OOP or object-oriented programming is a type of programming method which is based on the concept of objects. Java has firmly established itself as one of the most used computer programming languages and is thus an object-oriented language. But before delving deeper into Java, it would be useful to first appreciate the ideals that this programming perspective embodies. This article aims to touch on the fundamentals of OOP in Java including its definition, principles, and benefits where its application in Java is pursued in detail.

The aim of OOP is to model real-world entities using objects so that the programs are easier to understand and maintain. By the end of the article, we hope that you will have a better understanding of OOP concepts in Java and the advantages of this approach to writing efficient and high-quality modular programs.

1. The Basics of Object-Oriented Programming

If you are using Java, then you have definitely bumped into the term object. It appears that there is an active use of OOP in software development, as the programming model is becoming a must in software engineering. The object is an instance which is created on the basis of some class, while class is a template for creating objects. Each object can include both the data and the methods that correspond to the data.

OOP enables the structure of the java programs to be more organized, and as a result, java programs are easier to manage, scale and maintain. Encapsulation, abstraction, inheritance and polymorphism are the four principles that provide these functionalities. These principles greatly assist in writing programs that are complex yet serve the purpose of code efficiency, code flexibility and code maintainability.

2. Core Principles of Object-Oriented Programming

2.1 Encapsulation

In software development and Object Oriented Programming, encapsulation is often referred to as the bundling of data (variables) and the methods of the data into a single class structure. The idea of this principle was to protect data from being altered or used in illegitimate manners by hiding certain components of an object and restricting its access. The core idea behind encapsulation is to conceal the implementation details of an object and provide only a controlled way to interact with it.

Access modifiers in Java where, private, protected and public allows the encasement into all the members of the classes. Those modifiers are all about controlling the visibility of methods and variables. As per the class design, all the data members (variables) should be private so that there is no direct access but the option of having control over the accessibility is provided by accessors (getter) and mutators (setter) methods.

Through encapsulation, a program becomes both more secure and more modular. This modularity permits a modification of the internal structure of an object while its other parts of the program that use the object remain stable.

2.2 Abstraction

One of its definitions is what abstraction means is that certain complex implementation details of a system are hidden behind a simplified interface that is exposed to the user. The mindset is directed towards what an object does as opposed to how it implements its functionality. In the context of Java, abstraction is realized by using abstract classes and interfaces.

An abstract class can declare methods to be implemented in subclasses in addition to stating code for some methods in it. These methods without code are called instance methods. An interface is an abstract class but there is no part of the class that has code and this means that the class is just a contract that a class must implement.

The main idea provides programmers with high level functionality and drags away the tips which are deemed not useful. It makes the system more understandable and also increases the scope of flexibility as different classes can implement the abstract methods in their own different ways.

2.3 Inheritance

One of its distinguishing features is its capability to allow a class to inherit the properties and methods of another class. This class which possesses features is called the subclass or derived class while the class from which these features are inherited is referred to as superclass or parent class. An advantage of inheritance is that it enables one to reuse code therefore minimizing redundancy and better architectural design.


In the Java language inheritance is denoted by the word extends. A subclass is said to inherit the methods and fields of a superclass so that part of the behavior is inherited and has to be overridden in the subclass. However, subclasses may also define their own methods and fields. There is an intuitive hierarchy with inheritance; the common behavior and properties are inherited from the parents while more specific behaviors are defined by the children.

This is a very beneficial principle since it facilitates the creation of a system that is both dynamic and expandable. For example, in a system where several vehicle designs exist, all vehicles are likely to have some characteristics and behaviors (speed, fuel capacity, etc.) that are likely to be set in a parent class while other characteristics or behaviors (such as an airplane's ability to fly or a boat's ability to sail) will be unique to each class.

2.4 Polymorphism

In polymorphism, objects can be treated as instances of their parent class regardless of what subclass they belong to. It means many shapes and is useful in implementing a single interface to many different types of objects, hence there are two types of polymorphism in Java namely .compile-time polymorphism and runtime polymorphism.

When methods have the same name but vary in the number of parameters or the type of parameters used, that is termed as Compile-time polymorphism (also method overloading). In this case, a Java compiler makes the decision on which method to invoke based on the arguments that were passed during compilation.

The situation where a method was previously defined in a superclass and is defined again in the subclass is termed as Runtime polymorphism (also called method overriding) and it also happens in this instance. In such a situation, Java makes the decision of which version of that method to invoke based on the object for which that method was invoked at that time.

Writing methods and classes that would be required to carry out the same functions on different kinds of objects is made possible by polymorphism, and it greatly enhances reusability. It minimizes the use of complex conditional statements when coding which enhances maintainability and conciseness of the code.

3. Classes and Objects in Java

In Java, a class serves as a blueprint or template for creating objects. In other words, a class describes the attributes (variables) and capabilities (methods) of all the objects instanced from it. An object can be defined as an instance of a class which is a particular implementation of that class.

For instance, let us assume there is a class named `Car`. Such a class may define properties such as 'color', 'model', 'engine type' and methods such as `start()`, `stop()`, `accelerate()`, and so on and so forth. By having this class, when one wants to have a certain type of car such as 'Honda Civic', this person first creates an object through class `Car` that identifies the specific car.