Category: Object Oriented Programming Objective Questions

Object Oriented Programming Questions Experienced people on “Execution of Constructor or Destructor”.

1. Which among the following best describes the constructors?
a) A function which is called whenever an object is referenced
b) A function which is called whenever an object is created to initialize the members
c) A function which is called whenever an object is assigned to copy the values
d) A function which is called whenever an object is to be given values for members
Answer: b
Clarification: The constructors are special type of functions which are called whenever an object is created. This is to initialize the data members of the class. The constructor allocates memory space for all the data members.

2. Which among the following best describes destructor?
a) A function which is called just before the objects are destroyed
b) A function which is called after each reference to the object
c) A function which is called after termination of the program
d) A function which is called before calling any member function
Answer: a
Clarification: The Destructors are special functions which are called just before an object is destroyed. This functions is responsible to free all the allocated resources to the object. Objects are destroyed whenever those go out of scope.

3. Which among the following represents correct constructor?
a) ()classname
b) ~classname()
c) –classname()
d) classname()
Answer: d
Clarification: The constructors must contain only the class name. The class name is followed by the blank parenthesis or we can have parameters if some values are to be passed.

4. Which among the following is correct syntax for the destructors?
a) classname()
b) ()classname
c) ~classname()
d) -classname()
Answer: c
Clarification: The destructor must have same name as that of the corresponding class. The class name should be preceded by the tilde symbol (~).

5. Which among the following is true?
a) First the constructor of parent classes are called in sequence of inheritance
b) First the constructor of child classes are called in the sequence of inheritance
c) First constructor called is of the object being created
d) Constructors are called randomly
Answer: a
Clarification: First the constructor of parent class are called. The order in which the parent class constructors are called is same in the sequence of inheritance used.

6. What is the sequence of destructors call?
a) Same order as that of the constructors call
b) Random order
c) According to the priority
d) Revere of the order of constructor call
Answer: d
Clarification: The destructors are called in the reverse order as that of the constructors being called. This is done to ensure that all the resources are released in sequence. That is, the derived class destructors will be called first.

7. The destructors _____________________
a) Can have maximum one argument
b) Can’t have any argument
c) Can have more than one argument
d) Can’t have more than 3 arguments
Answer: b
Clarification: The destructors doesn’t have any arguments. The destructors have to be called implicitly whenever an object goes out of scope. The user can’t pass argument to the implicit call.

8. Destructor calls ________________ (C++)
a) Are only implicit
b) Are only explicit
c) Can be implicit or explicit
d) Are made at end of program only
Answer: c
Clarification: The destructors are usually called implicitly whenever an object goes out of scope. The destructors can also be called explicitly if required. The call must be made, implicitly or explicitly.

9. Number of destructors called are ____________
a) Always equal to number of constructors called
b) Always less than the number of constructors called
c) Always greater than the number of constructors called
d) Always less than or equal to number of constructors
Answer: a
Clarification: Destructor will be called only to free the resources allocated for an object. The resources are allocated only the constructor for an object is called.

10. For explicit call _________________
a) The destructor must be private
b) The destructor must be public
c) The destructor must be protected
d) The destructor must be defined outside the class
Answer: b
Clarification: The destructor must be public for explicit calls. If it is made private or protected then it won’t be accessible outside the class. There is no restriction of definition the destructor outside the class.

11. If a class have 4 constructors then it must have 4 destructors also.
a) True
b) False
Answer: b
Clarification: Even if the class have 4 constructors, only one would be used. And only one destructor is allowed.

12. Which among the following is true for destructors?
a) Destructors can be overloaded
b) Destructors can be define more than one time
c) Destructors can’t be overloaded
d) Destructors are overloaded in derived classes
Answer: c
Clarification: The destructors can never be overloaded. The destructors doesn’t have arguments. And to get overloaded, they must have different signature. This is not possible if arguments are not allowed.

13. The constructor _____________
a) Have a return type
b) May have a return type
c) Of derived classes have return type
d) Doesn’t have a return type
Answer: d
Clarification: The constructors doesn’t have any return type. The constructors are intended to allocate the resources for the object. Memory spaces are to be finalized.

14. The destructors ____________
a) Have a return type
b) May have a return type
c) Of derived classes have return type
d) Doesn’t have a return type
Answer: d
Clarification: The destructors are intended to free the memory space. And all the resources that were allocated for the object. The return value is not supported since only memory has to be made free.

