OOPS in Java || Java and DSA course || Blog 15

-

OOPS stands for object oriented programming system. OOPS is common in every programming language whether it is c++ or java.

Modern languages are based on oops.

for a quick overview , we will be learning ;

  • constructors
  • Polymorphism
  • Inheritance
  • Access Modifiers
  • Encapsulation
  • Abstraction

what is an object and classes?

Everything in Java is associated with classes and objects, along with its attributes and methods.

A Class is like an object constructor, or a "blueprint" for creating objects. 

lets take a student. Here, a student is an object while attributes like name, age, section is object attributes/classes.

the functions inside the classes are called members.

 

  in the line Student student1 = new Student();

new stands for the memory allocation

Student() is a special type of function called Constructors.

Constructors

constructors construct objects. They cannot return .Their name should be same in the class . It calls only one time.

there are 3 types of constructors:

  • Non parameterized
  • Parameterized
  • Copy constructors.

the student example we saw just now was an example of Non parameterized. we didn't pass any  parameter inside the brackets.

Parameterized


 Copy Constructors

these constructors copies someone else's data and prints it to us.


if we have constructors, we must haev destructors right!

well in java, we have our own garbage collector/destructors. it deletes stuff which is not used.

Polymorphism

it is made of 2 words. poly and morphism . poly means many, morphism means forms.

it means that we create many functions but it means the same.

lets take example as a car:

polymorphism works only when   parameters are differewnt(int, string, boolean) or when types are different(void, int, return) or add parameters like car1.print(car1.name, car1.mileage);

there are two types of polymorphism, oveloading and overriding.

over loading is of compile type, it gives error while writing program, over riding gives error while running program.over riding is used a bit less because of this.

Inheritance  

it passes properties from one class to another class

it stands for reusability, lets say you are making a website which has 4 buttons. they should be off same size. are we going to write them again and agian??NO. instead we are going to use Inheritance.

here another class takes all the attributes used in the class

 here, btn1 can access both sizee() which is in the button function and printname().

 there are 4 levels of Inheritance. what we saw here was single level inheritance.

 


 

Packages

Everyone likes clean house, where everything is at its place. just like that, we should also keep our programs clean so that if someones reading it, he/she will not get confuse. package works just like that. imagine it as a pecil case , where you keep all your pen and pencils.

packages are Built-in and user-defined.built in for example is java.uitl.*;

user defined packages are made by us.

simply write package package name;

then use import name.*; in other files to use the package.

Access Modifiers

it is used to define a boundary between who can red the data and who cant.

we have been using public for a long time.it is one type of access modifiers.

  1. Public - anyone can get it/ packages can get it.
  2. Private - only inside class
  3. Protected - in packages and in all files where package is importes
  4. default - It can be accessed from within the class, outside the class, within the package and outside the package.

Encapsulation- it is combining data and functions in the whole class.

Abstraction

two types

  • abstract keyword
  • interfaces

Data abstraction is the process of hiding certain details and showing only essential information to the user.

you cannot make an object of abstract class

abstract class hello{
public abstract void sec();
// Regular method
public void what() {
System.out.println("secret");
}

}

class Run extends hello{
public void sec() {
// The body of animalSound() is provided here
System.out.println("The pig says: wee wee");
}

public static void main(String[] args){
Run running = new Run();
running.what();
}}

 

it will run the pig says: wee wee  /n secret

here we didn't knew what was in the what() but it ran.

 

Interfaces

An abstract class contains an abstract keyword on the declaration whereas an Interface is a sketch that is used to implement a class.

interface shape{

....

} 

class button implements animal{

.....

}

 

 

 

Comments

Post a Comment

Popular posts from this blog

LinkedList Problems for Beginners DSA || Java and DSA course || Blog 17

-
Image
Linked lists are fundamental data structures in computer science, offering a dynamic and flexible way to organize and manipulate data. In this blog post, we'll dive into several common linked list problems and provide clear, step-by-step solutions using Java. Whether you're preparing for technical interviews or enhancing your data structures skills, understanding how to navigate and manipulate linked lists is crucial.   We'll explore five key linked list problems and present efficient Java implementations for each:   Question 1: Problem Statement: Given a singly linked list, remove the nth node from the end of the list and return the resulting linked list. We are provided with the head of the linked list and an integer 'n,' where 1 ≤ n ≤ length of the linked list. Example 1: Input: [1,2,3,4,5], n = 2 Output: [1,2,3,5] Explanation: In the given linked list, removing the second node from the end results in the modified list [1,2,3,5]. Example 2 : Input: [1], n = 1 ...
Read more

Introduction to Java || Java + DSA course || Blog 1

-
Image
What is y our mother tongue? It can be Eng lish, Hindi, Ja pa nes e, R ussian....m any more . There are total 7000 Languages across the world for us to Communicate. But what if we want to talk to a computer? Of course computer doesn't understand English. So what does it understand? Computer understands a simple language called as Binary . Its script contains only 0s and 1s.It seems easy to learn but it isn't. Just to write A in binary is 01000001 . So even if we just want to do a simple thing like adding 2 numbers, it will mostly be hard enough.   Due to these issue, high level languages were invented. What are they? Think of it as a mixture of human language and computer language. Due to these languages humans could command a task to the computer easily. One of the best and easy High level languages is Java Java is the language which can be run on any computer having JDK.(java development kit.We will talk about it in our 2nd blog)  Lets talk about how do we give a comman...
Read more

LinkedList in DSA || Java and DSA course || Blog 16

-
Image
I n simple words, a collection which can contain many objects of the same type, like the ArrayList is a LinkedList. Arraylist uses dynamic array. Lets say we take an array size of 5. we gave input as 1,2,3,4,5. Now, if we gave it one more value, It creates a new arraylist of sizex2 = 5x2 = 10. it copies data from the first arraylist and then appends the new value. if something is removed between the arraylist, every value shifts one by one. Same is with the insert. From this, we can say that arraylist is better for storing values instead of manipulating it. So what is the difference between ArrayList and LinkedList? In this blog we will take a look into Singular LinkedList and code related to it. For a quick overview, contents are, What is LinkedList? Difference between arraylist and linkedlist Creating Node class Add Node at beginning Extend a node Delete first node Delete last node What is LinkedList? LinkedList is nothing but nodes connected to each other. A node is a point ...
Read more