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Post By Admin Last Updated At 2021-03-20
Java OOPs Concepts- Object-Oriented Programming in Java

We know that Java is one of the leading and powerful programming languages with a lot of useful features. The concept of object-oriented programming is a model of programming that includes inheritance, polymorphism, encapsulation, abstraction, etc. concepts. Java OOPs concepts also implement real-time entities like data binding, abstraction, etc. It is considered that Simula and Smalltalk are the first OOPs programming model that represented object-oriented coding. The major principle behind object-oriented programming is the implementation of real-world concepts of abstraction, inheritance, object, classes, etc. 

There are many popular coding languages like C, C++, Python, Java, etc. are also following the OOPs concepts. Moreover, the OOPs concepts help to build objects, classes and reuse them throughout them in the program and modify them to get the results.

Hence, this concept is widely useful in modern programming languages like Java, Python, etc.

In other words, object-oriented programming is the model where developers define the data model of data structure. Also, the different types of operations applicable to the data structure. 

Majorly, the OOPs concepts include the following things-








Moreover, the other concepts that object-oriented design include are cohesion, coupling, association, aggregation, etc. 

Thus, you have seen the basic idea of OOPs what actually is. Now, let us move further in this concept to know about the Java OOPs Concepts in detail.

Java oops concepts with real-time examples

The following are the most widely used Java OOPs concepts along with some real-time examples.


A class is one of the basic Java OOPs concepts which is a group of objects and is a logical entity rather than a physical entity. Let’s understand this Java oops concept through an example. Suppose, a person holds a class with the name “Expensive Motorbikes”. And it could include objects like KTM, Honda, Bajaj, BMW, etc. Its data can be the price or speed of these motorbikes with specifications. Moreover, it may include the methods that may be performed with these bikes like smooth driving, disk brakes, etc. 

A class includes the following components- modifiers, class name, superclass, interfaces (if any), and body. 

Java OOPs Concepts

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An object is nothing but an instance of the class having a state and behavior. For instance, pen, pencil, table, chair, etc. are objects with a state and behavior either physical or logical. Moreover, an object includes some space in the memory along with an address. The object in the Java OOps concepts includes both data and functions and it operates on the data. These objects can communicate with each other without knowing the code or data details of other objects. 

For example, A cat is an object as it has a state like color, body structure, sensitive paws, etc. And it has a behavior also like chattering, rubbing, rolling, scratching, etc. 


In Java OOPs Concepts, inheritance is the acquisition of all the properties and behaviors of the main object. It offers code reusability and builds a parent-child relationship among two different classes. Here, a child class is a class that inherits properties and the main or parent class is that whose properties are inherited. 

Further, inheritance is categorized into four different types as- Single inheritance, Multilevel inheritance, Hybrid, and Hierarchical inheritance. 

Let us know these inheritance types in detail.

Single Inheritance

In this type of inheritance, Class A inherits the properties of another Class B. Here, it allows a derived class to inherit the properties and behavior of the main parent class. Also, it allows reusing the current code along with adding new features to that code. 

Example code

Class C


- - -


Class D extends Class C {

- - -


Multilevel Inheritance

In Java OOPs Concepts, a multilevel inheritance is nothing but a chain of inheritance. For example, there are three classes B, C, and D. Here, class C inherits the properties & behavior of class B, and the D class inherits the same from the C class. The class here refers, that class B is the parent/main class for class C., And for the D class, the class is the main or parent class. The following image represents the example for this.

Example syntax of the same -

Class B


- - -


Class C extends Class B {

- - -


Class D extends Class C {

- - -


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Hierarchical Inheritance

In Java OOPs Concepts, hierarchical inheritance refers to when two or more than two classes derive from a single class. In other words, two or more classes inherit the properties or behaviors of a single class, then it is known as hierarchical inheritance. For example, we have three classes B, C, and D among which Classes C & D are derived from the parent class B. They acquired the properties and behavior of the main class B, here. The following image can explain well this concept.

Hybrid Inheritance

In the Java OOPs Concepts, hybrid inheritance type is a combination of multiple and multilevel inheritances. But the hybrid and multiple inheritances are not supported in Java programming and these are supported through interfaces only. For an instance, we have four classes, B, C, D, and E. Here, class B is the parent class of C and D classes, where C and D classes are the main/parent classes for the E class. Thus, class E is the only child class in this inheritance type.

Hence, we have gone through the various inheritance types and now we will learn further in Java OOPs concepts.


Within Java OOPs concepts, encapsulation refers to the binding of code and data together into a single unit. Such as; a medical capsule that includes the combination of multiple medicines is the best example of this. A fully encapsulated class in Java protects the data members from any modification or change. Hence, the encapsulation hides and saves the methods & variables of a class data from outside intrusion. 

Moreover, the encapsulation in Java can be achieved through two different methods. Such as declaring the class variables as hidden or private and the setter and getter methods of modification. 