15. The destructor can be called before the constructor if required.
a) True
b) False
Answer: b
Clarification: The destructors can be called only after the constructor calls. It is not a mandatory rule but the deletion can only take place if there is something created using the constructor.

Object Oriented Programming for Experienced people,

Object Oriented Programming (OOPs) Multiple Choice Questions & Answers (MCQs) on “Template Class”.

1. A template class can have _____________
a) More than one generic data type
b) Only one generic data type
c) At most two data types
d) Only generic type of integers and not characters
Answer: a
Clarification: The template class can support more than one data type. The only thing is to add all the data types required in a list separated by comma within template specification.

2. Which among the following is the proper syntax for the template class?
a) template ;
b) Template ;
c) template T named(T x, T y){ }
d) Template T1 named(T1 x, T2 y){ }
Answer: c
Clarification: The syntax must start with keyword template, case sensitive. Then it should include the typename and a variable to denote it. Then whenever that variable is used, it replaces it with the data type needed.

3. Can default arguments be used with the template class?
a) Yes, in some special cases
b) Yes, always
c) No, it must satisfy some specific conditions first
d) No, it can’t be done
Answer: b
Clarification: The template class can use default arguments. This is used to specify the data type to be considered if it is not specified while passing to the generic class. The default type will be used.

4. What is the syntax to use explicit class specialization?
a) template class myClass<>{ }
b) template class myClass{ }
c) template <> class myClass<>{ }
d) template <> class myClass{ }
Answer: d
Clarification: The class specialization is creation of explicit specialization of a generic class. We have to use template<> constructor for this to work. It works in the same way as with explicit function specialization.

5. Which is the most significant feature that arises by using template classes?
a) Code readability
b) Ease in coding
c) Code reusability
d) Modularity in code
Answer: c
Clarification: The code reusability is the feature that becomes more powerful with the use of template classes. You can generate a single code that can be used in variety of programming situations.

6. A template class defines the form of a class _____________________ it will operate.
a) With full specification of the data on which
b) With full specification of the functions on which
c) Without full specification of the data on which
d) Without full specification of the functions on which
Answer: c
Clarification: The template classes can accept all types of data types. There is no need to specify the data on which the class has to operate. Hence it gives us flexibility to code without worrying about the type of data that might be used in the code.

7. What are the two specializations of I/O template classes in C++?
a) 16-bit character and wide characters
b) 8-bit character and wide characters
c) 32-bit character and locale characters
d) 64-bit characters and locale characters
Answer: b
Clarification: The I/O specialization is made with wide character and 8-bit characters. Wide characters are used to store the characters that might take more than 1 byte of space in memory or any size that is different from the one that the machine is using.

8. Can typeid() function be used with the object of generic classes?
a) Yes, only if default type is given
b) Yes, always
c) No, generic data can’t be determined
d) No, never possible
Answer: b
Clarification: The typeid() function can be used with the objects of generic classes. An instance of a template class will take the type of data that is being used with it. Hence when typeid() function is used, the data type would have already been defined and hence we can get desired result from typeid() function.

9. The _____________ class is a specialization of a more general template class.
a) String
b) Integer
c) Digit
d) Math
Answer: a
Clarification: The string class is more specialized. Since the string must be able to store any kind of data that is given to the string. Hence it needs maximum specialization.

10. How is function overloading different from template class?
a) Overloading is multiple function doing same operation, Template is multiple function doing different operations
b) Overloading is single function doing different operations, Template is multiple function doing different operations
c) Overloading is multiple function doing similar operation, Template is multiple function doing identical operations
d) Overloading is multiple function doing same operation, Template is same function doing different operations
Answer: c
Clarification: The function overloading is multiple functions with similar or different functionality but generic class functions perform the same task on given different types of data.

11. What if static members are declared inside template classes?
a) All instances will share the static variable
b) All instances will have their own static variable
c) All the instances will ignore the static variable
d) Program gives compile time error
Answer: b
Clarification: The generic class have a special case with static members. Each instance will have its own static member. The static members are not shared usually.

