Java Tutorial



Java Tutorial

OOPs Concepts in Java


Software development frequently uses the programming paradigm known as object-oriented programming (OOP). OOP concepts are also the foundation of Java, one of the most widely used programming languages. OOPs concept in Java uses objects and their interactions to organize and develop software applications. It enables programmers to develop sophisticated systems that are simple to maintain, expand, and reuse code.


Java uses classes, objects, inheritance, polymorphism, and encapsulation to implement the OOPs concept in Java. Java programmers can use these to create scalable, modular, and adaptable programs. Java programs are composed of classes, and objects are just instances of these classes. Polymorphism lets objects take on several shapes and carry out various activities, whereas inheritance allows classes to inherit attributes and methods from other classes. By hiding an object's core operations, developers can increase object security and usability.

Overall, the OOPs concept in Java offers a reliable and effective method for developing software, making it simple for developers to create excellent, scalable systems. In this tutorial, we'll go into further detail about Java's OOPs ideas and how to apply them to create powerful applications.

List of Java OOPs Concepts (And the Four Pillars of OOPs in Java)


An object's characteristics and behavior are defined by its class, a blueprint or Java template. A class instance called an object has its own distinct state and behavior.  


Classes specify an object's properties, such as its name, size, and functions.


Java supports polymorphism, which enables objects to take on several forms and exhibit different actions based on the environment. Polymorphism comes in two forms: compile-time polymorphism and run-time polymorphism.


The technique of minimizing an object's details of execution and just displaying the user-required information is known as abstraction in Java. Reducing complexity and enhancing code maintainability are two benefits of abstraction. The use of abstract classes and interfaces allows for abstraction. An abstract class can be subclassed but cannot be created. A collection of abstract procedures known as an interface spells out the behavior expectations for an object.


Encapsulation in OOPs protects an object's internal operations from its external world, improving its usability and security. To restrict access to an object's attributes and methods, encapsulation is accomplished by utilizing access modifiers like private, public, and protected. Private members are only accessible inside the same class, whereas public members are available to all users.


In Java, an association is a connection between two objects in which one object makes use of or is connected to the other in some manner. A UML class diagram shows the association, with a line representing the connection between the two items.


In Java, a connection between two separate objects is called composition. One object includes another object as an aspect of its state. Without the container object, the enclosed item is impossible. A class can be composed by adding an instance variable from another class.


Aggregation is a connection between two objects in Java where one object includes another, but the contained object is not part of the container object. Identical to composition, aggregation excludes the contained item from the state of the container object.


Inheritance facilitates code reuse and code duplication. A new class in Java can be built on an existing class and inherit its properties and methods through inheritance. The old class is called a superclass or base class, while the new class is known as a subclass or derived class.

Class in Java OOPs

A class in Java OOPs is a model or template for building objects that specify their characteristics and actions. It is a form of data that the user defines that includes both data and techniques connected to that data.

In Java, a class has numerous elements, such as:

  • Class name

  • Data members

  • Methods

  • Constructors

  • Access modifiers

  • Inner classes

Method and Method Passing

A method in Java is a section of code that completes a specific job. It may be used by constructing an object of the class in which it is specified. The return statement returns a value from a method, while method parameters are used to input data into a method. When many methods have the same name but distinct arguments, this is known as method overloading. 


public class Example {
    // Method with no parameters
    public void printMessage() {
        System.out.println("Hello, World!");
    // Method with one parameter
    public void printMessage(String message) {
    // Method with two parameters
    public void printMessage(String message, int times) {
        for (int i = 0; i < times; i++) {
    // Method with return statement
    public int addNumbers(int a, int b) {
        return a + b;
    public static void main(String[] args) {
        Example obj = new Example();
        // Invoking methods
        obj.printMessage(); // Output: Hello, World!
        obj.printMessage("This is a message"); // Output: This is a message
        obj.printMessage("This is another message", 3); // Output: This is another message (printed three times)
        int sum = obj.addNumbers(5, 10);
        System.out.println(sum); // Output: 15

Method Parsing

The act of sending arguments to a method when it is called is known as method parsing in Java. When a method is defined, one or more of the arguments in its parameter list may be declared. Actual values must be given in place of those arguments when the method is invoked. Method parsing is the process of defining the method with these real values.


public class MessagePassing {
    public static void main(String[] args) {
        Person person = new Person("John", 25);
        person.introduce(); // Sends a message to the person object to introduce itself
class Person {
    private String name;
    private int age; 
    public Person(String name, int age) { = name;
        this.age = age;
    public void introduce() {
        System.out.println("Hi, my name is " + name + " and I am " + age + " years old.");

Access Modifier

Access modifiers in Java OOPs are keywords that specify whether a class, method, or variable is accessible to users of other portions of the program. In Java, there are four main access modifiers: public, protected, private, and default.

