DEV Community: Atharva Siddhabhatti

Java 8 Collection Framework: List

Atharva Siddhabhatti — Thu, 28 Apr 2022 16:54:30 +0000

The List is one of the interfaces of the collection which extends the collection and declares the behavior that stores a group of elements. List is kind of an array which stores the elements and which can be inserted of accessed by their index position in the list. The index starts from 0.

interface List
E is the type of object which the list will hold. List also has its own methods defined. Some methods can throw different kind of Exceptions. If we try to save null object in the list then NullPointerException Will be thrown as null elements are not allowed in the list.

There are Many methods which are supported by the list:-

The void add(int index,E) adds the element at a specified index position in the list.
boolean addAll(int index,Collection) adds the group if element starting from the given index position. Returns true if the list is changed otherwise will return false.

To get the object stored at a particular index the get(index) method is used.
The int indexOf(Object obj) returns the index of that particular object.
For all versions, null elements are not allowed. In all cases, the List implementation is unspecified.

Click Run below code to see some of the methods running:-

In the next blog we will see Set Interface.

Reference Links of the series:-
1) Collection Framework Introduction

Java 8 Collection Framework: Introduction

Atharva Siddhabhatti — Mon, 17 Jan 2022 07:55:58 +0000

Collection Framework is used to handle the group of objects of a program. The Collection Framework provides different implementation of interfaces such as LinkedList, HashSet, TreeSet. Also standard Array is also a part of this framework. Collection Framework also has one interface called as Iterator. The iterator is used to enumerate the content of a collection. Following are the List of Collection interface provided by the framework:-

Array
LinkedList
HashSet
TreeSet
Map
Deque
List
NavigableSet
Queue
Set
SortedSet

These collection uses Comparator, RandomAccess, Iterator, ListIterator and Spliterator.

Compartor is used to compare two objects

The Iterators are used to enumerate the object within the collection

In addition to this there are optional methods, Optional methods are used to modify the content of the collection.

Collection is a generic interface

interface Collection

E is the type of object that particular collection can hold.

Methods in Collection interface:-

In the next post we will see each of the Collection provided in the Framework with their examples.

How to setup React Native Development Environment for Android development on windows

Atharva Siddhabhatti — Tue, 02 Nov 2021 17:53:12 +0000

React Native is an open-source UI software framework created by Facebook, Inc. It is used to develop applications for Android, Android TV, iOS, macOS, tvOS, Web, Windows and UWP by enabling developers to use the React framework along with native platform capabilities. - Wikipedia

Software Required and their Links:-
Download all these software so that it will be an easy step wise process to install them one by one.

Download latest version of Node:- CLICK HERE
Download Java if not preinstalled on the system:- CLICK HERE
Download Android Studio:- CLICK HERE

Let's Start, follow all the steps carefully otherwise you may face errors

Install Node

Download the latest version of node and install it. Open the exe file and follow the steps shown in the installation wizard.

Once the installation is finished check if it successfully installed or not by running following command in cmd.

node --version

If you see the version as it is shown in the picture then node is installed successfully. CONGO. Still long way to go....

Install Android Studio

Download the android studio setup exe from the above link and install it as follows
Download the exe file from here link given above

Click Next

Don't change any components setting let it be default and click next. if Android Virtual Device is not selected then select it.

Let the installation finish

WOHOO! You have successfully installed the Android studio. Select Start android studio and click on finished.

Click Next

Select standard installation type and click next.

Verify the installation directory and click on finish

It will download and install all the required sdk's.

Installing SDK

After the Android Studio is started Click on More Action -> SDK Manager

Check Android 10.0(Q) or whichever version of android you want the app to be compatible with. Android has backward compatibility that means the app will work on the older version of android look for android docs for more details.

Choose SDK Tool tab and see if the following components are installed some tools may differ depending on the system. Important one is the Android Emulator.

After this click on Apply and Accept all the licenses and let the installation finish.

Install Android Emulator

Click on the AVD Manager to install Virtual Android Emulator

Click on Create Virtual Device

On the next screen select the device you want to install. You can choose any.

