In this article, we will learn about the basics of OOPs. Object-Oriented Programming is a paradigm that provides many concepts, such as inheritance, data binding, polymorphism, etc.

Object means a real-world entity such as a pen, chair, table, computer, watch, etc. Object-Oriented Programming is a methodology to design a program using classes and objects. It simplifies software development and maintenance by providing some concepts:

• Object
• Class
• Inheritance
• Polymorphism
• Abstraction
• Encapsulation

Objects

Any entity that has state and behavior is known as an object. For example, a chair, pen, table, keyboard, bike, etc. It can be physical or logical. An object contains an address and takes up some space in memory.

Class

Collection of objects is called class. It is a logical entity.

A class can also be defined as a blueprint from which you can create an individual object. Class doesn’t consume any space.

Object and Class Example: main within the class

//Defining a Student class.  
class Student{
    int id;       //field or data member or instance variable  
    String name;
    //creating main method inside the Student class  
    public static void main(String args[]){
        //Creating an object or instance  
        Student s1=new Student();//creating an object of Student  
        //Printing values of the object  
        System.out.println(s1.id);//accessing member through reference variable  
        System.out.println(s1.name);
    }
}  

Here, it defines a class named Student with two fields (id and name). It then creates an instance of theStudent class (s1) and prints the values of its fields.

The Student class contains the main method which serves as the entry point of the program. After that an object of the ‘Student‘ class named ‘s1’ has been created using the ‘new‘ keyword.

//Output
0 
null

Object and class Example: main outside the class

In real time development, we create classes and use it from another class. It is a better approach than previous one. Let’s see a simple example, where we are having main() method in another class.

//Creating Student class.
class Student{
    int id;
    String name;
}
//Creating another class TestStudent1 which contains the main method  
class TestStudent1{
    public static void main(String args[]){
        Student s1=new Student();
        System.out.println(s1.id);
        System.out.println(s1.name);
    }
}  

This above program defines a Student class with two fields (id and name). It also creates another class named TestStudent1, which contains the main method. In the main method, an object of the Student class is created, and its fields are printed.

//Output
0 
null