12. What is the output of following program?

template <typename T>
void test(const T&x) 
{
    static int count = 0;
    cout &lt;&lt; "x = " &lt;&lt; x &lt;&lt; " count = " &lt;&lt; count &lt;&lt; endl;
    ++count;
    return;
}
 
void main() 
{
    test<int> (2);
    test<int>(2);
    test<double>(2.2);
}

a)

x = 2 count = 0
x = 2.2 count = 0
x = 2.2 count = 0

b)

x = 2 count = 0
x = 2 count = 0
x = 2.2 count = 0

c)

x = 2 count = 0
x = 2 count = 1
x = 2.2 count = 0

d)

x = 2 count = 0
x = 2 count = 1
x = 2.2 count = 2

View Answer

Answer: c
Clarification: For each new type, the class will have separate instance. Here two instances will be created and hence counter for integer goes to 1. And for float value, the count remains 0 for the output.

13. If template class is defined, is it necessary to use different types of data for each call?
a) No, not necessary
b) No, but at least two types must be there
c) Yes, to make proper use of template
d) Yes, for code efficiency
Answer: a
Clarification: It is not necessary to use different type with each call to the generic function. Data may be of same type with each call but still the function works. We don’t consider other properties like efficiency with this concept because it is made generic to all data type, hence always works.

14. How many generic types can be given inside a single template class?
a) Only 1
b) Only 3
c) Only 7
d) As many as required
Answer: d
Clarification: There is no restriction on the number of types to be used for making the class generic. There can be any number of generic types with a single class. Hence giving flexibility to code with all the data types.

15. Template classes must have at least one static member.
a) True
b) False
Answer: b
Clarification: There is no mandatory condition to have static members inside template class. Not only template, it is not mandatory to have static members anywhere. We can use them as required in the code.

Object Oriented Programming Interview Questions freshers on “Overriding Member Functions”.

1. Which among the following best describes member function overriding?
a) Member functions having same name in base and derived classes
b) Member functions having same name in base class only
c) Member functions having same name in derived class only
d) Member functions having same name and different signature inside main function
Answer: a
Clarification: The member function which is defined in base class and again in the derived class, is overridden by the definition given in the derived class. This is because the preference is given more to the local members. When derived class object calls that function, definition from the derived class is used.

2. Which among the following is true?
a) Inheritance must not be using when overriding is used
b) Overriding can be implemented without using inheritance
c) Inheritance must be done, to use overriding are overridden
d) Inheritance is mandatory only if more than one functions
Answer: c
Clarification: The inheritance must be used in order to use function overriding. If inheritance is not used, the functions can only be overloaded. There must be a base class and a derived class to override the function of base class.

3. Which is the correct condition for function overriding?
a) The declaration must not be same in base and derived class
b) The declaration must be exactly the same in base and derived class
c) The declaration should have at least 1 same argument in declaration of base and derived class
d) The declaration should have at least 1 different argument in declaration of base and derived class
Answer: b
Clarification: For a function to be over ridden, the declaration must be exactly the same. There must not be any different syntax used. This will ensure that the function to be overridden is only the one intended from to be overridden from the derived class.

4. Exactly same declaration in base and derived class includes______________
a) Only same name
b) Only same return type and name
c) Only same return type and argument list
d) All the same return type, name and parameter list
Answer: d
Clarification: Declaration includes the whole prototype of the function. The return type name and the parameter list must be same in order to confirm that the function is same in derived and the base class. And hence can be overridden.

5. Which among function will be overridden from the function defined in derived class below:

class A
{
	int i;
	void show()
	{ 
		cout<<i; 
	}
	void print()
	{ 
		cout <<i; 
	}
};
class B
{
	int j;
	void show()
	{ 
		cout<<j; 
	}
};

a) show()
b) print()
c) show() and print()
d) Compile time error
Answer: a
Clarification: The declaration must be exactly same in the derived class and base class. The derived class have defined show() function with exactly same declaration. This then shows that the function in base class is being overridden if show() is called from the object of class B.

6. How to access the overridden method of base class from the derived class?
a) Using arrow operator
b) Using dot operator
c) Using scope resolution operator
d) Can’t be accessed once overridden
Answer: c
Clarification: Scope resolution operator :: can be used to access the base class method even if overridden. To access those, first base class name should be written followed by the scope resolution operator and then the method name.

7. The functions to be overridden _____________
a) Must be private in base class
b) Must not be private base class
c) Must be private in both derived and base class
d) Must not be private in both derived and base class
Answer: b
Clarification: If the function is private in the base class, derived class won’t be able to access it. When the derived class can’t access the function to be overridden then it won’t be able to override it with any definition.