On the next screen select the SDK you installed in the previous step.

Verify the details if you want to change the name you can do that as well after verifying click on finish and let the download and installation finish. It might take some time depending on the speed of the internet.

Configure the ANDROID_HOME environment variable

The React Native tools require some environment variables to be set up in order to build apps with native code.

1.Open the Windows Control Panel.
2.Click on User Accounts, then click User Accounts again
3.Click on Change my environment variables
4.Click on New... to create a new ANDROID_HOME user variable that points to the path to your Android SDK:
OR
On search box type env and select the edit environment variable option.

In the user variable section click on new and add the details as below change the directory of SDK depending on where you have installed the SDK.

Click OK and select Path from the section and click on new. Add the platform-tool directory as below. It might be different depending on where you have installed you SDK's.

CONGRATULATIONS!!!!! You have successfully installed React native. In the next blog we will see how to make our first program in react native and run it on a virtual emulator.

If you are facing any issues or error do write them in comment I will be happy to help. Thank You.

Strings in Java

Atharva Siddhabhatti — Thu, 28 Oct 2021 10:08:26 +0000

As other languages, String in java is also a sequence of characters. But java does not implement string as an array of character rather it considers it as a complete object of type string.

How to create a string object using new keyword and literals

There are two ways in which we can create a string object, by using new keyword or by using literals. Literal representation means literally representing the value of it like integer, string. Below code represents how we can create a string using new keyword.

String a = new String();

As we know, new keyword is used to create the instance of that class. Above we have created an instance ‘a’ of a type string with no characters. To create a string with a value in it then you can do that like this.

char name[] = {‘x’,’y’,’z’}
String a = new String(chars);

Above we have created an character array name[] with values ‘x’, ‘y’, ‘z’ and then we allocated that complete array to the string ‘a’. We have used the constructor of String class to initialize the value of the string.

As we have seen above, it is little confusing and lengthy to create a string using new keyword. But there is a really easy way to that and this is where the literals come to save us.

String s = “xyz”;

This is how we create the string in java using literals. For every string literal in program, Java automatically constructs a String object with the initial value provided to it. You can use a string literal any place in you program to create a string object of it.

String Example

Let’s write a simple hello world program.

public class HelloWorld {
    public static void main(String args[]) {

        String s1 = new String("Hello World using new keyword"); // Using new keyword
        String s2 = "Hello World using literals";

        System.out.println(s1);
        System.out.println(s2);
}
}

Run Code From here:- CLICK HERE

CodeChef - Sum Of Digits Of a Number

Atharva Siddhabhatti — Fri, 22 Oct 2021 14:45:42 +0000

Problem Code:- FLOW006

Problem Statement:- You're given an integer N. Write a program to calculate the sum of all the digits of N.

Input

The first line contains an integer T, the total number of testcases. Then follow T lines, each line contains an integer N.

Output

For each test case, calculate the sum of digits of N, and display it in a new line.

Explanation

As said in the problem statement, we have to find the sum of all the digits of a number. For Example:- 321 will be 3+2+1 = 6.

For this we use basic math rule which is of division when we do the 10 modulo of any number we get the last digit of that number as the output, using this principle we get the last digit of 321 number which is 1. After that we divide n by 10 which will be 321/10 = 32.1 but as we have declared n as integer the value taken by the complier will be 32 and we save 32 in n. After that we repeat the above steps until the value of n becomes 0 and in last we print the sum. The below code explains it.

In each program we take T as a Test cases so that we can supply multiple input to the program in a single run and get the output for all of them in one step rather than running the program multiple times for each input. Basic for loop is used for this purpose.

while(n!=0) {
            sum = sum+n%10;
            n=n/10;
        }
        System.out.println(sum);

Input:

Output:

6
13
28

Link to original problem https://www.codechef.com/problems/FLOW006

Run the program from here:- Click Here

Add input in Stdin Inputs

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Codechef - Professor And Directions

Atharva Siddhabhatti — Wed, 20 Oct 2021 23:23:12 +0000

Problem Code: DIRECTN

The Professor is facing the North. Tokyo is in trouble, and she is facing the South. Professor being her guardian angel wants to help her.

