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OOPS Concepts in Java
Logicmojo - Updated Jan 15, 2024

In this blog, we'll go over the fundamentals OOPS Concepts in Java. Object-oriented programming (OOPS) Concepts in Java programming model that includes ideas such as inheritance, abstraction, polymorphism, and others. These ideas are aimed at incorporating real-world entities into computer applications. They develop working techniques and variables that they may reuse without jeopardising security. This places a greater emphasis on data than on functions. Java, C++, C#, JavaScript, Python, Ruby, Perl, Smalltalk, and other object-oriented programming languages are among the most frequently used and significant.

Inheritance, hiding, polymorphism, and other real-world concepts are all part of object-oriented programming. The core purpose of OOP is to connect data and the functions that operate on it so that only that function may access it.

Object-oriented programming has a number of advantages over procedural programming.:

🚀 OOP is a more efficient and straightforward method of programming.
🚀 The programmes have a clear structure thanks to OOP.
🚀 OOP helps to keep Java code DRY (Don't Repeat Yourself), making it easier to maintain, alter, and debug.
🚀 OOP allows developers to design full reusable applications with less code and less time.

Learn More

OOPS Concepts in Java

1. What do you mean by OOPS?

Object-oriented programming (OOP) is a programming technique that employs classes and objects to create a programme. Object-oriented programming is also known as Java's core. Object-oriented programming is a programming style that centres a programme on objects with well-defined interfaces. This is also known as data control when it comes to accessing the code. Programmers define the data type of a data structure as well as the operations that are done to it in this technique.
A real-world entity such as a pen, chair, table, computer, watch, and so on is referred to as an object. It makes software development and maintenance easier by introducing the following concepts:

  1. Object

  2. Class

  3. Inheritance

  4. Polymorphism

  5. Abstraction

  6. Encapsulation

Aside from these ideas, there are a few other terminology used in Object-Oriented design:

  1. Coupling

  2. Cohesion

  3. Association

  4. Aggregation

  5. Composition

2. What is OOPs concepts in java?

The goal of the OOps Concepts in Java is to improve code readability and reusability by efficiently designing a Java application. Abstraction, encapsulation, inheritance, and polymorphism are the four core ideas of object-oriented programming. These ideas are aimed at incorporating real-world entities into computer applications.
In a nutshell, Java OOP concepts allow us to design working methods and variables, then reuse all or parts of them without jeopardising security. Understanding OOP ideas is critical to comprehending how Java works.

3. What do you mean by Object?

An object is any entity that has state and behaviour. For instance, a chair, pen, table, keyboard, bicycle, and so forth. It could be physical or conceptual in nature.
An instance of a class can be defined as an Object. An object holds an address and occupies memory space. Objects can communicate even if they are unaware of one other's data or code. The only thing that matters is the type of message that is accepted and the type of response that the objects provide.
A dog, for example, is an object since it has states such as colour, name, breed, and activities such as waving the tail, barking, and eating.
A typical Java application creates a large number of objects, which interact via invoking methods. An object is made up of the following elements:

    🚀 State : The state of an item is represented by its characteristics. It also reflects an object's attributes.
    🚀 Behaviour : The behaviour of an object is represented by its methods. It also reflects an object's interaction with other objects.
    🚀 Identity : It gives a thing a unique name and allows it to communicate with other objects.

Assume we've constructed a class called Car, and we've used the term new to indicate the class name followed by the object name.
Example 1 :

Public class Car {
    int y=100;
    Public static void main (String args []) {
    Car Carobj= new Car ();
Try it Yourself

A new object is created in the above example, and it returns the value of y, which may be the number of cars.

Car Carobj= new Car ();

This is the statement that is used to make objects.
We can also construct numerous objects in the same class and access objects created in one class from another. This strategy is utilised for better class organisation, and it is important to note that the java file name and the class name are the same.

Example 2 :

The below example shows how multiple objects are created in the same class and how they are accessed from another class.


Public class Car {
int y=100;
int z=80;


Class Temp {
  Public static void main (String [] args)
        Car Carobj1 = new Car();
        Car Carobj2 = new Car();
        System.out.println (Carobj1.y);
        System.out.println (Carobj2.z);
Try it Yourself

When this programme is compiled, the output is 100, 80.

4. What are Classes?

Classes are similar to object constructors in that they allow you to create objects. A group of objects is referred to as a class. Logic quantities are said to be classes. Classes do not take up any memory space. A class is sometimes known as an object's template. Fields, methods, and constructors are examples of class members. Both static and instance initializers exist in a class.

A class declaration consists of the following elements:

 • Modifiers : Public or default access options are available.
 • Class Name : Initial letter of the class name.
 • Superclass : A class can only extend (subclass) one parent (superclass).
 • Interface : Multiple interfaces can be implemented by a single class.
 • Body : Braces encircle the entire body.
To construct a class, use the class keyword. The following is a simplified generic form of the class definition:

class classname {
type instance variable 1;
type instance variable 2;
type instance variable n;

type methodname 1 (parameter list) {
// body od method 

type methodname 2 (parameter list) {
// body od method 

type methodnamen (parameter list) {
// body od method 

Instance variables are variables or data that are defined within a class. The methods are always full of code. As a result, members of a class refer to the methods and variables declared within it. These methods are not defined as static or public, and they all have the same form as main().

6. What do you mean by Abstraction?

Abstraction is a technique for displaying only the information that is required while hiding the rest. The basic function of abstraction, we can argue, is to hide data. Abstraction is the process of picking data from a huge set of data in order to display the information required, hence minimising programming complexity and effort.
There's also abstract methods and abstract classes. A class that declares one or more abstract methods is known as an abstract class. A method that has a method definition but no implementation is known as an abstract method. The same pieces of data can be used in numerous applications once we've structured our object utilising data abstraction—abstract classes, generic forms of behaviour, and object-oriented programming hierarchy. When two or more subclasses perform the same activity in different ways and with distinct implementations, abstract methods are utilised. An abstract class can have both abstract and regular methods, i.e., both abstract and regular methods.

Let's look at a concrete example of abstraction. Assume we wish to create a student application and request that information about the student be collected.
The following data is gathered by us.

 • Name

 • Class

 • DOB

 • Address

 • Father's name

 • Mother's name

We may not need all of the information we've gathered to complete the application. As a result, we choose the information needed to complete the application. As a result, we fetched, deleted, and chose student information from a vast dataset. Abstraction is the term for this procedure.

Example of Abstraction :

// Abstract class
abstract class Animal {
// Abstract method (does not have a body)
  public abstract void animalSound();
  // Regular method
  public void sleep() {

// Subclass (inherit from Animal)
class Pig extends Animal {
  public void animalSound() {
    // The body of animalSound() is provided here
    System.out.println("The pig says: wee wee");

class Main {
  public static void main(String[] args) {
    Pig myPig = new Pig(); // Create a Pig object
Try it Yourself

7. What do you understand from Inheritance?

Inheritance is a way of acquiring/inheriting the properties of another object, and it also permits hierarchical classification. The notion is that we can develop new classes based on existing classes, i.e., when you inherit from a parent class, you can utilise the parent class's methods and properties. The parent-child relationship is represented by inheritance.
A whale, for example, is classified as a marine animal and belongs to the class mammal, which falls within that category. We employ top-down categorization, or hierarchical classification. If we wish to characterise a more specific group of animals, such as mammals, we would use terms like teeth, cold-blooded, warm-blooded, and so on.
A derived class is another name for this. A superclass is a base or parental class from which properties are inherited by subclasses. Inheritance is primarily used for method overriding.

The extend keyword is used to inherit a class.