8. Which language doesn’t support the method overriding implicitly?
a) C++
b) C#
c) Java
d) SmallTalk
Answer: b
Clarification: The feature of method overriding is not provided in C#. To override the methods, one must use override or virtual keywords explicitly. This is done to remove accidental changes in program and unintentional overriding.

9. In C# ____________________
a) Non – virtual or static methods can’t be overridden
b) Non – virtual and static methods only can be overridden
c) Overriding is not allowed
d) Overriding must be implemented using C++ code only
Answer: a
Clarification: The non-virtual and static methods can’t be overridden in C# language. The restriction is made from the language implicitly. Only the methods that are abstract, virtual or override can be overridden.

10. In Delphi ______________
a) Method overriding is done implicitly
b) Method overriding is not supported
c) Method overriding is done with directive override
d) Method overriding is done with the directive virtually
Answer: c
Clarification: This is possible but only if the method to be overridden is marked as dynamic or virtual. It is inbuilt restriction of programming language. This is done to reduce the accidental or unintentional overriding.

11. What should be used to call the base class method from the derived class if function overriding is used in Java?
a) Keyword super
b) Scope resolution
c) Dot operator
d) Function name in parenthesis
Answer: a
Clarification: The keyword super must be used to access base class members. Even when overriding is used, super must be used with the dot operator. The overriding is possible.

12. In Kotlin, the function to be overridden must be ______________
a) Private
b) Open
c) Closed
d) Abstract
Answer: b
Clarification: The function to be overridden must be open. This is a condition in Kotlin for any function to be overridden. This avoids accidental overriding.

13. Abstract functions of a base class _________________
a) Are overridden by the definition in same class
b) Are overridden by the definition in parent class
c) Are not overridden generally
d) Are overridden by the definition in derived class
Answer: d
Clarification: The functions declared to be abstract in base class are redefined in derived classes. That is, the functions are overridden by the definitions given in the derived classes. This must be done to give at least one definition to each undefined function.

14. If virtual functions are defined in the base class then _______________
a) It is not necessary for derived classes to override those functions
b) It is necessary for derived classes to override those functions
c) Those functions can never be derived
d) Those functions must be overridden by all the derived classes
Answer: a
Clarification: The derived classes doesn’t have to redefine and override the base class functions. If one definition is already given it is not mandatory for any derived class to override those functions. The base class definition will be used.

15. Which feature of OOP is exhibited by the function overriding?
a) Inheritance
b) Abstraction
c) Polymorphism
d) Encapsulation
Answer: c
Clarification: The polymorphism feature is exhibited by function overriding. Polymorphism is the feature which basically defines that same named functions can have more than one functionalities.

Object Oriented Programming for Interviews,

Object Oriented Programming (OOPs) Multiple Choice Questions & Answers (MCQs) on “Downcasting”.

1. What is downcasting?
a) Casting subtype to supertype
b) Casting supertype to subtype
c) Casting subtype to supertype and vice versa
d) Casting anytype to any other type
Answer: b
Clarification: The downcasting concept includes only the casting of supertypes to the sub types. This casting is generally done explicitly. Larger size types are made to fit into small size types explicitly.

2. Which among the following is a mandatory condition for downcasting?
a) It must not be done explicitly
b) It must be done implicitly
c) It must be done explicitly
d) It can’t be done explicitly
Answer: c
Clarification: The downcasting of any object must be done explicitly. This is because the compilers don’t support the implicit conversion of a supertype to subtype.

3. Downcasting is _______________________
a) Always safe
b) Never safe
c) Safe sometimes
d) Safe, depending on code
Answer: b
Clarification: The downcasting concept is made for exception cases. When there is a need to represent an entity in the form which is not suitable for it. Representing a base type in derived type is not right but can be done for special cases.

4. Downcasting ____________________
a) Can result in unexpected results
b) Can’t result in unexpected result
c) Can result only in out of memory error
d) Can’t result in any error
Answer: a
Clarification: The result of downcasting can be unexpected. This is because downcasting is done on the objects into the objects which doesn’t contain any information of data in lateral object.

5. What should be used for safe downcast?
a) Static cast
b) Dynamic cast
c) Manual cast
d) Implicit cast
Answer: b
Clarification: The dynamic cast can be done using the operator dynamic_cast. This converts one type to another type in a safe way.