There are some more access modifiers as well:

  • Return Type: A method's return type identifies the kind of value that will be returned when the method is invoked.

  • Method Name: A method's name serves as a distinctive identifier and is used to invoke the method from other areas of the program. 

  • Parameter list: The list of data variables supplied to a technique when referred to is known as the parameter list, and commas separate it.

  • Method body: Code is contained in the method body when a method is called.


public class AccessModifierExample {
    // Public method with no parameters
    public void publicMethod() {
        System.out.println("This is a public method");
    // Protected method with one parameter
    protected int protectedMethod(String str) {
        System.out.println("This is a protected method with parameter: " + str);
        return 1;
    // Private method with two parameters
    private void privateMethod(int a, int b) {
        System.out.println("This is a private method with parameters: " + a + ", " + b);
    // Default method with no parameters
    void defaultMethod() {
        System.out.println("This is a default method");
    // Main method
    public static void main(String[] args) {
        AccessModifierExample obj = new AccessModifierExample() 
        // Call the public method
        // Call the protected method
        int result = obj.protectedMethod("Hello");
        System.out.println("Result of protected method: " + result);
        // Call the private method
        obj.privateMethod(2, 3);
        // Call the default method

Message Passing

Message passing is a method used in object-oriented programming where objects can interact with one another by sending messages. The request to run a method and any relevant arguments are contained in a message. The message-receiving object then applies the necessary method and returns any output to the sender.

Java uses the method invocation to implement message passing. A message is sent to another object by using one of its methods when one object wishes to establish a relationship with another.

Other OOPs concepts in JAVA

Dependency: This is a relationship between two classes where one class uses the functionality provided by another, but the relationship is not as strong as in association. The class used is not a part of the class using it and can be replaced by another class that provides similar functionality.

Overloading: This refers to writing many methods into a class with the same name but distinct inputs. This enables the use of the same method name for many activities.

Overriding: This is the process of writing a method with the same declaration as a method in a superclass in a subclass. The subclass can offer its own adaptation of the method due to overriding.

Static binding: During compilation, a method call is linked to the method code in this manner. The type of the reference variable determines which method has to be called.

Dynamic binding: During runtime, a function call is connected to the method code through a process known as dynamic binding. The class of the object that the value of the reference parameter refers to determines which method should be invoked.

It is vital to comprehend these ideas to create scalable and maintainable Java programs.

What is Coupling in Java OOPs?

The level of reliance among classes or modules in an application is called coupling in Java OOPs. It gauges the degree to which two or more classes are connected.

Modifications made to one class can majorly affect other classes that depend on it in a system with tight coupling. Because of this, it could be challenging to uphold and change the system over time. On the other hand, a system with loose coupling is one in which modifications to one class have little or no effect on other classes.

Best Practices for OOPs Concepts in Java

The following are some best practices for Java's OOPs concepts:

  • To encapsulate data, use access modifiers like private, protected, and public, and offer public means for accessing and editing it.

  • It may be a helpful tool for class organization and code reuse, but it can also result in complicated class hierarchies and difficult-to-maintain code. Use inheritance wisely, and stay away from complex class hierarchies.

  • Because composition allows for more flexibility and simpler maintenance, it is frequently preferable to inheritance.

  • Use appropriate names for classes, methods, and variables, and adhere to accepted naming standards like camelCase or PascalCase.

  • Use interfaces to establish a collection of shared methods that various classes can use, maintaining consistency across various implementations.

  • Keep your methods concise and single-task-focused by breaking up larger ones into smaller, more targeted ones.

  • To enhance code quality and lower maintenance costs, avoid duplicating code and refactor it into reusable methods or classes.

By adhering to these best practices, you can design clear, reliable code that is simple to comprehend and alter.


Object-oriented programming (OOPs) has revolutionized the software development industry. Writing complicated, extensive programs that are simple to comprehend, maintain, and alter has become simpler because of OOPs ideas like encapsulation, inheritance, polymorphism, and abstraction.

With OOPs, code structure and reuse have been considerably increased, making it simpler for developers to collaborate and speed up development. Programming would be far more challenging, disorganized, and ineffective without OOPs.

OOPs continues to be a key component of contemporary software development, and developers must have a firm grasp of OOPs' ideas to create reliable and scalable systems.


1. What is OOP in Java?

Object-oriented programming (OOP) is a paradigm for organizing code and data using objects and classes.

2. What are the four foundational principles of Java OOP?

Encapsulation, inheritance, polymorphism, and abstraction are the four foundations of Java OOP.

3. Why is Java OOP important?

OOP is crucial in Java because it facilitates the development of intricate, expansive programs and makes code more streamlined, manageable, and reusable.

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