Single, multilevel, multiple, hybrid, and hierarchical inheritance are the five forms of inheritance. Let's discuss them in brief one by one,

 • Single Level Inheritance

This one class, referred to as the derived class, inherits properties from its parent. This allows the code to be reused while simultaneously adding new functionality. Class b, for example, inherits properties from class a.
The base or parental class is A, while the derived class is B.

Syntax :

Class a {
Class b extends class a {

 • Multilevel Inheritance

This class is derived from another class, which is derived from another class, i.e., this class has more than one parent class; thus, multilevel inheritance is used.

Syntax :

Class a {
Class b extends class a {
Class c extends class b {

 • Hierarchical level Inheritance

In this case, one parent class can have two or more derived classes, or two or more child classes can have one parent class.

Syntax :

Class a {
Class b extends class a {
Class c extends class a {

 • Hybrid Inheritance

Multiple inheritance is not supported in java since it leads to ambiguity, and this type of inheritance can only be achieved through interfaces.
Consider the fact that class an is the parent or base class of classes b and c, and that classes b and c are the parents or base classes of class d. Class an is derived from class b and class c, whereas class d is derived from class b and class c.
The following programme produces a super class called add and a subclass called sub, with the subclass add being created using the extend keyword.

Syntax :

// a simple example of inheritance 
//create a superclass
Class Add {
    int my;
    int by;
    void num (int xy, int hy) {
//create a sub class
class b extends add {
    int total;
    void sum () {
public Static void main (String args [ ] ) {
    b subOb= new b ( );
    subOb. num (10, 12);
    subOb. Sum ( ) ;
    System.out.println(“total =” + subOb. Total);

Output will be – total = 22

8. What do you mean by Polymorphoism?

Polymorphism is a term that refers to a process that executes a single operation in multiple ways. It happens when we have a lot of classes that are related to each other through inheritance. There are two types of polymorphism: compile-time polymorphism and runtime polymorphism. When we override a static method in Java, this is an example of compile time polymorphism. A call to an overridden method is resolved at run time rather than compile time in run time polymorphism, also known as dynamic method dispatch. The overridden method is always invoked through the reference variable in this method. Polymorphism can be achieved by employing method overloading and overriding.
Polymorphism is frequently expressed as a single interface with many methods. This simplifies things by allowing the same interface to be used for a variety of actions.

Example of Polymorphism :

public class Bird {
Public void sound ( ) {
System.out.println ( “ birds sounds “ );
public class pigeon extends Bird {
public void sound ( ) {
System.out.println( “ cooing ” ) ;
public class sparrow extends Bird ( ) {
Public void sound ( ){
System.out.println( “ chip ” ) ;

We can see a common action sound () in the example above, however there are several distinct ways to do the same action. This is one of the examples of polymorphism in action.

Polymorphism in Java is divided into two categories:

    1.Static / Compile-Time Polymorphism is a type of polymorphism that occurs during the compilation process.
    2.Runtime Polymorphism / Dynamic Polymorphism

9. What is Compile-Time Polymorphism in Java?

Compile-time polymorphism, also known as static polymorphism or early binding, is a type of polymorphism that occurs during the compilation process. A polymorphism that is resolved during the compilation process is known as compile-time polymorphism. The reference variable of a class is used to call overloading of methods. Method overloading and operator overloading are used to achieve compile-time polymorphism.

10. What is Run-Time Polymorphism in Java?

One of the ways Java supports Runtime Polymorphism is through method overriding. The process by which a call to an overridden method is resolved at run time rather than compile time is known as dynamic method dispatch.
When a superclass reference is used to call an overridden method, Java determines which version(superclass/subclasses) of that method should be run based on the type of the object being referred to at the time the call is made. As a result, this decision is determined during runtime.
The type of the object being referenced to (rather than the type of the reference variable) decides which version of an overridden method is executed at runtime.
A subclass object can be referenced via a superclass reference variable. Upcasting is another term for this. At runtime, Java takes advantage of this feature to resolve calls to overridden methods.
As a result, if a superclass has a method that is overridden by a subclass, multiple versions of the method are run when different types of objects are referenced to through a superclass reference variable.

11. Why And When To Use Abstract Classes and Methods?

To achieve security - hide certain details and only show the important details of an object.

12. What do you mean by Encapsulation?

One of the principles of OOPs is encapsulation, which is the process of joining data and code into a single unit and keeping them safe from outside intervention and misuse. The data is concealed from other classes and can only be accessible through the current class's methods throughout this procedure. As a result, it's also known as data obfuscation. Encapsulation functions as a protective covering that prohibits outsiders from accessing the code and data. A well-defined interface is used to control these. Declaring variables as private and offering public setter and getter methods to modify and inspect their values achieves encapsulation. Encapsulation is the process of making a class's fields read-only or write-only.

Example :

class animal {
// private field 
private int age;
//getter method 
Public int getage ( ) {
return age;
//setter method 
public void setAge ( int age ) {
this. Age = age;
class Main {
public static void main (String args []);
//create an object of person 
Animal a1= new Animal ();
//change age using setter 
A1. setAge (12);
// access age using getter 
System.out.println(“ animal age is ” + a1. getage ( ) );

Output: The animal is 12 years old.

We declared a private field named age that can only be accessible within the class in this example.
We used open methods to determine age. These are known as getter and setter methods. We can limit illegal access from outside the class by making age secret. As a result, this is referred to as data concealing.

13. What is Coupling in Java?

The relationship between two classes is referred to as coupling. It denotes how well one object or class understands another. That is, if one class changes its characteristics or behaviour, the dependant modifications in the other class will be affected. As a result, these modifications will be determined by the degree of interdependence between the two classes. Tight coupling and loose coupling are the two types of coupling.

 • Tight Coupling

A class is considered to have tight coupling with another class if it is highly connected to it.

Example :

public class College{
public void status() {
System.out.println("College is open today");
public class Student{
College obj = new College();
public void goToCollege() {

The student class is reliant on the college class in the code example above. That is, each change in the college class necessitates a change in the student class. As a result, the student class and the college class are inextricably linked.

 • Loose Coupling

It is considered to have loose coupling with another class if one class is weakly connected to another. Tight coupling is preferable to loose coupling. Interfaces, as seen below, can assist a class accomplish this.

Example :

public interface College{
void status();
class CollegeStatus1 implements College{
public void status() {
System.out.println("College is open monday to friday");
class CollegeStatus2 implements College{
public void status() {
System.out.println("College is open on saturday");
public class Student{
College obj = new CollegeStatus1();
public void goToCollege() {

CollegeStatus1 and CollegeStatus2 are loosely connected in the code example above. A CollegeStatus1 or CollegeStatus2 class is not directly or firmly associated with the student class in this case. The loose coupling implementation is achieved by using a dependency injection method, which allows a student to go to college with any class that has implemented a college interface. It also means that we can use CollegeStatus2 on Saturdays when the college is open.

14. What is Cohesion in Java?

Cohesion is a metric that assesses how closely a class's methods and attributes are related to one another and how focused they are on completing a single, well-defined purpose for the system. The term "cohesion" refers to a class's ability to have a single, well-defined duty. It's better to retain more unified classes for code reuse. Low cohesive classes are difficult to maintain because their methods and properties have a less logical link. It is usually preferable to have well-coordinated courses in order to keep them focused on a single task.

 • Low Cohension

We have a class called Book in the following code. However, it lacks cohesion because the class's characteristics and methods are less focused and independent. This class should have information about the book in it. As a result of the person name and age procedure, this classless cohesiveness is achieved.

