07 OOP

We did an entire course on this, so not much details have been written here. If any doubts, refer to Sem 3 > OOP notes

OOP¶

Object-Oriented Programming

• Classes are collection of properties/functions
• Objects are instances of that class
• Subclass, Superclass
• Method: Procedure body implementing operation
• Message: Procedure call; request to execute method

Purpose of OOP¶

• Data abstraction
• Data encapsulation
• Data hiding
• Polymorphism
• Inheritance is-a relationships

Classes¶

• Class declaration and definition
• Access specifiers
• Constructors
• Destructors (~Class())

Binary scope resolution operator¶

used for defining member function outside class

return_type ClassName::function_name()
{

}

// constructor
Line::Line() {
   ;
}

// destructor
Line::~Line() {
   ;
}

// regular functions
void Line::setLength() {
   ;
}

Inheritance¶

• Base/Parent/Super class
• Derived/Child/Sub class

Purpose¶

It allows a class to __ properties/functions of another class

• Re-use
• Extend
• Modify

class derived_class:access_specifier base_class {

};

class Rectangle: public Shape {
   public:
      int func() { 
        ;
      }
};

Access Specifiers¶

• Public
• Protected
• Private

Types¶

• Single
• Multiple
• Multi-Level
• Hierarchical

Polymorphism¶

Function Overloading¶

based on different argument list

Function overriding¶

Derived class function definition overrides parent class definition

Operator Overloading¶

Overloaded operators are functions with special names.

class className {
  public:
    returnType operator symbol (arguments) {
        ;
    } 
};

class Person {
  int age;
  Person()
  {
    age = 0;
  }
  void operator ++ () {
    ++age;
  }
};

void main() {
  Person p;

  ++p;
  // Calls ++ ()" that I defined
}

Following operators cannot be overloaded

• \(::\)
• \(.*\)
• \(?:\)

Virtual Function¶

Declared using virtual in base class

Member function of base class that is overriden by derived class

When you refer to a derived class object using a pointer or a reference to the base class, you can call a virtual function for that object and execute the derived class’s version of the function.

Used to achieve runtime polymorphism

Useful when you want a function to exist in the base class, but have no meaningful definition in the base class.

mutable¶

… is used for making data member of a object that is declared as a constant, to be changeable

Explanation¶

If we have an object that is declared as a constant, then by default, all the data members of this object now become constant. However, if you want one/more specific data members to be changeable, use mutable next to the data member in the class defintion.

class Student
{
  public:
    x = 0;
    mutable y = 0;
};

void main()
{
  const Student s;

  s.x = 10; // not possible
  s.y = 10; // possible due to mutable keyword
}

Order of invokation of nested objects¶

1. Nested object constructor
2. Outer object constructor
3. Outer object destructor
4. Nested object destructor

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