Object-Oriented Programming in Java

Class Definition:

A class is a blueprint for creating objects. It defines the attributes (fields or data members) and methods (functions or behavior) that the objects of the class will have. Here's a basic example of a class:

public class Car {
    String make;
    String model;
    int year;

    public void displayInfo() {
        System.out.println("Make: " + make);
        System.out.println("Model: " + model);
        System.out.println("Year: " + year);
    }
}
  

Object Creation:

An object is an instance of a class. Once a class is defined, you can create multiple objects of that class. Here's how you can create an object of the Car class:

public class Main {
    public static void main(String[] args) {
        Car myCar = new Car();
        myCar.make = "Toyota";
        myCar.model = "Camry";
        myCar.year = 2022;
        myCar.displayInfo();
    }
}
  

Constructors:

A constructor is a special method that is called when an object is created. It initializes the object's state. If you don't explicitly define a constructor, Java provides a default constructor. Here's an example of a constructor:

public class Car {
    String make;
    String model;
    int year;

    public Car(String make, String model, int year) {
        this.make = make;
        this.model = model;
        this.year = year;
    }

    public void displayInfo() {
        System.out.println("Make: " + make);
        System.out.println("Model: " + model);
        System.out.println("Year: " + year);
    }
}
  

Encapsulation:

Encapsulation is the bundling of data and methods that operate on the data within a single unit (class). It hides the internal details of an object and exposes only what is necessary. In Java, you often use private access modifiers to achieve encapsulation.

Access Modifiers:

Access modifiers control the visibility of fields and methods. The main access modifiers in Java are:

• public: Accessible from anywhere.
• private: Accessible only within the same class.
• protected: Accessible within the same package or by subclasses.
• default (no modifier): Accessible within the same package.

Inheritance:

Inheritance is a mechanism where a class (subclass/derived class) inherits the properties and behaviors of another class (superclass/base class). It promotes code reuse and establishes a relationship between classes.

Example with Inheritance:

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

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

Polymorphism:

Polymorphism allows objects of different types to be treated as objects of a common type. It can be achieved through method overloading and method overriding.

Example with Polymorphism:

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

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

class Square extends Shape {
    @Override
    void draw() {
        System.out.println("Drawing a square");
    }
}
  

This is a high-level overview of object-oriented concepts in Java. OOP principles, including encapsulation, inheritance, and polymorphism, are fundamental to Java programming and contribute to creating modular, maintainable, and extensible code.