to their objects thru classes. C++ has
a very general encapsulation/protection mechanism with public, private and protected
members. Public members (member data and member functions) may be accessed from
anywhere. A Stack's Push and Pop methods will be public. Private members are only
accessible from within a class. A Stack's representation, such as a list or array, will
usually be private. Protected members are accessible from within a class and also from
within subclasses (also called derived classes). A Stack's representation could be declared
protected allowing subclass access. C++ also allows a class to specify friends (other
(sub)classes and functions), that can access all members (its representation). Eiffel 3.0
allows exporting access to specific classes.
Question: What Is A Class?
Answer: A class is a general term denoting classification and also has a new meaning in objectoriented
methods. Within the OO context, a class is a specification of structure (instance
variables), behavior (methods), and inheritance (parents, or recursive structure and
behavior) for objects. As pointed out above, classes can also specify access permissions
for clients and derived classes, visibility and member lookup resolution. This is a featurebased
or intensional definition, emphasizing a class as a descriptor/constructor of objects
(as opposed to a collection of objects, as with the more classical extensional view, which
may begin the analysis process). Original Aristotlean classification defines a "class" as a
generalization of objects: [Booch 91, p93] "a group, set, or kind marked by common
attributes or a common attribute; a group division, distinction, or rating based on quality,
degree of competence, or condition".
Question: What Is A Meta-Class?
Answer: Meta-Class is a class' class. If a class is an object, then that object must have a class (in
classical OO anyway). Compilers provide an easy way to picture Meta-Classes. Classes
must be implemented in some way; perhaps with dictionaries for methods, instances, and
parents and methods to perform all the work of being a class. This can be declared in a
class named "Meta-Class". The Meta-Class can also provide services to application
programs, such as returning a set of all methods, instances or parents for review (or even
modification). [Booch 91, p 119] provides another example in Smalltalk with timers. In
Smalltalk, the situation is more complex
Question: What Is Inheritance?
Answer: Inheritance provides a natural classification for kinds of objects and allowsfor the
commonality of objects to be explicitly taken advantage of in modeling and constructing
object systems. Natural means we use concepts, classification, and generalization to
understand and deal with the complexities of the real world. See the example below using
computers. Inheritance is a relationship between classes where one class is the parent
base/superclass/ancestor/etc.) class of another. Inheritance provides programming by
extension (as opposed to programming by reinvention [LaLonde 90]) and can be used as
an is-a-kind-of (or is-a) relationship or for differential programming. Inheritance can also
double for assignment
Question: What Is The Difference Between Object-Based And Object-Oriented?
Answer: Object-Based Programming usually refers to objects without inheritance [Cardelli 85] and hence
without polymorphism, as in '83 Ada and Modula-2. These languages support abstract data
types (Adts) and not classes, which provide inheritance and polymorphism. Ada95 and Modula-
3; however, support both inheritance and polymorphism and are object-oriented. [Cardelli 85,
p481] state "that a language is object-oriented if and only if it satisfies the following
requirements: - It supports objects that are data abstractions with an interface of named
operations and a hidden local state. - Objects have an associated type. - Types may inherit
attributes from supertypes. object-oriented = data abstractions + object types + type inheritance
These definitions are also found in [Booch 91, Ch2 and Wegner 87]. [Coad 91] provides another
model: Object-Oriented = Classes and Objects + Inheritance + Communication with messages
Question No: 19 ( Marks: 2 )
What is difference between call by reference and call by value?
One application is to find duplicates in a list of numbers.
Let a given list be" 12 34 56 89 33 11 89
the first number in the list is placed in a node that is established as the root of a binary tree. Each number is
compared with the node in the root, if the number is larger, we search the right sub-tree else we search the left subtree.
If the sub-tree is empty, the number is not a duplicate and this will be added as a new node.
2. Binary trees can be used for sorting a given list such that, if we take the first number as root, the numbers less
than that number will be transfered to left sub-tree and the greater numbers to right sub-tree.
3. Binary trees are also used for developing the huffman codes.
Question No: 20 ( Marks: 3 )
What is the functionality of the following method of BST class
TreeNode* function(TreeNode* tree)
{
if( tree == NULL )
return NULL;
if( tree->getLeft() == NULL )
return tree; // this is it.
return function( tree->getLeft() );
}
Question No: 21 ( Marks: 3 )
a) Write a C++ statement that declares a valid reference of int i;
b) What is the benefit of reference and where can we use it?
In the last lecture we were discussing about reference variables, we saw three examples; call by
value, call by reference and call by pointer. We saw the use of stack when a function is called by
value, by reference or by pointer. The arguments passed to the function and local variables are
pushed on to the stack. There is one important point to note that in this course, we are using C/C++
but the usage of stack is similar in most of the computer languages like FORTRAN and Java . The
syntax we are using here is C++ specific, like we are sending a parameter by pointer using & sign. In
Java, the native data types like int, float are passed by value and the objects are passed by reference.
In FORTRAN, every parameter is passed by reference. In PASCAL, you can pass a parameter by
value or by reference like C++. You might have heard of ALGOL, this language had provided
another way of passing parameter ca
lled call by name. These kinds of topics are covered in subjects like
Question No: 22 ( Marks: 5 )
Determine what the following recursive “mystery” function computes when given a pointer to the root node
of a binary tree.
struct bt_s { int key; struct bt_s *left, *right; } bt_t;
int MFunc (bt_t *T) {
int N1, N2;
if (T == NULL) return -1;
N1 = MFunc(T->left);
N2 = MFunc(T->right);
return (N1 > N2 ? N1 : N2) + 1;
}
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