OOPs Concepts in Java: Explained with Examples

By Sunil Sonkar
7 Min Read
OOPs Concepts in Java: Explained with Examples 1

Java’s simplicity, reliability and adaptability have cemented its place in the ever-changing domain of programming. Its strength stems from the principles of Object-Oriented Programming (OOPs), which enables developers to encapsulate real-world entities within their code. This approach yields software solutions that are both versatile and resilient. Whether you are working on small apps or complex corporate systems, integrating OOPs into Java programming adds an element of excitement to the journey, providing you with a guiding map in the form of its principles and concepts.

Object-Oriented Programming (OOPs) and Its Core Principles

Objects and Classes

At the heart of Java programming lies Object-Oriented Programming (OOPs). It emphasizes the design of programs using classes and objects, introducing key principles to structure data and operations effectively.


Objects are the building blocks of OOPs. These self-contained entities represent real-world entities. These store both data (states) and behaviors (methods).


Classes act as templates for crafting objects, outlining their composition with fields, methods and constructors. These templates are abstract and don’t occupy memory space.


Abstraction focuses on displaying only essential information while hiding the rest. This minimizes complexity and effort in programming, making it more efficient and maintainable.


Inheritance enables one object to inherit properties from another, supporting hierarchical classification. It promotes code reusability by allowing new classes to be built upon existing ones.


Polymorphism, meaning “many forms,” allows a single action to be performed in multiple ways. It is classified into compile-time and runtime polymorphism, enhancing code flexibility.


Encapsulation combines data and code into a single unit, safeguarding them from external interference. This process helps to achieve data hiding and code security.

Coupling and Cohesion

Coupling refers to the relationship between classes, determining their interdependence. Cohesion measures how well the attributes and methods within a class are related, emphasizing single-responsibility classes.


Association represents the connection between objects, whether it is a one-to-one, one-to-many, many-to-one or many-to-many relationship. It showcases the interactions between these objects.


Aggregation is a weak association representing a part-of relationship where parts can exist without the whole.


Composition, unlike aggregation, represents a strong association where parts cannot exist without the whole.


Methods are blocks of code that perform specific tasks and promote code reusability. They can be predefined or user-defined, enhancing the readability and maintainability of code.

Static and Abstract Methods

Static methods belong to a class not an instance, allowing them to be invoked without creating objects. Abstract methods lack implementation and must be declared in an abstract class. They enable method overloading and overriding.

Final Methods

Final methods cannot be overridden by subclasses, ensuring method stability.

.equals() Method

The .equals() method compares two objects for content equality, making it crucial for checking string similarity.

Message Passing

Message passing in Java allows threads to communicate by sending objects. It is essential for processes without shared memory.

The Power of OOPs in Java

Encapsulation, Inheritance, and Polymorphism

By harnessing OOPs principles, Java offers a robust and scalable foundation for developing software applications. Encapsulation safeguards code and data, while inheritance and polymorphism enhance code reusability and readability. The use of interfaces and abstract classes further extends the possibilities of OOPs in Java, facilitating complex system designs.

Object-Oriented Libraries

Java’s Object-Oriented Libraries including the Java Standard Library are a prime demonstration of OOPs’ effectiveness. These libraries encompass a wide array of classes and methods rooted in OOPs principles. By utilizing these pre-existing building blocks, Java developers can enhance their coding efficiency, resulting in more manageable and maintainable code.

Reusability and Maintainability

A major benefit of OOPs is its focus on reusability. In the segment of Java development, this means that code can be crafted once and applied multiple times, fostering efficiency and reducing repetitive work. By employing reusable classes and objects, developers can construct modular and easily maintainable codebases.

Data Redundancy Mitigation

OOPs minimizes data redundancy by consolidating shared functions in a single class, which can be inherited by others, streamlining code for more efficient programs.

Code Maintenance

OOPs promotes easy code modification and maintenance. New objects can be created with minor differences from existing ones, making it simpler to accommodate changes or updates. This makes the code flexible and prevents developers from having to begin anew when making enhancements.

Security and Data Hiding

Through encapsulation and abstraction, OOPs enhances code security. Data is hidden from other classes and can only be accessed through well-defined interfaces. This level of data hiding provides an additional layer of security, preventing unauthorized access to sensitive information.

Design Benefits

OOPs encourages extensive design phases, resulting in better-designed programs. Well-structured class hierarchies and encapsulated objects make code more readable and understandable. Well-designed programs are easier to maintain and extend as the project evolves.

Troubleshooting and Duplicity Prevention

Objects with encapsulation are self-contained. Any issues can be contained within specific objects, preserving the rest of the code. Encapsulation also promotes cleaner and easier-to-maintain code by minimizing code duplication.

Flexibility in Problem Solving

OOPs fosters flexibility in problem-solving. The ability to create new classes with unique attributes and behaviors allows developers to adapt to changing requirements and tackle diverse challenges with ease.

Disadvantages of OOPs Concept


One of the main disadvantages of OOPs is the effort required to create and maintain object-oriented programs. Developing well-structured classes and hierarchies demands careful planning and implementation.


Object-oriented programs are often slower compared to other types of programs. The overhead associated with object creation and method invocation can lead to reduced performance.


OOPs programs tend to be larger in size compared to procedural programs. The additional code for class definitions, methods, and encapsulation contributes to increased program size.

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