Class

Welcome to the realm of Object Oriented Programming(2nd Chapter)

Today we are going to learn about classes and objects.Let's talk about classes.

Class:

In Object-Oriented Programming (OOP), a class is like a blueprint or template for creating objects (things that represent real-world entities). It defines the structure and behaviours that the objects created from it will have.Actually a class makes a new data type. For example, if we create a class named Student,then Student is one kind of user defined data type.We can assign different types of characteristics (built-in data types indeed).For example:

class Student
{
   String Name;
   int age;
   float CGPA;
 }

Besides we can also create methods(functions) inside the class.For example: we are willing to show the characteristics of the student.So,we need to write a funciton(method) for it.

 class Student
{
   String Name;
   int age;
   float CGPA;
    public void DisplayInfo()
   {
      System.out.println("Student Name: " + Name);
      System.out.println("Age: " + age);
      System.out.println("CGPA: " + CGPA);
   }
      

}

Note:Here we are seeing some things named public,private etc.These are called access specifiers.

• public: Accessible everywhere.
• private: Accessible only within the defining class.
• protected: Accessible within the package and by subclasses.
• default: Accessible only within the package.

Welcome to the realm of Object Oriented Programming(2nd Chapter)

Today we are going to learn about classes and objects.Let's talk about objects of classes.

Object:

In Object-Oriented Programming (OOP), an object is a specific instance of a class, representing a "thing" that has data and behavior.

Think of it Like This: A class is like a blueprint (e.g., a plan for a Student). An object is the actual thing created from that blueprint (e.g., an individual student with Name,age and CGPA).

public class Main {
    public static void main(String[] args) {
        Student student=new Student();
        student.Name="Sakib";
        student.age=23;
        student.CGPA= (float) 4.00;
        student.DisplayInfo();
    }
}

Here 'student' is a object of Student class.We have assigned the values of the student.After tghat we are displaying the informations.

Constructors:

Now we will talk about constructors and destructors.

 class Car {
    String brand;
    int speed;


    Car() {
        brand = "Unknown";
        speed = 0;
    }


    Car(String brand, int speed) {
        this.brand = brand;
        this.speed = speed;
    }

    void display() {
        System.out.println("Brand: " + brand + ", Speed: " + speed);
    }
}

public class Main {
    public static void main(String[] args) {
        Car car1 = new Car(); 
        car1.display();

        Car car2 = new Car("Toyota", 120); 
        car2.display();
    }
}