OOP is one of the most fundamental programming concepts. Let’s explore the four main OOP concepts in Java and discuss how each works.
Java is one of many programming languages and technologies supported by Netreo’s leading tools, Retrace and Prefix. At Netreo, we aim to help developers become better. Let’s take a look at some of the foundational Java programming language concepts with a primer on OOP concepts in Java.
Object Oriented Programming (OOP) is a programming paradigm that focuses on the use of objects to represent and manipulate data. In OOP, data is encapsulated within objects, and objects are defined by their properties (attributes) and behaviors (methods). OOP provides several key concepts that enable developers to write modular, reusable, and maintainable code.
In the previous section, we’ve said that objects have properties and behavior, but we didn’t really define the concept. Let’s do it now.
To explain what objects are, it’s probably a good idea to start by explaining what objects aren’t. So, programming languages that aren’t object oriented tend to have a stark separation between data and behavior. Basically, you have data represented by data structures, and behavior is implemented by functions that act on said data structures.
An object is sort of a blend between the two, since it has both data and behavior. Each object represents an instance of a certain domain concept or entity (e.g. a User, a Product, a Transaction), stores the data associated with that instance, and expose methods that potentially change that data.
A big difference between OOP and non-OOP is that an object should expose behavior and hide most or all of its data. This is part of encapsulation, a key OOP concept we’ll cover in more detail next.
The main ideas behind Java’s Object-Oriented Programming, OOP concepts include abstraction, encapsulation, inheritance and polymorphism. Basically, Java OOP concepts let us create working methods and variables, then re-use all or part of them without compromising security. Grasping OOP concepts is key to understanding how Java works.
Java defines OOP concepts as follows:
OOP concepts in Java work by letting programmers create components that are reusable in different ways while maintaining security.
Abstraction lets programmers create useful and reusable tools. It enables programmers to create complex systems by breaking them down into smaller, more manageable components. For example, a programmer can create several different types of objects, which can be variables, functions or data structures. Programmers can also create different classes of objects as ways to define the objects.
For instance, a class of variable might be an address. The class might specify that each address object shall have a name, street, city and zip code. The objects, in this case, might be employee addresses, customer addresses or supplier addresses. In addition, abstraction provides a mechanism for hiding the implementation details of a class or method from the outside world and providing a simplified interface for clients to interact with. In Java, you can achieve abstraction through two main mechanisms: abstract classes and interfaces.
Encapsulation lets us reuse functionality without jeopardizing security. It’s a powerful, time-saving OOP concept in Java. For example, we may create a piece of code that calls specific data from a database. It may be useful to reuse that code with other databases or processes. Encapsulation lets us do that while keeping our original data private. It also lets us alter our original code without breaking it for others who have adopted it in the meantime.
Encapsulation provides several benefits, including:
In Java, encapsulation is implemented using access modifiers, which control the visibility of variables and methods within a class.
The three access modifiers in Java are:
Encapsulation enables developers to write cleaner, more organized, and more secure code. By controlling access to variables and methods, encapsulation promotes good software design practices and helps to manage the complexity of large-scale projects.
Inheritance is another labor-saving Java OOP concept that works by letting a new class adopt the properties of another. We call the inheriting class a subclass or a child class. The original class is often called the parent or the superclass. We use the keyword extends to define a new class that inherits properties from an old class.
The subclass inherits all the public and protected variables and methods of the superclass, and it can also define its own variables and methods. This makes it possible to create a hierarchy of classes, where each subclass inherits from its superclass and adds its own unique features.
Inheritance provides several benefits, including:
Inheritance allows developers to create complex class hierarchies with shared functionality and unique features. By promoting code reuse, polymorphism, and flexibility, inheritance enables developers to write more efficient and maintainable code.
Polymorphism in Java works by using a reference to a parent class to affect an object in the child class. We might create a class called “horse” by extending the “animal” class. That class might also implement the “professional racing” class. The “horse” class is “polymorphic,” since it inherits attributes of both the “animal” and “professional racing” class.
Two more examples of polymorphism in Java are method overriding and method overloading.
In method overriding, the child class can use the OOP polymorphism concept to override a method of its parent class. That allows a programmer to use one method in different ways depending on whether it’s invoked by an object of the parent class or an object of the child class.
In method overloading, a single method may perform different functions depending on the context in which it’s called. This means a single method name might work in different ways depending on what arguments are passed to it.
Polymorphism provides several benefits, including:
Polymorphism allows for more flexible and adaptable code. By enabling objects of different classes to be treated as if they are of the same class, polymorphism promotes code reuse, simplification, and flexibility, making it an essential component of Object-Oriented Programming.
Now that we explained the foundational OOP concepts in Java, let’s look at a few common examples.
In the example below, encapsulation is demonstrated as an OOP concept in Java. Here, the variable “name” is kept private or “encapsulated.”
//save as Student.java
package com.javatpoint;
public class Student {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name
}
}
//save as Test.java
package com.javatpoint;
class Test {
public static void main(String[] args) {
Student s = new Student();
s.setName(“vijay”);
System.out.println(s.getName());
}
}
Compile By: javac -d . Test.java Run By: java com.javatpoint.Test Output: vijay
It’s quite simple to achieve inheritance as an OOP concept in Java. Inheritance can be as easy as using the extends keyword:
class Mammal {
}
class Aardvark extends Mammal {
}
For a full tutorial on the different ways to use inheritance in java, see this blog post.
In the example below of polymorphism as an OOP concept in Java, we have two classes: Person and Employee. The Employee class inherits from the Person class by using the keyword extends. Here, the child class overrides the parent class. For the full example, see this blog post.
class Person {
void walk() {
System.out.println(“Can Run….”);
}
}
class Employee extends Person {
void walk() {
System.out.println(“Running Fast…”);
}
public static void main(String arg[]) {
Person p = new Employee(); //upcasting
p.walk();
}
}
Object-Oriented Programming (OOP) has become widely popular due to its many advantages over other programming styles such as Procedural Programming and Functional Programming.
Procedural Programming is a programming style that is based on a set of procedures or functions, where each function is a sequence of instructions that performs a specific task. It focuses on the sequence of must-follow steps that to accomplish a specific task. In contrast, OOP focuses on the objects and their interactions to solve problems.
Functional Programming is a programming style that focuses on the use of functions that produce output based on their input, without modifying any external state. It is based on mathematical functions and is characterized by immutability and statelessness. In contrast, OOP is based on objects and their states, and it is designed to manage complex, stateful systems.
Here are some key differences between OOP and other programming styles:
OOP enables encapsulation, inheritance, code reusability, and flexibility, making it a powerful tool for building complex, stateful systems.
Java packages aren’t really an OOP concept per se, but it is essential in Java programming, so we’ve figured it’d make sense to cover it briefly.
In any medium-sized to large application, you’ll probably end-up with many, many classes. It’s useful to keep classes that represent similar concepts together, while keeping the different ones apart. In other words, it’s beneficial to have some kind of grouping ability when it comes to classes.
That’s exactly where packages come in handy. Packages allow you to organize your classes, grouping them by functionality, hierarchy, and separation of concerns. Java packages also solve the problem of naming conflicts: you can have as many classes with the same name as you’d like, as long as they belong to different packages.
The goal of OOP concepts in Java is to save time without sacrificing security and ease of use. The following best practices are all oriented toward advancing that main goal.
For a good, full list of best practices for OOP concepts in Java, see this blog post. You can also check out our article about OOP concepts in C#.
These concepts and best practices are only as great as the developers that implement them. To make your work better, you need productivity tools to improve your Java programming.
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