Example :

class Book{
int price = 299; //related attribute
String name = "Sam"; //unrelated attribute
//related methods to Book class
public String author(String name) {
return name;
public String title(String subject) {
return subject;
public int id(int number) {
return number;
//unrelated methods to Book class
public int age(int age) {
return age;

 • High Cohension

It is argued that a class is extremely cohesive when it has a single well-defined goal or task. So, if we eliminate the information about the individual from the preceding sample code, the class becomes quite cohesive, as shown below.

Example :

class Book{
int price = 299; //related attribute
//related methods to Book class
public String author(String name) {
return name;
public String title(String subject) {
return subject;
public int id(int number) {
return number;

15. What is Association in Java?

The term "association" refers to a relationship that exists between two distinct classes and is established via the use of their Objects. It establishes a connection between two or more objects.
One-to-one, one-to-many, many-to-one, and many-to-many associations are all possible. Let us use real-world examples to illustrate this. Consider the relationship between the bus and the passengers. There can only be one driver on a bus (one-to-one). The single bus can be associated with a large number of passengers (many-to-one). A single passenger can travel on a variety of buses (one-to-many). Furthermore, many passengers are familiar with the various buses (many-to-many). To leverage the functionality and services supplied by another object, one object is associated with another object.
It represents HAS-A relationship.

Example :

//class bus
class Bus
private String name;
// bus name
Bus(String name)
{ = name;
public String getBusName()

//passenger class
class Passenger
// passenger name
private String name;
// passenger seat id number
private int seatId;
Passenger(String name, int seatId)
{ = name;
this.seatId = seatId;
public String getPassengerName()
public int getPassengerId()
return this.seatId;

//Association between both the
//classes in the main method
class Demo
public static void main (String[] args)
Bus bus = new Bus("Shree Travels");
        Passenger psg = new Passenger("Reena", 52);
System.out.println(psg.getPassengerName() + " with seat number " + psg.getPassengerId()
+ " is a passenger of " + bus.getBusName());

Output :Reena Travels passenger Sneha has seat number 52.

Explanation: Two different classes, Bus and Passenger, are linked in the preceding example by their Objects inside the Demo class. Using the concept of association, we can construct a relationship between two separate classes in this way. A bus can carry a large number of people, hence it is a one-to-many relationship.
Aggregation and composition are the two types of association.

16. What is Aggregation?

Aggregation is a tenuous link. Aggregation is a relationship between an object and the objects it contains. Aggregation is a term used to describe a part of a larger connection in which a part can live without the whole.
Let's look at the relationship between Group and Person as an example. A person can be a member of several groups. As a result, a Group can contain many individuals. The Person object, on the other hand, will not be destroyed if we delete a Group. The Has-A relationship is represented by aggregation. Aggregation is a one-way relationship with a unidirectional association. For example, the group can have people, but not the other way around, making it unidirectional. Both entries in Aggregation can exist on their own, which means that terminating one will not effect the other.

Example :

import java.util.*;

//person class
class Person
private String name;
private int age ;
Person(String name, int age)
{ = name;
this.age = age;
public String getName() {
return name;
public int getAge() {
return age;

/* Group class contains the list of person
Objects. It is associated with the person
class through its Object(s). */

//group class
class Group
private String groupName;
private List persons;
Group(String groupName, List persons)
this.groupName = groupName;
this.persons = persons;

//main method
class Demo
public static void main (String[] args)
//creating objects of person class
Person a = new Person("Tanmay", 17);
Person b = new Person("Sam", 18);
Person c = new Person("Pitu", 19);
Person d = new Person("Khushi", 20);
//making a list of persons belongs to social welfare group
List p1 = new ArrayList<>();
//making a list of persons belongs to drama fest group
List p2 = new ArrayList<>();
//creating objects of group class
Group swGrp = new Group("Social Welfare", p1);
Group dfGrp = new Group("Drama Fest", p2);
//before deleting drama fest group
System.out.println("List of persons in Drama Fest group:");
for(Person p : p2) {
System.out.println("Person name: " + p.getName() + ", Age:" + p.getAge() + ", Group: Drama Fest");
//deleting drama fest group
dfGrp = null;
//after deleting drama fest group
//person list will not destroy
System.out.println("List of persons after deleting Drama Fest group:");
for(Person p : p2) {
System.out.println("Person name: " + p.getName() + ", Age: " + p.getAge());

Output :
List of persons in Drama Fest group:
Person name: Sam, Age:18, Group: Drama Fest
Person name: Khushi, Age:20, Group: Drama Fest
List of persons after deleting Drama Fest group:
Person name: Sam, Age: 18
Person name: Khushi, Age: 20

Explanation: We can see that the two classes Person and Group are linked together using objects in this example. Social welfare and theatrical festival are the two groups. The person class was used to build these groups. There is a list of people in the group. As seen in the output, we have two people in the Drama Fest group: Sam and Khushi. After that, we destroyed this group by setting group's instance to null. However, despite the group being deleted, our list of people stays undeleted due to the weak association, i.e., aggregation.

17. What is Composition in Java?

There is a significant link between composition and composition. Composition is a term used to describe a part of a larger connection in which a part cannot exist without the whole. Let's look at the relationship between School and Room as an example. There are various rooms in the school item. When the school object is automatically destroyed, all of the room objects are also destroyed, so there is no way for a dependent item to exist without the school object. As a result, these are strongly linked, and this relationship is referred to as composition. When a whole is deleted, all of its pieces are also removed. As a result, the part-of relationship is represented by composition. When two entities come together in a composition, the resulting object cannot exist without the other. As a result, both entities are interdependent in composition.

Example :

import java.util.*;

// activity room class
class ActivityRoom {  
    public String subject;   
    public int id;   
    ActivityRoom(String subject, int id)   
        this.subject = subject;   = id;   
// department class   
class Department {   
private String name;
    //list of activity rooms in a department.   
    private List ar; 
    Department(List ar)  
    {  = ar;  
    // Getting total number of colleges  
    public List getActivityRoomsInDepartment()   
        return ar;   
class Demo {   
    public static void main(String[] args)   
        // Creating the Objects of activity room class.   
     ActivityRoom a1 = new ActivityRoom("Technical", 601);   
     ActivityRoom a2 = new ActivityRoom("Business", 602);   
     ActivityRoom a3 = new ActivityRoom("Economics", 603);  
        // making the list of activity rooms.   
        List act = new ArrayList();   
        // Creating the Object of department class. 
        Department d = new Department(act); 
        // making the list of activity rooms in department.   
        List arlist = d.getActivityRoomsInDepartment();   
        for (ActivityRoom a : arlist) {   
        System.out.println(a.subject + " activity room with id " +;   

Output :
Technical activity room with id 601

Business activity room with id 602
Economics activity room with id 603

Explanation: We have two classes here. Department and activity room A department made up of different activity rooms for different subjects. As a result, if the department is destroyed, all activity rooms within it will be eliminated as well, implying that the activity room cannot exist without the department. It's for this reason that it's called composition.

18. What are the methods in Java?

In Java, a method is a block of code or a set of statements that are put together to perform a certain task or activity. The reusability of code is achieved through the use of a method. A method is created once and then reused multiple times. It also allows for easy code change and readability. Only when we call or invoke a method is it executed. In Java, there are two types of methods: pre-defined and user-defined. Methods that are previously specified in the Java class libraries are referred to as predefined methods. The term "user-defined method" refers to a method that has been written by the user or programmer. User-defined techniques can be tweaked to fit the situation.

