OOP's primary goal is to bind together the data and the method that use them so that only that function and no other part of the code can access the data. The first programming language that was genuinely object-oriented is smalltalk.

Object-Oriented Programming Concepts are as follows:

1. Class

2. Object

3. Method

4. Pillars of OOPs

• Inheritance
• Polymorphism
  • Compile-time polymorphism
  • Runtime polymorphism
• Abstraction
• Encapsulation

In addition to these concepts, there are a few other terms used in Object-Oriented design:

1. Association

2. Aggregation

3. Cohesion

4. Coupling

5. Composition

Object-Oriented Programming Concepts

Class:

• In object-oriented programming (OOPs), Classes serves as a tailored blueprint, a precise model used for creating object A class is essentially a blueprint or template that defines the properties and behaviors of objects. OOP classes lassencapsulates both data (in the form of variables) and methods that operate on that data.
• In general, class declarations can contain the following parts :

• Class name:we should declare class name when defining class.By convention, the class name should begin with the first letter capitalised.
• access modifier :A class may be public or have default access as a modifier .
• Superclass (if needed): If there is one, the term extends is followed by the name of the superclass. Only one parent can be extended (subclassed) by a class.
• Interfaces (if needed): A list, separated by commas, of the interfaces that the class, if any, implements. A class may support several interfaces.
• Body :Code inside the class body is surrounded by braces {}

Class structure

Object :

• A fundamental building block of object-oriented programming, an object represents actual physical entities. Many objects are created by a normal Java programme, and as you are aware, these objects interact via calling methods
• The parts of your code that are visible to the viewer or user are the objects, which carry out your code
• In general, object declarations can contain the following parts :

• State:: An object's properties serve as a representation of it. Additionally, it reflects an object's characteristics.
• Behavior :An object's methods act as a representation of behaviour. Additionally, it demonstrates how one object responds to others.
• Identity :An object's identity is its special name, which enables it to communicate with other things.
• Method :A method is a group of statements that work together to complete a certain job and provide the outcome to the calling. A method can operate with no output. Since we can reuse the code with methods instead of having to type it all over again, they are regarded as time savers. In contrast to languages like C, C++, and Python,
  Java requires that every method be a component of a class.

Object structure

 // Java  program using class and object   

public class Student{
    static String Student_name;
    static int Student_id;
 
    static void set(String name, int id) {
    	Student_name  = name;
    	Student_id  = id;
    }
 
    static void get() {
        System.out.println("Student name is: " +Student_name );
        System.out.println("Student id is: " + Student_id);
    }
 
    public static void main(String args[]) {
    	Student.set("Dr Alok Raja", 1403195);
        Student.get();
    }
}

Student name is: Dr Alok Raja 

Student id is:14031952 

Inheritance :

• Inheritance occurs when one object inherits all of the properties and behaviours of a parent object. It allows for code reuse. It is employed in order to achieve runtime polymorphism.
• Object-Oriented Programming (OOP) heavily relies on inheritance. In Java, inheritance is the mechanism that enables one class to inherit the features (fields and methods) of another class.
• Inheritance promotes the concept of "reusability," where we can create a new class by deriving it from an existing class that already contains some of the code we need. This allows us to use the existing class's fields and methods, encouraging code reuse.

• Superclass:: The class whose characteristics are inherited is referred to as the superclass (also known as base or parent class).
• Subclass :The class that inherits the other class is referred to as a subclass (also known as derived or extended or child class). In addition to the superclass's fields and methods, the subclass can add its own.

Polymorphism :

• Polymorphism used when one task is performed in multiple ways. To persuade a customer to change their mind, for example, draw a shape, triangle, rectangle, etc.
• To achieve polymorphism in Java, we use method overloading and method overriding.
• Polymorphism is the ability of object-oriented programming languages to efficiently differentiate between entities sharing the same name. In Java, this is achieved by utilizing the unique signatures and declarations of these entities.

Abstraction :

• Abstraction is the method of hiding internal information while displaying functionality.
• The capability of data abstraction allows the user to only see the most important information. Simple or unnecessary units are not displayed to the user.
  Ex: A computer is regarded as a whole rather than as its component parts.

Encapsulation :

• Encapsulation is the process of binding (or wrapping) code and data into a single unit.
• It is defined as the consolidation of data into a single unit. It is the mechanism that connects the code and the data that it manipulates. Encapsulation can also be thought of as a protective shield that prevents code from accessing data outside of the shield.




• Because all of the data members are private in this class, Java Bean is the fully encapsulated class.
• Because all of the data members are private in this class, Java Bean is the fully encapsulated class.
• Encapsulation can be accomplished by writing public methods in the class to set and get the values of the variables and by declaring all of the variables in the class as private.

Association

• The relationship between the things is represented through association. In this case, one object can be associated with one or more objects. There are four possible types of relationship between the things.

• One to One
• One to Many
• Many to One
• Many to Many

Aggregation

• Aggregation is a method of achieving Association. Aggregation denotes the relationship in which one thing includes other objects as part of its state. It symbolises the weak connection between objects. In Java, this is known as a has-a connection. For example, the is-a relationship is represented by inheritance. It is another another method of reusing items.

Cohesion

• The level of cohesion of a component that performs a single well-defined task. A highly cohesive method completes a single well-defined task. The task will be divided into sections using the weakly cohesive method. Because it contains I/O-related classes and interfaces, the java.io package is highly cohesive. The java.util package, on the other hand, is a weakly cohesive package because it contains unrelated classes and interfaces.

Coupling

• The knowledge, information, or dependency of another class is referred to as coupling. It occurs when classes are aware of one another. There is strong coupling when one class has the details information of another class. To display the visibility level of a class, method, or field in Java, we use the private, protected, and public modifiers. Because there is no concrete implementation, you can use interfaces for the weaker coupling.

Composition

• Association can also be accomplished through composition. The composition denotes a relationship in which one object contains other objects as part of its state. The containing object and the dependent object are inextricably linked. It is the condition in which containing objects do not exist independently. When you delete the parent object, all of the child objects are also deleted.

Comparison Chart

Difference Between Object-Oriented and Procedure Programming languages are mention below