6. What does dynamic_cast return after successful type casting?
a) Address of object which is converted
b) Address of object that is used for conversion
c) Address of object that is mentioned in the syntax
d) Doesn’t return any address
Answer: a
Clarification: The address of the object which is converted is returned by the dynamic_cast operator. This is done to safely convert the subtype to supertype. This ensures the proper assignment and conversion from one type to another.

7. If dynamic_cast fails, which value is returned?
a) void
b) null
c) void pointer
d) null pointer
Answer: d
Clarification: The null pointer is returned by the dynamic_cast, if it fails. The conversion sometimes fails because of too complex type conversion. The conversion may also fail due to memory or some related issues.

8. Which is the proper syntax of dynamic_cast?
a) dynamic_cast(object)
b) dynamic_cast new (object)
c) dynamic_cast(object)
d) dynamic_cast(object)
View Answer

Answer: c
Clarification: The dynamic_cast is the name of the operator, which is followed by the new type in which the object have to be converted. Then the object name is given. This object name is then used after the type conversion.

9. Which is the exception handler for the exceptions of downcasting?
a) CastException
b) ClassCastingExeption
c) ClassCasting
d) ClassCastException
Answer: d
Clarification: The exception handler for the exceptions produced during the downcasting exception. This handler can be called during runtime to handle any exception thrown.

10. How to prevent the ClassCastExceptions?
a) By using instanceof
b) By using is-a check
c) By using arrow operator with check function
d) By checking type of conversion
Answer: a
Clarification: The instanceof operator can be used to check the compatibility of the conversion. This has to be done to check whether the casting would be safe or not.

11. Java supports direct downcasting.
a) True
b) False
Answer: b
Clarification: The downcasting is not possible in java directly. This has to be done explicitly. The downcasting is not safe but can be checked for safe casting using instanceof function.

12. Which way the downcasting is possible with respect to inheritance?
a) Upward the inheritance order
b) Downward the inheritance order
c) Either upward or downward the inheritance order
d) Order of inheritance doesn’t matter
Answer: b
Clarification: The downcasting is always downward the inheritance order. Since the base class object have to be casted into derived class type. This is a basic definition of downcasting.

13. What happens when downcasting is done but not explicitly defined in syntax?
a) Compile time error
b) Runtime error
c) Code write time error
d) Conversion error
Answer: a
Clarification: The implicit downcasting is not possible. If tried, the compiler produces an error. Since the compiler doesn’t allow coasting to a type that is not compatible.

14. When is the downcasting used?
a) To separate inherited class from base class
b) To write a more complex code
c) To compare two objects
d) To disable one class in inheritance
Answer: c
Clarification: The downcasting can be used whenever there is a need to compare one object to another. Equals() function can be used to compare whether the objects were of same age. We can use getClass() function too.

15. Why is downcasting possible in any language?
a) Because inheritance follows has-a relationship
b) Because inheritance follows is-a relationship
c) Because inheritance doesn’t follow any relationship
d) Because inheritance is not involved in casting
Answer: b
Clarification: The downcasting is possible because the classes in inheritance follow is-a relationship. Hence the derived class is a base class. Which in turn make the downcasting possible.

Object Oriented Programming (OOPs) Multiple Choice Questions & Answers (MCQs) on ” Destructors”.

1. Which among the following describes a destructor?
a) A special function that is called to free the resources, acquired by the object
b) A special function that is called to delete the class
c) A special function that is called anytime to delete an object
d) A special function that is called to delete all the objects of a class
Answer: a
Clarification: It is used to free the resources that the object might had used in its lifespan. The destructors are called implicitly whenever an object’s life ends.

2. When a destructor is called?
a) After the end of object life
b) Anytime in between object’s lifespan
c) At end of whole program
d) Just before the end of object life
Answer: d
Clarification: The destructor is called just before the object go out of scope or just before its life ends. This is done to ensure that all the resources reserved for the object are used and at last, are made free for others.

3. Which among the following is correct for abstract class destructors?
a) It doesn’t have destructors
b) It has destructors
c) It may or may not have destructors
d) It contains an implicit destructor
Answer: a
Clarification: It doesn’t have destructors. Since an abstract class don’t have constructors, and hence can’t have instances. Having this case, the abstract classes don’t have destructors too, because that would be of no use here.