19. Explain Static Method in Java?

The static method is a method that has the static keyword in its declaration. In other terms, a static method is a method that belongs to a class rather than an instance of that class. We can also construct a static method by prefixing the method name with the term static. The fundamental advantage of a static method is that it may be called without first generating an object. It can update the values of static data members as well as access them. It is employed in the creation of an instance method. The class name is used to call it. A common example of a static method is the main() method.

Example :

public class Demo  
public static void main(String[] args)   
static void displaymethod()   
System.out.println("It is an example of static method.");  

Output :It is an example of a static method.

20. Explain Abstract Method in Java?

An abstract method is one that is declared with the keyword abstract. There is no implementation, body, or code block for the abstract method. An abstract class must always have an abstract method stated in it, or we might argue that if a class contains an abstract method, it should be declared abstract. If a class has an abstract method, it should be declared abstract; however, the opposite is not true, therefore an abstract class does not need to have an abstract method. In addition, if a regular class extends an abstract class, the regular class must implement all of the abstract parent class's abstract methods or be marked abstract.

Example :

//abstract class area
abstract class Area{
 /* These two are abstract methods, the child class
  * must implement these methods
 public abstract int areaSquare(int s);
 public abstract int areaRectangle(int l, int b);
 //Normal method 
 public void display(){
System.out.println("Normal method in abstract class Area");
//Normal class extends the abstract class
class Demo extends Area{

 /* If we don't provide the implementation of these two methods, the
  * program will throw compilation error.
 public int areaSquare(int s){
return s*s;
 public int areaRectangle(int l, int b){
return l*b;
 public static void main(String args[]){
Area a = new Demo();
System.out.println("Area of square " + a.areaSquare(9));
System.out.println("Area of rectangle " + a.areaRectangle(3,4));

Output :
Area of square 81
Area of rectangle 12
Normal method in abstract class Area

21. Explain Final Method in Java?

A final method is one that has been deemed final. A final method cannot be overridden. This means that the child class can still call the parent class's final method without issue, but it cannot override it. This is because the major purpose of declaring a method final is to prevent the sub-class from changing it.

Example :

class DemoParent{  
final void method(){
System.out.println("Parent class final method");
class Demo extends DemoParent{  
void method(){
System.out.println("final method modified inside child class");
public static void main(String args[]){  
Demo d = new Demo();  

The preceding code will fail because we are attempting to change the last method of the parent class's child class(demo) (demoParent).

22. Explain Equals Method in Java?

In Java,.equals() is a method that compares two objects to see if they are equal. In Java, the.equals() function is used to see if two strings have similar values. It examines them one by one, character by character. The.equals() method should not be confused with the == operator. The String equals() method compares two given strings based on their content, whereas the == operator is used to compare addresses. .equals() returns true if the contents of both strings are identical; otherwise, it returns false. It returns false if none of the characters are matched.

Example :

public class Demo {
    public static void main(String[] args)
        String s1 = "Logicmojo";
        String s2 = "Logicmojo";
        String s3 = new String("Logicmojo");
        System.out.println(s1 == s2); // true
        System.out.println(s1 == s3); // false
        System.out.println(s1.equals(s2)); // true
        System.out.println(s1.equals(s3)); // true

Despite the fact that s1 and s3 have the same field(content), they point to two different objects in memory. As a result, they're at different addresses. As both have comparable material Logicmojo, the == operation returns false and the.equals() method returns true.

23. What do you mean by Message Passing in Java?

In terms of computers, message passing is a phenomena that occurs when processes communicate with one another. In object-oriented programming, it's a type of communication. In Java, message passing is the same as sending an object, i.e., sending a message from one thread to another. It's used when threads don't have shared memory and can't communicate via shared monitors or other shared variables. In message passing, a calling programme sends a message to a process, which then executes its own functionality or code. Message passing is simple to implement, provides better speed, and allows us to create enormous parallel models.
Synchronous and asynchronous are the two types of it.

    🚀 When the objects are running at the same time, synchronous message passing occurs.
    🚀 The receiving object may be down or busy when the asking object sends the message in the case of an asynchronous message passing.

24. Can Polymorphism, Encapsulation and Inheritance work together?

 • When we combine inheritance, polymorphism, and encapsulation to create a programming environment, we get a considerably more robust and scalable programming environment that supports the program-oriented approach. The foundation for reusing the code that we have spent time and effort writing and testing is a well-designed conceptual model of the hierarchy of classes. Encapsulation lets us to change our implementations over time without disrupting the functionality that relies on the public interfaces of our classes. Polymorphism enables us to write code that is legible, tidy, and sensible.
 • When we combine inheritance, polymorphism, and encapsulation to create a programming environment, we get a considerably more robust and scalable programming environment that supports the program-oriented approach. The foundation for reusing the code that we have spent time and effort writing and testing is a well-designed conceptual model of the hierarchy of classes. Encapsulation lets us to change our implementations over time without disrupting the functionality that relies on the public interfaces of our classes. Polymorphism enables us to write code that is legible, tidy, and sensible.
 • Consider the following scenario.
Humans, on the one hand, are a type of heredity, but automobiles are more akin to programmes we develop. To drive various sorts of cars, all drivers rely on inheritance. People interact with features on a variety of vehicles, as there are many distinct sorts of vehicles, each with its own set of features. Engines, brakes, and other mechanisms are implemented through encapsulation, which leads to polymorphism. On the same car, we have a wide range of alternatives for anti-lock braking systems, classic braking systems, and power braking systems. Polymorphism refers to a vehicle that has many braking systems. Encapsulation, inheritance, and polymorphism are all incorporated in this example.

25. What are the Advantages of OOPs Concept?

OOPs ideas are widely acknowledged as one of the most important development methodologies. The following are some of the benefits:

  1. Re-usability : When we talk about re-usability, we mean "write once, use several times," i.e., reusing some facilities rather than having to develop them all over again, which may be accomplished with the help of classes. We can utilise it an unlimited number of times as needed.

  2. Redundancy of data : It is one of the most significant benefits in oops. This is the situation that arises in data storage when the same piece of data is stored in two distinct locations. We may simply build common class definitions for similar features by inheriting them if we wish to apply a similar functionality in several classes.

  3. Code Maintenance : Old code is simple to edit or maintain as new objects that can be developed with minor modifications from the existing ones. It also saves consumers from having to redo work multiple times. It saves time because we adapt old codes to include new updates.

  4. Security : Data hiding and abstraction are used to filter out limiting exposure, ensuring that only relevant data is available for viewing while maintaining security. Benefits of Design

  5. Benefits of Design : Designers will have a longer and more thorough design phase, resulting in better designs. When the programme reaches its critical limits, it will be easier to programme each non-oops one independently.

  6. Troubleshooting is simple : Encapsulation objects are self-constrained when used. So, if developers run across any issues, they can quickly be resolved. There will be no chance of code duplication. Problem-solving flexibility.

26. Differences between Object-Oriented Programming, Procedural Oriented Programming, Structured Programming?

  1. Object-Oriented Programming :
    Object-oriented programming (OOP) is a programming paradigm that organises software design around data, rather than functions and logic. An object is a data field with its own set of properties and behaviour.
    Object-oriented programming (OOP) focuses on the objects that developers desire to handle rather than the logic that is required to manipulate them. This kind of programming is ideally suited to big, complicated, and frequently updated or maintained projects. This encompasses manufacturing and design software, as well as mobile applications; for example, OOP may be used to simulate manufacturing systems.

  2. Procedural Oriented Programming
    Procedural Oriented Programming (POP) is a programming language that takes a step-by-step approach to decomposing a task into a set of variables and routines (or subroutines) using a series of instructions. Each step is completed in a methodical way so that a computer can understand what has to be done.
    It divided into small parts based on the functions and is treated as separate program for individual smaller program.