By providing the setter or getter methods, we can make the class data read-only or write-only. Through this method, we have proper control over the class data. Also, it allows data hiding that protects it from any unauthorized access to change or alter it. The method is also very easy and useful for unit testing. 


In Java OOPs concepts, data abstraction is the process of hiding the application details and presenting the essential things to the user. In other words, the abstraction method shows the work of the objects rather than the event of working.

For example, when we see a call that we get on our mobile, it contains two options- receive & reject. We can do either thing but we don’t know how much coding runs behind this operation of a call. Hence, this is the main picture behind abstraction. 

In Java, there are two methods to achieve abstraction- Abstract Class, and Interface.

Abstract class:- An abstract class in Java is the class that is declared abstract. In case the class is declared abstract, then we cannot build objects of the abstract class or cannot instantiate. This class is declared through an Abstract keyword and can include abstract and non-abstract methods. Moreover, this class can contain constructors and static methods also.

For example;

abstract class E{}

Interface: An interface within the concept of Abstraction in Java is the bundle of abstract methods and static constant methods. Here, each method is public and abstract but doesn’t include any constructor. Moreover, the concept of interface is useful to achieve the multiple and hybrid inheritance within Java programming.

Example- Take a real-world example of a man driving a motorbike He only knows that raising the accelerator and operating gear will increase the speed of the motorbike. And applying brakes will stop the motorbike from running. But he does not know exactly about how by raising the accelerator the speed is actually increasing. Also, he does not know about the mechanism of the motorbike or the application of accelerator, brakes, etc. in that motorbike. This is the method of abstraction.


The concept of polymorphism in Java OOPs concepts is that using which a user can perform a single action in multiple ways. By splitting the word we get “poly” means many and “morph” means the forms. Hence, it is the ability of a variable, or a function to take different forms. To understand this concept we can use a real-time example of Bowling in a Cricket match. Here, Bowler is the main class where there are different forms like a fast pacer, slow medium, and a spinner. Thus, a person can be a bowler of any of the different forms available. 

Like that, an object of a class can take different actions or forms in performance.

Moreover, Polymorphism has two forms- compile-time polymorphism, and runtime polymorphism. Overloading a static method within a Java program is an example of compile-time polymorphism. Here, the overloaded method is resolved. It enables a class to include two or more methods with the same name but the arguments passed are different. 

The runtime polymorphism is a type of process where a call made to an overridden method gets resolved at runtime. Here, the reference variable is useful to call the overridden method at run time. 

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A collection of various statements that executes a particular task and returns the outcome to the caller, refers to “Method”. Also, a method can perform a particular task without returning anything in the result. Further, it allows code reusability without having to retype the code. In the Java OOPs concept, the method should be a part of the class different from other coding languages like C++, Python, etc.

The method declarations include the following component types.:-

Access modifier, the return type, parameter list, method type, exception, message passing, and the method body. In this, the access modifier method includes the different access types such as - public, protected, private, and default. 


This is one of the types of Java OOPs concepts where it defines the relationship between two variables. Also, it describes the diversity between these objects. Within this concept, there is no owner of the object as each object has its individual lifecycle. 


Here, all objects have a separate lifecycle where the child object cannot belong to another parent object. For example, we should consider class/objects department and employee. A single employee cannot belong to all the departments of an organization. Even if we remove a department, the employee object will not get destroyed. 


The composition is the type of Aggregation and its other name is the "death" relationship within the Java OOPs concepts. Here, child objects don’t have a separate lifecycle in this regard. Thus,  when the parent object deletes from the system all child objects will be deleted automatically. For this let’s consider an example of Hotel and rooms. A hotel can have multiple rooms. Any single room can not become a part of two individual hotels. Hence, if a user deletes the hotel, the room will also be removed.

Hence, these are the different Java OOPs concepts in detail and now we will move to the advantages of these concepts.

Advantages of Java OOPs concepts

The Java OOPs concepts provide easy understanding and a clear modular structure of the programs. 

Objects built for the OOPs programs are reusable in other programs so that it saves the development costs notably.

Large program writing is difficult somehow but with the following OOPs concepts, the development team can better design them. It may incur fewer flaws in writing these programs. 

Also, the program modularity increases as the object exist independently. 

Wrapping up

Hence, we have gone through the various Java oops concepts and their aspects. The various concepts like abstraction, encapsulation, polymorphism, etc. describe the Java oops concepts well. It also makes the reuse of the class code. Thus, by learning these things you can make your Java application secure, simple, and easy to reuse code through Java OOPs concepts. If you’re in search of learning Core Java and its various concepts in detail with practical experience, then you’re on the right path. OnlineITGuru offers a broad concept of Core Java by industry experts through Core Java Online Training. Learn the concepts in a clear and simple way with real-time examples.