4. If in multiple inheritance, class C inherits class B, and Class B inherits class A. In which sequence are their destructors called if an object of class C was declared?
a) ~C() then ~B() then ~A()
b) ~B() then ~C() then ~A()
c) ~A() then ~B() then ~C()
d) ~C() then ~A() then ~B()
Answer: a
Clarification: The destructors are always called in the reverse order of how the constructors were called. Here class A constructor would have been created first if Class C object is declared. Hence class A destructor is called at last.

5. Choose the correct sequence of destructors being called for the following code.

class A{   };
class B{   };
class C: public A, public B{   };

a) ~A(), ~B(), ~C()
b) ~B(), ~C(), ~A()
c) ~A(), ~C(), ~B()
d) ~C(), ~B(), ~A()
Answer: d
Clarification: In multiple inheritance, the constructors are called in the sequence of how they are written in inheritance sequence. And the destructors will be called in the reverse order. This can be cross verified just by printing a message from each destructor defined in classes.

6. When is the destructor of a global object called?
a) Just before end of program
b) Just after end of program
c) With the end of program
d) Anytime when object is not needed
Answer: a
Clarification: This is because the lifespan of global object is from start of the program, till the end of the program. And hence program end is the end of global object too. Just before the end of program, the destructor will be called to free the acquired resources by the objects.

7. How the constructors and destructors can be differentiated?
a) Destructor have a return type but constructor doesn’t
b) Destructors can’t be defined by the programmer, but constructors can be defined
c) Destructors are preceded with a tilde (~) symbol, and constructor doesn’t
d) Destructors are same as constructors in syntax
Answer: c
Clarification: The destructors are preceded with the tilde (~) symbol. The name is same as that of the class. These also doesn’t have any return type.

8. Destructors doesn’t accept parameters.
a) True
b) False
Answer: a
Clarification: The destructors doesn’t accept the arguments. Those are just used to free up the resources.

9. Destructors can be ________
a) Abstract type
b) Virtual
c) Void
d) Any type depending on situation
Answer: b
Clarification: The destructors can be virtual. It is actually advised to keep the destructors virtual always. This is done to suppress the problems that may arise if inheritance is involved.

10. Global destructors execute in ___________ order after main function is terminated.
a) Sequential
b) Random
c) Reverse
d) Depending on priority
Answer: c
Clarification: The destructors are always called in reverse order no matter which destructor it is. This is done to ensure that all the resources are able to get free. And no resource is kept busy.

11. When is it advised to have user defined destructor?
a) When class contains some pointer to memory allocated in class
b) When a class contains static variables
c) When a class contains static functions
d) When a class is inheriting another class only
Answer: a
Clarification: This is always advised to have user defined destructor when pointers are involved in class. This is usually done to ensure that the memory, that was allocated dynamically, gets free after use and doesn’t cause memory leak.

12. Which among the following is correct for the destructors concept?
a) Destructors can be overloaded
b) Destructors can have only one parameter at maximum
c) Destructors are always called after object goes out of scope
d) There can be only one destructor in a class
Answer: d
Clarification: This is so because the destructors can’t be overloaded. And the destructor must have the same name as that of class with a tilde symbol preceding the name of the destructor. Hence there can be only one destructor in a class. Since more than one function with same name and signature can’t be present in same scope.

13. Which class destructor will be called first, when following code go out of scope?

class A{  };
class B{  };
class C: public B{  };
A a;
B b;
C c;

a) ~A()
b) ~B()
c) ~C()
d) ~B() and ~C()
Answer: c
Clarification: The constructor that would have created at last, its destructor will be called first when the code goes out of scope. This will help the program to manage the resources more efficiently.

14. When an object is passed to a function, its copy is made in the function and then ______________
a) The destructor of the copy is called when function is returned
b) The destructor is never called in this case
c) The destructor is called but it is always implicit
d) The destructor must be user defined
Answer: a
Clarification: When an object is passed to a function, its copy is made in the function. This copy acts as a real object till the function is live. When the function is returned, the copy’s destructor is called to free the resources held by it.

15. What happens when an object is passed by reference?
a) Destructor is not called
b) Destructor is called at end of function
c) Destructor is called when function is out of scope
d) Destructor is called when called explicitly
Answer: a
Clarification: The destructor is never called in this situation. The concept is that when an object is passed by reference to the function, the constructor is not called, but only the main object will be used. Hence no destructor will be called at end of function.