So, The Professor will follow some instructions, given as a string S of length N, and will turn either left or right according to these instructions. He can save Tokyo only if after following a substring of instructions he will face in the same direction that Tokyo is facing.

Will the Professor be able to save Tokyo?

Input

The first line contains an integer T denoting the number of test cases. The T test cases then follow.
The first line of each test case contains N.
The second line contains a string that contains only 'L' and 'R', where 'L' represents left and 'R' represents right.

Output

For each test case, output "YES" if the Professor will be able to save Tokyo and "NO" otherwise.

Output is case insensitive, which means that "yes", "Yes", "YEs", "no", "nO" - all such strings will be acceptable.

Explanation

The Professor he first Facing in the North side goal is to save Tokyo, Tokyo will be saved only if professor is facing south after following instructions. The instructions contains letter 'L' for Left and 'R' for Right. We have defined two function namely twoLeft and twoRight which is checking if the L or R letter consecutively appered in the string for 2 or more than two times. If that is the case rotating in same direction twice will lead to be facing the opposite direction the person is standing in this case the professor was standing in North Direction.

After getting the number of consecutive 'L' or 'R' . The next condition checks if the count is 2 or greater than 2 if it is true than YES is printed otherwise No will be printed and Professor will not be able to save Tokyo.

Condtion to check if 'L' or 'R' count is equal to or greater than 2.

            int max = twoRight(str);
            int max1 = twoLeft(str);
            if(max >= 2 || max1 >=2) {
                System.out.println("YES");
            }else {

                System.out.println("NO");
            }

Check number of lefts and number or rights

private static int twoRight(String str) {
        int max = 0;
        for (int i = 0; i < str.length(); i++) {
            int count = 0;
            for (int j = i; j < str.length(); j++) {
                if (str.charAt(i) == str.charAt(j)) {
                    if(str.charAt(i)=='R'){
                        count++;
                    }

                } else break;
            }
            if (count > max) max = count;
        }
        return max;
        }
    private static int twoLeft(String str) {
        int max1 = 0;
        for (int i = 0; i < str.length(); i++) {
            int count = 0;
            for (int j = i; j < str.length(); j++) {
                if (str.charAt(i) == str.charAt(j)) {
                    if(str.charAt(i)=='L'){
                        count++;
                    }

                } else break;
            }
            if (count > max1) max1 = count;
        }
        return max1;
        }

 int max = twoRight(str);
            int max1 = twoLeft(str);
            if(max >= 2 || max1 >=2) {
                System.out.println("YES");
            }else {

                System.out.println("NO");
            }

Input:

3
12
LRLRRRLRLLLL
2
LR
4
LRRL

Output:

YES
NO
YES

Link to original problem https://www.codechef.com/START16C/problems/DIRECTN/

Link To Run Code:- CLICK HERE

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More problems will be added regularly to this series.

CodeChef - ATM Problem

Atharva Siddhabhatti — Tue, 19 Oct 2021 15:46:34 +0000

CodeChef ATM Problem- Problem Code: HS08TEST

Basic Programming Series....

Problem Statement:- Pooja would like to withdraw X $US from an ATM. The cash machine will only accept the transaction if X is a multiple of 5, and Pooja's account balance has enough cash to perform the withdrawal transaction (including bank charges). For each successful withdrawal the bank charges 0.50 $US. Calculate Pooja's account balance after an attempted transaction.

Input

Positive integer 0 < X <= 2000 - the amount of cash which Pooja wishes to withdraw.

Nonnegative number 0<= Y <= 2000 with two digits of precision - Pooja's initial account balance.

Output

Output the account balance after the attempted transaction, given as a number with two digits of precision. If there is not enough money in the account to complete the transaction, output the current bank balance.