  3. Structured Programming
    This separates a programme into functions and modules; by using these functions and modules, the programme becomes more legible and intelligible. It emphasises functions above data and concentrates on the development of large software applications.
    Pascal is an example of C.

27. What are the Disadvantages of OOPs Concept?

OOPs ideas are widely acknowledged as one of the most important development methodologies. The following are some of the disadvantages of oops:

  1. Effort : These programmes take a lot of time and effort to develop.

  2. Speed : When compared to other programmes, these programmes are slower.

  3. Size : When compared to other programmes, OOPs programmes are larger.


    1.OOPs is a programming language that uses classes and objects to create a programme.
    2.The core of Java is Object-Oriented Programming (OOPs).
    3.Objects are both instances of classes and real-world entities.
    4.Classes are groupings of items that are written or named using the keyword class.
    5.The four basics of OOP are abstraction, encapsulation, inheritance, and polymorphism.
    6.Polymorphism refers to the existence of many forms that can be overloaded or overridden.
    7.Abstraction refers to the obfuscation of data; it only shows the user the information they need.
    8.The process of obtaining or inheriting properties from one class to another is known as inheritance.
    9.Encapsulation refers to the encapsulation of data using get and set methods.
    10.Reusability, code maintenance, code redundancy, and security are examples of Oops ideas.

Frequently Asked Questions (FAQs)

Java's Object-Oriented Programming (OOP) concepts are essential ideas that direct the creation of software with an object-oriented perspective. By grouping code into objects, which are instances of classes, OOP makes it possible for it to be modular, flexible, and reusable. These ideas are included into Java, an object-oriented programming language, to promote effective and dependable software development. The essential Java OOP ideas are as follows:

1. Classes and Objects: A class is a blueprint or template that outlines the composition and functionality of an object. It contains the attributes and methods that are available to objects of that class. The application's objects, which represent particular things or instances, are instances of classes. They have a distinct condition and behavior.

2. Encapsulation: Encapsulation is the act of grouping data (attributes) and methods into a class, concealing internal information, and making them accessible through clear interfaces. Data abstraction, data integrity preservation, and information hiding—the concealment of internal implementation details—are all made possible by this.

3. Inheritance: Based on pre-existing classes (base classes or superclasses), inheritance enables the development of new classes (derived classes or subclasses). Code reuse and the development of a hierarchical class structure are made possible by the fact that the derived classes inherit the attributes and methods of the base classes. The "is-a" connection, in which a derived class is a tailored variation of the base class, is supported by inheritance.

4. Polymorphism: Through polymorphism, objects of many classes might be seen as belonging to a single superclass. It enables the definition of methods in the superclass and their overriding in the subclasses, offering several implementations depending on the particular object type. Modularity, flexibility, and extensibility of the code are made possible through polymorphism.

5. Abstraction: Within the program, abstraction entails simplification of complex real-world things. It concentrates on outlining crucial traits and actions while omitting superfluous information. Concrete classes can implement common characteristics and methods that are defined in abstract classes and interfaces. In order to manage complexity and write modular, maintainable code, abstraction is helpful.

6. Association, Aggregation, and Composition: As items from one class are related to those from another class, associations between classes express these connections. Specialized types of association include aggregation and composition. Aggregation is a "has-a" relationship in which one class is made up of additional classes, yet the component components are free to exist separately. A stronger type of aggregation is called composition because the components are interdependent and can never exist separately.

7. Overloading and Overriding: Overloading enables the development of numerous methods in a class that share the same name but differ in the number, kind, or arrangement of their parameters. At compilation time, overloading is handled based on the method signature. When a subclass offers a distinct implementation of a method that is already specified in the superclass, however, this is known as overriding. Runtime resolution of method overriding is based on the actual object type.

The foundation for writing modular, reusable, and maintainable code in Java is laid out by these OOP ideas. They support encapsulation, extensibility, reuse, and organization of the code. These ideas can be used by programmers to create robust, scalable, and object-oriented Java software systems.

The four foundational concepts of Java's Object-Oriented Programming (OOP) are:

1. Encapsulation: Encapsulation is the process of grouping data (attributes) and methods into a class and limiting access to an object's internal information. Through clearly defined interfaces, it offers controlled access to the object's state and permits data hiding. Data integrity and security are ensured through encapsulation, which makes sure that internal implementation details are shielded and that they can only be accessed and changed using certain methods.

2. Inheritance: Based on pre-existing classes (base classes or superclasses), inheritance permits the construction of new classes (derived classes or subclasses). The base class's characteristics and methods are passed down to the derived classes, allowing for code reuse and specialization. The "is-a" relationship, hierarchical class organization, and code extension are all supported by inheritance. It encourages code reuse, lessens duplication, and permits the development of class hierarchies.

3. Polymorphism: Polymorphism enables objects of various classes to be handled as though they were members of a single superclass. It gives the option to declare methods in the superclass and implement them differently in the subclasses. By allowing multiple objects to react to the same method invocation based on their unique types, polymorphism promotes flexibility and modularity. It encourages method overriding and method overloading and fosters code flexibility and extension.

4. Abstraction: Within the program, abstraction entails simplification of complex real-world things. It concentrates on outlining crucial traits and actions while omitting superfluous information. Java uses abstract classes and interfaces to implement abstraction. A combination of abstract and concrete methods can be found in abstract classes, which specify a common template. Classes can implement the behavior contracts that are defined by interfaces. Code extensibility, modularity, and concern separation are all aided by abstraction.

The foundation for writing modular, adaptable, and maintainable code is laid out by these four OOP principles in Java. They support separation of concerns, code organization, and code reuse. Java programmers may create reliable, scalable, and object-oriented software systems by utilizing encapsulation, inheritance, polymorphism, and abstraction.

The usage of Object-Oriented Programming (OOP) principles in software development has several advantages and benefits. Here are some main justifications for the usage of OOP concepts:

1. Modularity and Reusability: OOP encourages modularity by enabling the division of software into independent parts known as objects. The code is simpler to comprehend, write, and maintain since objects contain data and related behaviors. Because objects can be used in other areas of the program or in separate programs altogether, modularity makes it possible to reuse code. Existing objects can be reused to speed up development, lessen code duplication, and boost overall productivity.

2. Manageability and Organization of Code: OOP offers a structured method for organizing code. Code becomes more logical and understandable by organizing related data and methods into objects. Having objects that represent actual entities helps the code to be more understandable and readable. This enhances code maintainability since individual objects can be changed or improved without having an impact on the overall codebase. Encapsulation is a concept that OOP also supports because it hides internal implementation details and offers clearly defined interfaces for dealing with objects, further improving the manageability of programs.

3. Abstraction and Complexity Management: A fundamental tenet of OOP, abstraction enables complicated real-world phenomena to be represented within the software as streamlined models. Abstraction obscures superfluous details in favor of emphasizing fundamental traits and actions. By reducing their complexity, software systems become simpler to comprehend and use. Developers may efficiently handle complexity and create scalable and maintainable software by abstracting complicated concepts into manageable and reusable components.

4. Flexibility and Extensibility of Code: OOP encourages extensibility, which enables the addition of new features without changing old code. Code may be easily extended and changed thanks to inheritance, polymorphism, and interfaces. A new class can be created based on an existing one and inherit its characteristics and functions thanks to inheritance. Method invocation is made flexible through polymorphism, which enables objects of many classes to be considered as objects of a single superclass. Classes may implement the contracts that interfaces define, providing for loose coupling and freedom in the design of the code.

