ch 2 oops

 

1️⃣ Encapsulation (C++)

🔹 Definition

Encapsulation means wrapping data (variables) and methods (functions) together into a single unit called a class, and restricting direct access to data.

👉 Achieved using:

• private

• protected

• public

🔹 Why Needed?

• Data security

• Prevents unauthorized access

• Controls modification

🔹 Example in C++

#include <iostream>
using namespace std;

class BankAccount {
private:
    double balance;   // Hidden data

public:
    void deposit(double amount) {
        balance += amount;
    }

    double getBalance() {
        return balance;
    }
};

int main() {
    BankAccount obj;
    obj.deposit(5000);
    cout << obj.getBalance();
}

✅ balance cannot be accessed directly.
This is data hiding + encapsulation.

---

2️⃣ Data Abstraction (C++)

🔹 Definition

Abstraction means hiding internal implementation details and showing only essential features.

👉 Real Example:
ATM machine — you press buttons, but don’t know internal logic.

🔹 Achieved by:

• Classes

• Access specifiers

• Abstract classes (using virtual functions)

🔹 Example

class Shape {
public:
    virtual void area() = 0;  // Pure virtual function
};

User only knows area() exists, not how it works internally.

---

3️⃣ Concept of Object

An Object is an instance of a class.

Every object has:

🔹 1. State

Represents data/attributes of object.

Example:

int speed;
string color;

🔹 2. Behavior

Functions that object performs.

Example:

void accelerate();
void brake();

🔹 3. Identity

Unique name/reference of object in memory.

Example:

Car c1, c2;

c1 and c2 are different identities.

---

Object Representation Diagram

        Object: Car c1
        -----------------
        State: color=Red
               speed=80
        -----------------
        Behavior:
               accelerate()
               brake()
        -----------------
        Identity:
               Memory Address

---

4️⃣ Classes

🔹 Definition

A Class is a blueprint or template for creating objects.

class Student {
public:
    int roll;
    string name;
};

---

5️⃣ Identifying Classes and Candidate Classes

When designing software:

Step 1: Identify Nouns from Problem Statement

Example:
Library Management System

Nouns:

• Book

• Student

• Librarian

• Issue

• Return

These are Candidate Classes.

Step 2: Filter Relevant Classes

Final Classes:

• Book

• Student

• Library

---

6️⃣ Attributes and Services

🔹 Attributes

Data members of class.

Example:

int roll;
string name;

🔹 Services

Functions provided by class.

Example:

void display();
void input();

---

7️⃣ Access Modifiers in C++

Modifier	Accessibility
private	Inside class only
protected	Inside class + derived class
public	Anywhere

Example

class Demo {
private:
    int a;

protected:
    int b;

public:
    int c;
};

---

8️⃣ Static Members of a Class

🔹 Static Data Member

Shared among all objects.

class Student {
public:
    static int count;
};

int Student::count = 0;

🔹 Static Function

static void showCount() {
    cout << count;
}

👉 Accessed using:

Student::showCount();

---

9️⃣ Instances

An Instance is another word for Object.

Student s1;  // Instance
Student s2;  // Another instance

Each instance has separate data.

---

🔟 Message Passing

Objects communicate by calling functions.

Example:

s1.display();

Here:

• s1 sends message to display() function.

---

1️⃣1️⃣ Construction of Objects (Constructor)

🔹 Definition

Special function with same name as class.
Used to initialize object.

🔹 Example

class Student {
public:
    Student() {
        cout << "Constructor Called";
    }
};

Types:

• Default Constructor

• Parameterized Constructor

• Copy Constructor

---

1️⃣2️⃣ Destruction of Objects (Destructor)

🔹 Definition

Special function with ~ symbol.
Called automatically when object is destroyed.

class Student {
public:
    ~Student() {
        cout << "Destructor Called";
    }
};

Used for:

• Memory cleanup

• File closing

• Resource releasing

---

🔥 Full C++ Example (All Concepts Together)

#include <iostream>
using namespace std;

class Student {
private:
    int roll;

public:
    static int count;

    Student(int r) {
        roll = r;
        count++;
        cout << "Constructor called\n";
    }

    void display() {
        cout << "Roll: " << roll << endl;
    }

    ~Student() {
        cout << "Destructor called\n";
    }
};

int Student::count = 0;

int main() {
    Student s1(101);
    Student s2(102);

    s1.display();
    s2.display();

    cout << "Total Students: " << Student::count;
}