Explanation

Entered amount must be multiple of 5 that's why we are checking it by using modulus operator which returns the remainder of the numbers after dividing it with 0, if the remainder is 0 then it is multiple of 5. Second condition is to check whether the withdraw amount is available in her bank account after adding the 0.50$ charges, If both the condition are true then this expression is executed "balance = balance-amount-charges". If both condition doesn't satisfy then the available balance needs to be printed.

Also the output is required number with two digits of precision i.e balance must be shown with two decimal points. for that the below printf statement is used to format the output as per our need.

if(amount%5==0 && amount+charges<=balance) {
            balance = balance-amount-charges;

System.out.printf("%.2f", balance);

Example - Successful Transaction

Input:

30 120.00

Output:

89.50

Example - Incorrect Withdrawal Amount (not multiple of 5)

Input:

42 120.00

Output:

120.00

Example - Insufficient Funds

Input:

300 120.00

Output:

120.00

Check output here:- CLICK HERE

Link to the Series:- CLICK HERE

Link to original problem https://www.codechef.com/problems/HS08TEST

LIKE! SHARE! COMMENT!

More problems will be added regularly to this series.

Spring Boot - Pagination and Sorting Project

Atharva Siddhabhatti — Sun, 17 Oct 2021 16:04:18 +0000

Pagination is often helpful when we have a large dataset and we want to present it to the user in smaller chunks.
Also, we often need to sort that data by some criteria while paging.

Installation

1) Clone the Repo from here CLICK HERE

2) Import Maven based project in any of your Favourite IDE.

./mvnw spring-boot:run

Output

Open in Browser

Access H2 Database.

http://localhost:8080/h2-console

Output

Endpoint	Method	Body	Description
http://localhost:8080/student/search	GET	-	To get all students in paginated format
http://localhost:8080/student	POST	{ "id":214214,"name":"Atharva","rollno":32 }	To Add Students to the DB
http://localhost:8080/pagination?pageSize=5	GET	-	to get first 5 student details
http://localhost:8080/pagination?pageSize=5&pageNo=1	GET	-	To get student details by pagesize 5 and pageno 2
http://localhost:8080/pagination?pageSize=5&pageNo=2	GET	-	To get student details by pagesize 5 and pageno 1
http://localhost:8080/pagination?pageSize=5&pageNo=1&sortBy=id	GET	-	To sort student details by id
http://localhost:8080/pagination?pageSize=5&pageNo=1&sortBy=name	GET	-	To sort student by name

Usage

SortingRepository.java

@Repository
public interface SortingRepository extends PagingAndSortingRepository<Student, Integer>  {

}

StudentService.java

public PaginatedStudentResponse readStudent(Pageable pageable) {
        Page<Student> students = studentRepository.findAll(pageable);
        return PaginatedStudentResponse.builder()
                .numberOfItems(students.getTotalElements()).numberOfPages(students.getTotalPages())
                .studentList(students.getContent())
                .build();

    }

    public List<Student> getAllStudents(Integer pageNo, Integer pageSize, String sortBy)
        {
            Pageable paging = PageRequest.of(pageNo, pageSize, Sort.by(sortBy));
            Page<Student> pageResult = studentRepository.findAll(paging);

            if(pageResult.hasContent()) {
                return pageResult.getContent();
            }
            else
            {
                return new ArrayList<Student>();
            }
        }

    public Student createStudent(Student student) {
        return studentRepository.save(student);
    }

PaginationController.java


    @GetMapping
    public ResponseEntity<List<Student>> getAllStudents(
            @RequestParam(defaultValue = "0") Integer pageNo,
            @RequestParam(defaultValue = "10") Integer pageSize,
            @RequestParam(defaultValue = "id") String sortBy)
    {
        List<Student> list = service.getAllStudents(pageNo, pageSize, sortBy);

        return new ResponseEntity<List<Student>>(list, new HttpHeaders(),HttpStatus.OK);
    }

StudentController.java

@Autowired
    private StudentService studentService;

    @GetMapping("/student/search")
    public ResponseEntity<PaginatedStudentResponse> readStudent(Pageable pageable) {
        return ResponseEntity.ok(studentService.readStudent(pageable));
    }

