Pillars of OOPs

Object-Oriented Programming (OOP) is built on four main pillars: Abstraction, Encapsulation, Inheritance, and Polymorphism. Each of these concepts plays a crucial role in creating modular, reusable, and maintainable code.

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1. Abstraction

Abstraction is the process of hiding the complex implementation details and showing only the essential features of an object. It allows developers to reduce complexity by providing a simplified interface.

Key Points

• Focuses on what an object does rather than how it does it.
• Achieved through abstract classes and interfaces.

Example of Abstraction

C++ Code

#include <iostream>
using namespace std;

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

class Circle : public Shape {
public:
    void draw() {
        cout << "Drawing Circle" << endl;
    }
};

int main() {
    Circle circle;
    circle.draw(); // Calls the draw method
    return 0;
}

Java Code

abstract class Shape {
    abstract void draw(); // Abstract method
}

class Circle extends Shape {
    void draw() {
        System.out.println("Drawing Circle");
    }
}

public class Main {
    public static void main(String[] args) {
        Circle circle = new Circle();
        circle.draw(); // Calls the draw method
    }
}

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2. Encapsulation

Encapsulation is the bundling of data (attributes) and methods (functions) that operate on the data into a single unit called a class. It restricts direct access to some of the object's components, which is a means of preventing unintended interference and misuse.

Key Points

• Protects an object's state by restricting access to its internal data.
• Achieved using access modifiers (private, protected, public).

Example of Encapsulation

C++ Code

#include <iostream>
using namespace std;

class BankAccount {
private:
    double balance; // Private data member

public:
    BankAccount() : balance(0) {} // Constructor

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

    void displayBalance() {
        cout << "Balance: " << balance << endl;
    }
};

int main() {
    BankAccount account;
    account.deposit(1000);
    account.displayBalance(); // Displays the balance
    return 0;
}

Java Code

class BankAccount {
    private double balance; // Private data member

    public BankAccount() {
        balance = 0; // Constructor
    }

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

    public void displayBalance() {
        System.out.println("Balance: " + balance);
    }
}

public class Main {
    public static void main(String[] args) {
        BankAccount account = new BankAccount();
        account.deposit(1000);
        account.displayBalance(); // Displays the balance
    }
}

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3. Inheritance

Inheritance is a mechanism that allows one class to inherit the properties and behaviors (methods) of another class. It promotes code reusability and establishes a hierarchical relationship between classes.

Key Points

• The class that inherits is called the derived class or child class, and the class being inherited from is called the base class or parent class.
• Supports "is-a" relationship.

Example of Inheritance

C++ Code

#include <iostream>
using namespace std;

class Animal {
public:
    void eat() {
        cout << "Eating..." << endl;
    }
};

class Dog : public Animal { // Dog inherits from Animal
public:
    void bark() {
        cout << "Woof!" << endl;
    }
};

int main() {
    Dog dog;
    dog.eat(); // Inherited method
    dog.bark(); // Dog's own method
    return 0;
}

Java Code

class Animal {
    void eat() {
        System.out.println("Eating...");
    }
}

class Dog extends Animal { // Dog inherits from Animal
    void bark() {
        System.out.println("Woof!");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.eat(); // Inherited method
        dog.bark(); // Dog's own method
    }
}

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4. Polymorphism

Polymorphism allows methods to do different things based on the object it is acting upon. It means "many forms" and can be classified into two types: Compile-time polymorphism and Runtime polymorphism.

4.1 Compile-time Polymorphism

Also known as method overloading, it occurs when multiple methods in the same class have the same name but different parameters.

Example of Compile-time Polymorphism

C++ Code

#include <iostream>
using namespace std;

class Math {
public:
    int add(int a, int b) {
        return a + b;
    }

    double add(double a, double b) {
        return a + b;
    }
};

int main() {
    Math math;
    cout << "Int Addition: " << math.add(5, 10) << endl; // Calls int version
    cout << "Double Addition: " << math.add(5.5, 10.5) << endl; // Calls double version
    return 0;
}

Java Code

class Math {
    int add(int a, int b) {
        return a + b;
    }

    double add(double a, double b) {
        return a + b;
    }
}

public class Main {
    public static void main(String[] args) {
        Math math = new Math();
        System.out.println("Int Addition: " + math.add(5, 10)); // Calls int version
        System.out.println("Double Addition: " + math.add(5.5, 10.5)); // Calls double version
    }
}

4.2 Runtime Polymorphism

Also known as method overriding, it occurs when a derived class provides a specific implementation of a method that is already defined in its base class. The decision about which method to call is made at runtime.

Example of Runtime Polymorphism

C++ Code

#include <iostream>
using namespace std;

class Animal {
public:
    virtual void sound() { // Virtual method
        cout << "Animal sound" << endl;
    }
};

class Dog : public Animal {
public:
    void sound() override { // Override method
        cout << "Woof!" << endl;
    }
};

int main() {
    Animal* animal = new Dog(); // Pointer to base class
    animal->sound(); // Calls Dog's sound method
    delete animal;
    return 0;
}

Java Code

class Animal {
    void sound() { // Base class method
        System.out.println("Animal sound");
    }
}

class Dog extends Animal {
    void sound() { // Override method
        System.out.println("Woof!");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal animal = new Dog(); // Reference to base class
        animal.sound(); // Calls Dog's sound method
    }
}

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Differences between Compile-time and Runtime Polymorphism

Feature	Compile-time Polymorphism	Runtime Polymorphism
Definition	Achieved through method overloading.	Achieved through method overriding.
Binding Time	Resolved during compilation.	Resolved during runtime.
Method Resolution	The compiler determines which method to call.	The JVM determines which method to call.
Performance	Generally faster due to early binding.	Slightly slower due to late binding.
Flexibility	Less flexible as the decision is made at compile time.	More flexible as the decision is made at runtime.
Example	Overloading methods with different parameters.	Overriding a method in a derived class.

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