Object-Oriented Programming (OOP)

 Basics

 8.1  Introduction to OOP: 

• Object-Oriented Programming (OOP) is a programming paradigm that focuses on organizing code into objects that represent real-world entities.
• It provides a way to structure and modularize code, making it more manageable and reusable.

 8.2  Classes and Objects: 

• In OOP, a class is a blueprint for creating objects.
• It defines the properties (attributes) and behaviors (methods) that objects of that class will have.
• An object is an instance of a class.
• Here's an example:

Car.java File🖹

public class CarRunner {

	public static void main(String[] args) {
		// Creating objects
		Car car1 = new Car();
		Car car2 = new Car();

		// Accessing properties and invoking methods
		car1.color = "Red";
		car1.year = 2020;
		car1.startEngine(); // Output: "Engine started!"

		car2.color = "Blue";
		car2.year = 2018;
		car2.stopEngine(); // Output: "Engine stopped!"
	}
}

CarRunner.java File🖹

public class CarRunner {

	public static void main(String[] args) {
		// Creating objects
		Car car1 = new Car();
		Car car2 = new Car();

		// Accessing properties and invoking methods
		car1.color = "Red";
		car1.year = 2020;
		car1.startEngine(); // Output: "Engine started!"

		car2.color = "Blue";
		car2.year = 2018;
		car2.stopEngine(); // Output: "Engine stopped!"
	}
}

 8.3  Encapsulation and Data Hiding: 

• Encapsulation is the practice of hiding internal details of an object and providing public methods to interact with the object.
• It helps maintain data integrity and enhances code modularity. Access modifiers (e.g., private, public) control the visibility of class members.

public class Person {
	private String name;
	private int age;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		if (age > 0) {
			this.age = age;
		}
	}

	public static void main(String[] args) {
		Person person = new Person();
		person.setName("CM");
		person.setAge(-20); // Invalid age will be ignored

		System.out.println("Name: " + person.getName()); // Output: "Name: CM"
		System.out.println("Age: " + person.getAge()); // Output: "Age: 0"
	}
     }

 8.4  Inheritance: 

• Inheritance allows you to create a new class (subclass) based on an existing class (superclass).
• The subclass inherits the properties and behaviors of the superclass and can add its own unique features.

Animal.java File🖹

public class Animal {
	public void eat() {
		System.out.println("Animal is eating.");
	}

	public static void main(String[] args) {
		Dog dog = new Dog();
		dog.eat(); // Output: "Animal is eating."
		dog.bark(); // Output: "Dog is barking."
	}
}

Dog.java File🖹

public class Dog extends Animal {
	public void bark() {
		System.out.println("Dog is barking.");
	}
}

 8.5  Polymorphism: 

• Polymorphism allows objects of different classes to be treated as objects of a common superclass.
• It provides flexibility and extensibility in designing and working with objects.

Shape.java File🖹

public class Shape {
	public void draw() {
		System.out.println("Drawing a shape.");
	}

	public static void main(String[] args) {
		Shape shape1 = new Circle();
		Shape shape2 = new Rectangle();

		shape1.draw(); // Output: "Drawing a circle."
		shape2.draw(); // Output: "Drawing a rectangle."
	}
}

Circle.java File🖹

public class Circle extends Shape {
	@Override
	public void draw() {
		System.out.println("Drawing a circle.");
	}
}

Rectangle.java File🖹

public class Rectangle extends Shape {
	@Override
	public void draw() {
		System.out.println("Drawing a rectangle.");
	}
}

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