5. Collaboration and Teamwork: By offering a shared language and structure, OOP encourages collaborative software development. Objects act as the foundation for independent development by various team members. Through well specified interfaces, objects communicate with one another, promoting teamwork and parallel development. The modular and reusable features of OOP encourage code exchange and collaboration among developers, which boosts output and cuts down on development time.

6. Software Maintenance and Evolution: OOP helps with software maintenance and evolution, which is number six. It is simpler to find problems and correct them because data and behavior are contained within objects. Individual items can be modified or improved without influencing the system as a whole, lowering the possibility of defects or unforeseen effects being introduced. Additionally, the modularity and organization of OOP's code make it simpler to add new features, correct defects, and modify software to meet changing requirements, increasing the product's longevity and maintainability.

In general, OOP concepts are utilized to advance software development procedures, increase the caliber of the code, encourage code reuse, and promote effective teamwork. Developers may build modular, extendable, and maintainable software systems that are simpler to comprehend, change, and scale by applying OOP principles.

The phrase "OOPs concept" is frequently used in interviews to refer to Object-Oriented Programming (OOP) ideas in the context of the programming language under consideration, such as Java, C++, or Python. Due to the widespread use of OOP principles in contemporary software development, interviewers frequently gauge a candidate's comprehension of these ideas.

In an interview, the topic of OOPs principles may come up during questions and talks about the following crucial elements:

1. Encapsulation:

- Knowledge of encapsulation and its advantages, including data concealment, access regulation, and code maintainability.

- Understanding of how to construct encapsulation using getters and setters and access modifiers (public, private, and protected).

2. Inheritance:

- Understanding of inheritance and its functions, such as extensibility, code reuse, and building hierarchical links between classes.

- Being aware of the relationships between superclasses (base classes) and subclasses (derived classes).

- Understanding of how to use "extends" and "implements" keywords in programming languages to implement inheritance.

3. Polymorphism:

- Understanding polymorphism and its importance in OOP, particularly method overloading and overriding, is step three.

- Experience with dynamic method dispatch and inheritance-based runtime polymorphism.

- The ability to tell runtime polymorphism (method overriding) apart from compile-time polymorphism (method overloading).

4. Abstraction:

- Understanding the notion of abstraction and how it works to represent important qualities in complicated systems in order to simplify them.

- Understanding of how to achieve abstraction using abstract classes, interfaces, and use cases.

- Understanding how abstraction promotes code modularity, concern separation, and support for future changes.

5. Composition, Association, and Aggregation:

- A working knowledge of class relationships such as association, aggregation, and composition.

- Recognizing the variations between these connections and their corresponding modeling applications.

6. SOLID Principles:

- Knowing the SOLID principles—Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion—and how to apply them to software architecture.

- Understanding the role that SOLID principles play in the extensibility, flexibility, and maintainability of code.

You can be asked in an interview to clarify these ideas, give coding examples, use OOP to address programming issues, or talk about the benefits and drawbacks of adopting OOP in software development. These OOPs ideas are fundamental to object-oriented programming and are utilized frequently in industry-standard software development processes, hence it is essential to have a firm grasp on them.

Because it was created from the ground up to accept and apply OOP's ideas, Java is frequently referred to as an OOP language. These justifications are why Java is referred to as an OOP language:

1. OOP Design Philosophy: OOP ideas, which offer a modular and structured approach to software development, were heavily emphasized when Java was developed. By adhering to OOP design concepts, the Java language's creators tried to make it simple and intuitive to use.

2. Object-Oriented Features: Java has essential OOP elements including abstraction, polymorphism, inheritance, and encapsulation. Developers can write modular, reusable, and maintainable code thanks to these characteristics.

3. Class and Object Model: Everything in Java is an object, with the class serving as its fundamental building block. The qualities and functions of an object are defined by its class, which serves as a blueprint for building new objects. The object-oriented paradigm is compatible with Java's class-based design.

4. Encapsulation and Information Hiding: Encapsulation is supported by Java and allows for data hiding as well as the protection of implementation details from outside code. Access modifiers (public, private, and protected) are used to limit class members' visibility while promoting information hiding and encapsulation.

5. Inheritance and Polymorphism: Java enables the development of class hierarchies through inheritance, where derived classes acquire traits and characteristics from their base classes. Code reuse, extensibility, and the creation of "is-a" relationships are all made possible through inheritance. Java supports polymorphism, another essential OOP concept, through method overloading and overriding.

6. Abstraction and Interfaces: Java's abstract classes and interfaces operate as abstraction-supporting techniques. Subclasses can be built on top of abstract classes, which can define abstract methods. In order to support code modularity and multiple inheritance-like behavior, interfaces create contracts that classes can implement.

7. OOP Advantages and Best Practices: Java promotes OOP concepts, which provide a number of advantages including code reuse, modularity, maintainability, and flexibility. Java supports best practices in software development by embracing OOP, which makes it simpler to construct scalable and reliable programs.

Java is a popular choice for creating object-oriented software due to its strict adherence to OOP concepts and extensive built-in feature and library set. Its emphasis on encapsulation, inheritance, polymorphism, and abstraction is in line with the fundamental principles of OOP, which helps to explain why people refer to it as an OOP language.

Although Java is frequently regarded as an object-oriented programming (OOP) language, it is not completely 100% OOP. Although Java places a significant emphasis on OOP principles and offers a wide range of OOP concept support, there are some features that stray from strictly object-oriented design. Here are some things to think about:

1. Primitive Data Types: Java has primitive data types that are not objects, such as int, double, boolean, etc. These primitive types have no common superclass and are not members of the object hierarchy. Java does, however, offer wrapper classes (such as Integer, Double, and Boolean) that encase primitive types and enable their treatment as objects when required.

2. Static Members and Methods: Java permits classes to declare static members and methods. Individual objects are not the owners of static members; rather, the class itself is. They are reachable without making a class instance. As opposed to pure OOP's instance-based design, static members lack object-specific state and behavior.

3. Procedural Programming: Java enables procedural programming in addition to OOP. Java permits the declaration of "helper methods," or static methods that can be accessed without constructing objects, outside of classes. These methods perform useful tasks and can be applied in a procedural programming manner without strictly following OOP guidelines.

4. Libraries and APIs: Non-OOP components can be found in Java's standard libraries and APIs. For instance, the Java I/O library has classes and methods that work procedurally with files and streams. Although these libraries still conform to the general structure and syntax of the Java language, they do not always fully follow OOP concepts.

Despite these variations, it's crucial to remember that Java was primarily created as an object-oriented language and that it strongly encourages the adoption of OOP principles.

Inheritance, polymorphism, encapsulation, and abstraction are used primarily in Java programming to create and manipulate objects. The vast majority of Java programs are created utilizing object-oriented design patterns and best practices, which take advantage of OOP's advantages.

Java's combination of OOP and procedural programming elements offers flexibility and enables developers to select the best method for a particular task. The availability of non-OOP features in Java makes it easier to integrate different programming paradigms, be compatible with legacy code, and improve performance in particular situations.

As a result of its substantial support for OOP concepts, design patterns, and the widespread application of object-oriented programming techniques in Java development, Java is often considered as an object-oriented programming language even if it is not precisely 100% object-oriented.

An overview of the main ideas, tenets, and advantages of object-oriented programming is given in Introduction to Object-Oriented Programming (OOP). It acts as a foundation for comprehending the essential ideas that direct object-oriented software development. A thorough description of OOP's inception is provided below:

1. Paradigm Shift: By moving away from procedural programming and emphasizing the organization of code around objects, OOP marks a paradigm shift in software development. It places a focus on using objects to represent actual people, things, or ideas, making it possible to develop software in a more logical and modular way.

