Object-Oriented Programming (OOP) Basics

Object-Oriented Programming (OOP) is a programming paradigm that revolves around the concept of objects, which represent real-world entities, and their interactions. Java is a language that fully supports OOP principles. Here are the basic concepts of OOP in Java:

1. Classes and Objects

- Class: A class is a blueprint or template for creating objects. It defines the properties (attributes) and behaviors (methods) that objects of that class will have.

public class Car {
    // Attributes (fields)
    String color;
    int year;
    
    // Methods
    public void start() {
        System.out.println("Car started.");
    }
    
    public void stop() {
        System.out.println("Car stopped.");
    }
}

- Object: An object is an instance of a class. It represents a specific instance of the class, with its own unique set of attribute values.

Car myCar = new Car();
myCar.color = "Red";
myCar.year = 2022;
myCar.start();

2. Encapsulation

Encapsulation is the principle of bundling the data (attributes) and methods that operate on the data into a single unit (class). It hides the internal state of an object and only exposes necessary operations through methods, thus protecting the data from external interference.

public class Person {
    private String name;
    private int age;
    
    // Getter and setter methods
    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;
        } else {
            System.out.println("Invalid age.");
        }
    }
}

3. Inheritance

Inheritance is the mechanism by which one class (subclass or derived class) inherits the properties and behaviors of another class (superclass or base class). It promotes code reusability and allows you to create a hierarchy of classes.

public class Student extends Person {
    private int studentId;
    
    public int getStudentId() {
        return studentId;
    }
    
    public void setStudentId(int studentId) {
        this.studentId = studentId;
    }
}

4. Polymorphism

Polymorphism allows objects of different classes to be treated as objects of a common superclass. It enables methods to behave differently based on the object they are called on, leading to flexibility and extensibility in the code.

public class Animal {
    public void makeSound() {
        System.out.println("Animal makes a sound.");
    }
}

public class Dog extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Dog barks.");
    }
}

public class Cat extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Cat meows.");
    }
}

5. Abstraction

Abstraction is the process of hiding the implementation details and showing only the essential features of an object. It helps in reducing complexity and managing large codebases by focusing on what an object does rather than how it does it.

public interface Shape {
    double calculateArea();
}
public class Circle implements Shape {
    private double radius;
    
    public Circle(double radius) {
        this.radius = radius;
    }
    
    @Override
    public double calculateArea() {
        return Math.PI * radius * radius;
    }
}

Conclusion

Object-Oriented Programming is a powerful paradigm that promotes modularity, reusability, and maintainability in software development. Understanding these basic concepts of OOP in Java is crucial for writing efficient and structured code. As you delve deeper into Java programming, you'll encounter more advanced OOP concepts and design patterns that further enhance your skills in building robust and scalable applications.