Object Oriented Programming (OOPs) Multiple Choice Questions & Answers (MCQs) on “Base Class”.

1. Which is most appropriate definition of a base class?
a) It is parent of any of its derived class
b) It is child of one of the parent class
c) It is most basic class of whole program
d) It is class with maximum number of members
Answer: a
Clarification: A class which is parent of another class, or from which other classes can be derived, is known as a base class. It is mandatory that a class must have at least one derived class to be called as a base class.

2. A base class is also known as _____________ class.
a) Basic
b) Inherited
c) Super
d) Sub
Answer: c
Clarification: A class which is being derived by other classes, is called as super class. This concept is clearly used in java as we call the functions of a base class by using the keyword super as required.

3. An abstract class is always a __________ class.
a) Base
b) Derived
c) Template
d) Nested
Answer: a
Clarification: Every abstract class is a base class. It must be so, because the functions which are not defined inside the abstract class, must be defined in the derived classes. Hence it becomes a base class.

4. How many base classes can a single class inherit in java?
a) 1
b) 2
c) 3
d) As many as required
Answer: a
Clarification: In java, multiple inheritance is not supported, which leads to the fact that a class can have only 1 parent class if inheritance is used. Only if interfaces are used then the class can implement more than one base class.

5. How to make a derived class a base class?
a) Change name of the class
b) Use keyword base
c) Make a class derive from it
d) Can’t be done
Answer: c
Clarification: Making another class derive from it will make that class as base class. It is not necessary that we have to write different code for it. If at least one class derives that class, it becomes the base class for the new class.

6. If a base class is being derived by two other classes, which inheritance will that be called?
a) Single
b) Multiple
c) Multi-level
d) Hierarchical
Answer: d
Clarification: When more than one classes are being derived from a single parent class, the inheritance is known as hierarchical inheritance. This is usually useful when the base class is higher abstraction of its derived classes.

7. Which among the following must be in a base class?
a) Data members
b) Member functions
c) Access specifiers
d) Nothing
Answer: d
Clarification: Even a class that doesn’t have any members can be a base class. It is not mandatory to have any member or attribute in base class.

8. Which type of members can’t be accessed in derived classes of a base class?
a) Protected
b) Private
c) Public
d) All can be accessed
Answer: b
Clarification: The private members can be accessed only inside the base class. If the class is derived by other classes. Those members will not be accessible. This concept of OOP is made to make the members more secure.

9. If a class is enclosing more than one class, than it can be called as base class of those classes.
a) True
b) False
Answer: b
Clarification: When a class have more than one nested classes, it is known as enclosing class. It can’t be called as parent or base class since there is no inheritance involved.

10. Base class have ________________ of abstraction.
a) Higher degree
b) Lower degree
c) Intermediate
d) Minimum degree
Answer: b
Clarification: A base class will have lesser information as compared to those of derived classes. Since derived classes inherit the base class properties and then add on their own features, they elaborate more hence have lower degree of abstraction.

11. Always the base class constructors are called ___________ constructor of derived class.
a) Before
b) After
c) Along
d) According to priority of
Answer: a
Clarification: When the base class object is created, its constructor will be called for sure. But if a derived class constructor is called, first base class constructor is called and then derived class constructor is taken into consideration.

12. Can we call methods of base class using the constructor of the derived class?
a) Yes, always
b) Yes, but not always
c) No, never
d) No, but we can call in some cases
Answer: a
Clarification: If the function is defined in the base class, it can always be called from the constructor of its derived class. Since the constructors are not private, they can be accessed in derived class even if those are protected.

13. If a base class is inherited from another class and then one class derives it, which inheritance is shown?
a) Multiple
b) Single
c) Hierarchical
d) Multi-level
Answer: d
Clarification: If a base class is inherited from another class, single inheritance is shown. But when one more class inherits the derived class, this becomes a multi-level inheritance.

14. How many base classes can a single derived class have in C++?
a) 1
b) 2
c) 3
d) As many as required
Answer: d
Clarification: This is because C++ allows multiple inheritance. A derived class can have more than one base class and hence can derive all of their features.

15. If a base class is added with a few new members, its subclass must also be modified.
a) True
b) False
Answer: b
Clarification: The base class can be added with new members without affecting the subclasses. This is because the subclasses may get some more features inherited but it won’t use them. But the base class will be able to use the new members as would be required.