2. Objects and Classes: In OOP, objects serve as the fundamental building blocks for instances of classes. A class serves as a blueprint or model for the structure and behavior of things. Complex systems are easier to understand and modify when data (attributes) and action (methods) relating to a particular item or concept are encapsulated in objects.

3. Encapsulation: A fundamental OOP principle that encourages data hiding and abstraction is encapsulation. The internal state of objects is protected from direct external access by bundling data and related methods within a class. By ensuring that data is accessed and modified through well specified interfaces, encapsulation improves the security, maintainability, and reuse of programs.

4. Inheritance: Based on pre-existing classes (superclasses), inheritance enables the development of new classes (subclasses). Subclasses can reuse code, be extended, and establish hierarchical relationships by inheriting properties and methods from their superclasses. The "is-a" connection, in which a subclass is a customized version of its superclass, is supported via inheritance.

5. Polymorphism: Through polymorphism, objects of many classes might be seen as belonging to a single superclass. It enables the definition of methods in the superclass and their overriding in the subclasses, offering several implementations depending on the particular object type. Because polymorphism allows objects to react differently to the same method invocation, it encourages the flexibility, extensibility, and modular architecture of programming.

6. Abstraction: Within the program, abstraction entails simplification of complex real-world things. It concentrates on outlining crucial traits and actions while omitting superfluous information. To achieve abstraction, abstract classes and interfaces are employed. In contrast to interfaces, which provide contracts that classes can implement, abstract classes offer a common template for subclasses. Code abstraction improves modularity, maintainability, and concern separation.

7. OOP's advantages: OOP has a number of advantages, including modularity, maintainability, scalability, and code reuse. OOP enables the creation of modular, reusable components that are simple to comprehend, modify, and extend by structuring code around objects. Code organization, the separation of concerns, and the capacity to respond to changing requirements are all facilitated by OOP's emphasis on encapsulation, inheritance, polymorphism, and abstraction.

Software engineers can more efficiently design and create large systems by using an object-oriented approach, which produces code that is simpler to comprehend, maintain, and extend. The powerful collection of rules and ideas offered by OOP make it easier to organize, reuse, and scale code, which in turn makes software systems more effective and reliable.

A crucial aspect of object-oriented programming in Java is inheritance, which enables classes to take on traits and characteristics from other classes. In Java, there are various types of inheritance, each with a distinct function. The principal inheritance kinds are as follows:

1. Single Inheritance: The simplest type of inheritance is single inheritance, in which a class derives from a single superclass. In this kind of inheritance, a subclass extends just one superclass and takes on all of its traits. Single inheritance encourages code reuse and makes it possible to build a straightforward class hierarchy.

2. Multiple Inheritance (Not supported in Java): A class can inherit from many superclasses in a condition known as multiple inheritance, which Java does not support. Java does not explicitly enable multiple inheritance, although C++ and other computer languages do. This is due to the fact that multiple inheritance can result in complexity and disputes known as the "diamond problem." Java offers interfaces, which let a class implement several interfaces while deriving from a single superclass, to provide equivalent capabilities.

3. Multilevel Inheritance: Multilevel inheritance refers to a hierarchy of classes connected by inheritance. A class acts as the superclass for another class in this sort of inheritance, and that class in turn serves as the superclass for still another class, and so on. Each subclass propagates the inheritance chain by receiving traits and actions from its immediate superclass.

4. Hierarchical Inheritance: Multiple subclasses can inherit from a single superclass in a hierarchy, which is known as inheritance. A superclass acts as the foundation class for a number of subclasses under this sort of inheritance, each with its own unique characteristics and behaviors. While maintaining their own distinctive qualities, the subclasses have common traits that were inherited from the superclass.

5. Hybrid (Multipath) Inheritance (Not supported in Java): Hybrid (Multipath) inheritance combines various inheritance types, such as multiple inheritance and multilevel inheritance. Java does not, however, natively implement hybrid inheritance to prevent issues and ambiguity in method resolution. Java instead offers interfaces as a way to create behavior similar to multiple inheritance.

A balance between maintainability and code simplicity is provided by Java's capability for single inheritance and interfaces. Interfaces enable code reuse and flexibility without the complications of multiple inheritance by allowing classes to implement numerous interfaces.

It's vital to remember that good design and adherence to object-oriented programming concepts, including the Liskov substitution principle and avoiding extensive inheritance hierarchies, should be taken into consideration while employing inheritance. A clear and intelligible class structure is promoted while code reuse, extensibility, and modularity are improved by the proper use of inheritance.

A major concept in object-oriented programming (OOP) is polymorphism, which enables objects of several classes to be viewed as belonging to a single superclass.

It allows for the representation of numerous linked items via a single interface, allowing for flexibility and extensibility in the architecture of the code. Depending on their unique types, many objects can respond differently to the same method call thanks to polymorphism. The main features of polymorphism are as follows:

1. Method Overriding: A subclass might provide a new implementation for a method that is already declared in its superclass to achieve polymorphism. The name, return type, and parameters of the superclass function are shared by the overridden method in the subclass. The specific method to be called is chosen at runtime based on the type of the object.

2. Dynamic Method Dispatch: Dynamic method dispatch is a feature of polymorphism in Java, where the choice of which override method to call is chosen at runtime based on the type of the real object. As a result, different objects can display various behaviors in response to the same method call, increasing the flexibility and adaptability of the code.

3. Upcasting and downcasting: Upcasting and downcasting are also a part of polymorphism. An object of a subclass is treated as an object of its superclass through the process of upcasting. There is no need for any explicit casting because it is implicit. Upcasting enables polymorphic behavior since it enables the same method to be called on objects belonging to several subclasses via a reference to the superclass.

On the other hand, downcasting refers to the practice of considering an object belonging to a superclass as an object belonging to its subclass. If the object being downcast is not an instance of the target subclass, a ClassCastException may occur, necessitating explicit casting, hence it should be used with caution.

4. Method Overloading: Unrelated to polymorphism, method overloading is another Java feature that enables the implementation of numerous methods with the same name but distinct parameter lists within the same class. This kind of polymorphism is compile-time polymorphism. The number, nature, and order of the parameters determine how overloaded methods are resolved at compile time, not the runtime type of the object.

OOP polymorphism has a number of advantages, such as:

- Flexibility and extensibility of the code: Polymorphism makes it possible to introduce new subclasses without changing the code that already exists. In order to promote code reuse and modularity, new subclasses might be considered as objects of the superclass.

- Code Abstraction: By enabling the treatment of objects at a higher level of abstraction, polymorphism facilitates abstraction. As a result, code modularity and the separation of concerns are encouraged by the ability to conceal the precise implementation details of objects.

- Code Readability and Maintainability: Polymorphism makes it possible to handle objects with comparable behaviors consistently, which enhances code readability. As modifications made to the superclass or overridden methods are automatically reflected in all subclasses, it improves code maintainability.

In object-oriented programming, polymorphism is essential for obtaining code flexibility, modularity, and extensibility. Utilizing the strength of inheritance and method overriding, it enables the development of reliable and flexible software systems.

Encapsulation in Java is a fundamental concept in Object-Oriented Programming (OOP) that includes combining data (attributes) and related methods (behaviors) within a class and controlling access to them. It offers a means to safeguard an object's internal state by limiting access to and modification of data to predefined interfaces. Encapsulation encourages data hiding, modularity, and maintainability in programs. The main components of encapsulation are as follows:

1. Data Hiding: Encapsulation enables the external world to be shielded from an object's internal implementation details. Class members (attributes and methods) are made inaccessible to outsiders by being declared as private. This promotes data integrity and security by preventing unauthorized access to and modification of data.

