1 What is encapsulation?
Containing and hiding information about an object, such as internal data structures and code. Encapsulation isolates the internal complexity of an object’s operation from the rest of the application. For example, a client component asking for net revenue from a business object need not know the data’s origin.
2 What is inheritance?
Inheritance allows one class to reuse the state and behavior of another class. The derived class inherits the properties and method implementations of the base class and extends it by overriding methods and adding additional properties and methods.
3 What is Polymorphism?
Polymorphism allows a client to treat different objects in the same way even if they were created from different classes and exhibit different behaviors.
You can use implementation inheritance to achieve polymorphism in languages such as C++ and Java.
Base class object’s pointer can invoke methods in derived class objects.
You can also achieve polymorphism in C++ by function overloading and operator overloading.
4 What is constructor or ctor?
Constructor creates an object and initializes it. It also creates vtable for virtual functions. It is different from other methods in a class.
5 What is destructor?
Destructor usually deletes any extra resources allocated by the object.
What is default constructor?
Constructor with no arguments or all the arguments has default values.
6 What is copy constructor?
Constructor which initializes the it’s object member variables ( by shallow copying) with another object of the same class. If you don’t implement one in your class then compiler implements one for you.
Boo Obj1(10); // calling Boo constructor
Boo Obj2(Obj1); // calling boo copy constructor
Boo Obj2 = Obj1;// calling boo copy constructor
When are copy constructors called?
Copy constructors are called in following cases:
a) when a function returns an object of that class by value
b) when the object of that class is passed by value as an argument to a function
c) when you construct an object based on another object of the same class
d) When compiler generates a temporary object
7 What is assignment operator?
Default assignment operator handles assigning one object to another of the same class. Member to member copy (shallow copy)
What are all the implicit member functions of the class? Or what are all the functions which compiler implements for us if we don’t define one.??
8 What is conversion constructor?
constructor with a single argument makes that constructor as conversion ctor and it can be used for type conversion.
Boo( int i );
Boo BooObject = 10 ; // assigning int 10 Boo object
9 What is conversion operator?
class can have a public method for specific data type conversions.
Boo(int i )
double i = BooObject; // assigning object to variable i of type double. now conversion operator gets called to assign the value.
10 What is diff between malloc()/free() and new/delete?
malloc allocates memory for object in heap but doesn’t invoke object’s constructor to initiallize the object.
new allocates memory and also invokes constructor to initialize the object.
malloc() and free() do not support object semantics
Does not construct and destruct objects
string * ptr = (string *)(malloc (sizeof(string)))
Are not safe
Does not calculate the size of the objects that it construct
Returns a pointer to void
int *p = (int *) (malloc(sizeof(int)));
int *p = new int;
Are not extensible
new and delete can be overloaded in a class
“delete” first calls the object’s termination routine (i.e. its destructor) and then releases the space the object occupied on the heap memory. If an array of objects was created using new, then delete must be told that it is dealing with an array by preceding the name with an empty :-
Int_t *my_ints = new Int_t;