2. Access Modifiers: Java offers access modifiers that let you manage the visibility and accessibility of class members. In Java, there are three primary access modifiers:

- Private: A member with the private modifier can only be accessed by other members of the same class; it is inaccessible to outsiders.

- Public: The member can be accessed without restriction from any class or package thanks to the public modifier.

- Protected: Access to a member within the same class, its subclasses, and the same package is permitted by the protected modifier.

3. Getters and Setters: To provide for controlled access to private properties, encapsulation promotes the use of getter and setter methods. In contrast to setters, which are public methods that allow private attribute values to be changed, getters are public methods that allow getting the values of private attributes. Getters and setters offer a way to interact with an object's state while also guaranteeing that the data is legitimate and properly encapsulated.

4. Data Validation and Consistency: By using encapsulation, setter methods can implement data validation logic. Encapsulation enables developers to impose business rules and uphold data consistency by enclosing data and offering controlled access. Data validation makes sure that only suitable and legitimate values are applied to attributes, improving the code's accuracy and dependability.

5. Code Maintainability: By encapsulating an object's implementation information, encapsulation helps to maintain the code. An object's internal behavior and structure can be changed without having any impact on the external code that communicates with it. The impact of alterations on other areas of the codebase is minimized because changes made within the class are limited to the class itself. This makes it simpler to debug, refactor, and improve the code.

6. Code Reusability: By encapsulating related data and behavior inside a class, encapsulation encourages code reusability. The same object can be utilized repeatedly inside the same application or across many programs. The encapsulated class can be used as a module or component in a variety of settings by offering a clear interface through getters and setters, which enhances the structure and effectiveness of the code.

A key component of OOP is encapsulation, which offers a framework for data hiding, access control, and code modularity. Java programmers can write more safe, reusable, and maintainable code by encapsulating data and associated behaviors. Encapsulation makes it possible to clearly separate an object's internal implementation details from its outward usage, making software systems more durable and scalable.

The first programming language created exclusively for Object-Oriented Programming (OOP) is widely regarded as "Simula," which was developed in the late 1960s by Ole-Johan Dahl and Kristen Nygaard at the Norwegian Computing Center in Oslo. Simula set the stage for other OOP languages by introducing the fundamental OOP ideas.

Initially, the purpose of Simula was to facilitate the simulation of real-world systems, particularly discrete-event simulation-based systems. The fundamental OOP building blocks of classes and objects were introduced by the language. It permitted the definition of classes that contained data (attributes) and behavior (methods), as well as the construction of objects from these class definitions.

Simula introduced a number of essential ideas that are now included in all modern OOP languages, including:

1. Classes and Objects: Simula introduced the idea of classes, which serve as the building blocks for making things. Classes, which contain characteristics and methods, determine the composition and operation of objects. Objects are instances of classes that represent concepts or real-world objects.

2. Inheritance: Simula introduced the idea of inheritance, which made it possible to build new classes off of older ones. As a result of inheritance, which encourages code reuse, extension, and the formation of hierarchical relationships, subclasses can inherit attributes and functions from their superclasses.

3. Dynamic Dispatch: Dynamic dispatch, which Simula introduced, refers to the capability to choose the best implementation of a method at runtime based on the actual type of the object, was previously only available in Simula. This is a key feature of polymorphism that enables objects of several classes to react in various ways to the same method call.

Simula had a significant impact on later programming languages that adopted OOP, such as Smalltalk, C++, and Java. The OOP paradigm was further popularized by Smalltalk, which was created in the 1970s. It also introduced the idea of a full-featured integrated development environment (IDE). The procedural programming language C and OOP characteristics were combined in the 1980s to create C++, a highly adaptable and popular computer language. With the introduction of Java in the middle of the 1990s, OOP was able to appeal to a wider audience.

It should be mentioned that while Simula was the first language specifically created for OOP, other languages like Lisp and ALGOL had early implementations of several OOP ideas. Simula, however, stands out as the innovator who built a thorough set of OOP ideas and laid the groundwork for other OOP languages.

Java uses the term "multithreading" to describe a program's capacity to run many threads simultaneously. A thread is a compact unit of execution that stands in for a distinct control flow within a program. A Java program can execute numerous tasks at once by using multiple threads, which increases its efficiency and responsiveness.

The main features of multithreading in Java are as follows:

1. Thread Creation: The first step in creating a thread in Java is to extend the Thread class or implement the Runnable interface. The Runnable interface defines a task that can be executed by a thread, whereas the Thread class offers methods for managing a thread's lifespan. By starting a new thread, the program can handle several tasks at once.

2. Thread Scheduling and Execution: The Java thread scheduler controls how threads are run on the underlying operating system. Each thread is given time slices or priorities by the scheduler, enabling what seems to be parallel execution. Thread priority and the actions of the underlying operating system are just two of the many variables that might affect the execution order of threads.

3. Synchronization and Inter-thread Communication: The challenge of managing shared resources and preventing conflicts between threads is introduced by multithreading. To maintain thread safety and avoid data corruption, Java offers synchronization mechanisms including synchronized blocks and methods, as well as atomic variables and locks. Through techniques like wait(), notify(), and notifyAll() methods, inter-thread communication can be established, allowing threads to coordinate their tasks and communicate data.

4. Benefits of Multithreading: The advantages of multithreading In Java programming, multithreading has the following advantages:

- Better Performance: Multithreading enables concurrent task execution, enabling effective system resource use and quicker program execution.

- Responsiveness: By enabling concurrent processing and ensuring that the user interface remains interactive even during resource-intensive activities, multithreading improves the responsiveness of Java programs.

- Parallelism: On multi-core processors, multithreading enables parallel task execution, utilizing the available processing capacity to speed up program execution.

- Modularity and Code Organization: Multithreading enables programmers to modularize their code by allocating particular tasks to several threads, which improves the program's maintainability and organization.

5. Thread States and Lifecycle: Java threads experience a variety of states throughout their lifetime, including:

- New: Although the topic has been begun, it has not yet been created.

- Runnable: The thread is qualified to execute, but depending on the thread scheduler, it may or may not be doing so right now.

- Blocked: The thread is stalled due to a synchronization mechanism or is awaiting a resource.

- Waiting: The thread is awaiting the fulfillment of a particular condition.

- Terminated: The thread's execution has come to an end or has been stopped.

6. Thread Safety and Concurrent Programming: Multithreading creates problems with thread safety and concurrent programming. To prevent problems like race situations, deadlocks, and inconsistent data, proper synchronization, thread-safe data structures, and careful handling of shared resources are essential.

Java offers a comprehensive collection of tools and APIs to make multithreaded programming easier. Java.lang is used.the Java.lang thread class.Some of the key elements for using multithreading in Java include the runnable interface, synchronization methods, and concurrent data structures in the java.util.concurrent package.


1. In Java, which of the following is not an OOPS concept?

2. When do you know if a method is overloaded?

3.Is Abstraction Java notion allows you to turn real-world objects into classes?

4. By merging methods and attributes into a class, which Java concept is achieved?

5.When an item has its own lifecycle but no owner, what is it called?

6. What is the name of the situation in which a child object is killed if the parent object is killed?

7. Is method overriding a blend of polymorphism and inheritance?

8. What is the name of the situation in which each object has its own lifecycle and no child object can be related to another parent object?

9. Polymorphism in Java is defined as which of the following?

10. Which of the following characteristics does not appear in the broad definition of OOPS?

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