    @PostMapping("/student")
    public ResponseEntity<Student> createProduct(@RequestBody Student student){
        return ResponseEntity.ok().body(this.studentService.createStudent(student));
    }

Configuration

application.properties

spring.jpa.show-sql = true

# Enabling H2 Console
spring.datasource.url=jdbc:h2:mem:testdb
spring.jpa.defer-datasource-initialization=true
spring.h2.console.enabled=true

# Enable Web Access
spring.h2.console.settings.web-allow-others=true

Credits

https://howtodoinjava.com

Spring Boot One To Many Mapping Demo With H2 database

Atharva Siddhabhatti — Fri, 15 Oct 2021 07:44:11 +0000

There are three basic entity relationships:-

One-to-One
One-to-Many/Many-to-one
Many-to-Many

A Single post can have multiple comments by this way we can apply one-to-many Mapping

Installation

Clone the repo from here:- Click here

Import Maven based project in any of your Favourite IDE.

./mvnw spring-boot:run

Output

Open in Browser

Access H2 Database.

http://localhost:8080/h2-console

Usage

MainClass.java

run() method is run when the application is started. The data is added in the database.

    Post post = new Post("Spring Boot Post Title","Spring Boot Post Description");
        Comment comment1 = new Comment("Thanks for uploading");
        Comment comment2 = new Comment("Comment2 test");
        Comment comment3 = new Comment("Comment3 test");

        post.getComments().add(comment1);
        post.getComments().add(comment2);
        post.getComments().add(comment3);

        postRepository.save(post);

Post.java

Id column is used to map the post and comments together.

@OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "post_Comment_id",referencedColumnName = "id")
    List<Comment> comments = new ArrayList<>();

Output

Comments are mapped by the ID of the Post on which they are commented. As you can see in the below images.

Configuration

application.properties

spring.jpa.show-sql = true

# Enabling H2 Console
spring.datasource.url=jdbc:h2:mem:testdb
spring.jpa.defer-datasource-initialization=true
spring.h2.console.enabled=true

# Enable Web Access
spring.h2.console.settings.web-allow-others=true

Tech Mahindra "Student Report" Recruitment Exam Question

Atharva Siddhabhatti — Thu, 14 Oct 2021 16:52:41 +0000

Statement :-

Given a list of N students, every student is marked for M subjects. Each student is denoted by an index value. Their teacher Ms. Margaret must ignore the marks of any 1 subject for every student. For this she decides to ignore the subject which has the lowest class average.
Your task is to help her find that subject, calculate the total marks of each student in all the other subjects and then finally return the array of the total marks scored by each student.

Input Specification:
input1:
An integer value N denoting number of students

input2:
An integer value M denoting number of subjects

input3:
A 2-D integer array of size N'M containing the marks of all students in each subject.

Output Specification:

Return an integer array of size N containing the total marks of each student afte deducting the score for that one subject.

Example 1:

INPUT

3 5
75 76 65 87 87
78 76 68 56 89
67 87 78 77 65

OUTPUT

325 299 296

Example 2:

INPUT

OUTPUT

120 129 129

Explanation:

Out of these subjects, the students average was lowest in subject 2
i.e 30+70+20= 120/3=40

So the teacher will ignore marks of this subject and will consider the title other two subjects for each of the three students i.e. 120 129 129 respectively

Hence (120 129 129) is returned as the final output.

Click Here to RUN CODE

Solution:-

import java.util.Scanner;

public class MyClass {
    public static void main(String args[]) {
      Scanner sc = new Scanner(System.in);
        int noOfStudents = sc.nextInt();
        int noOfSubjects = sc.nextInt();
        int index=0;
        int[] avg = new int[noOfSubjects];
        int[] total = new int[noOfSubjects];
        int[] result = new int[noOfStudents];
        int[][] marks = new int[noOfStudents][noOfSubjects];

        for(int i=0;i<noOfStudents;i++)
        {
            for(int j=0;j<noOfSubjects;j++) {
                marks[i][j] = sc.nextInt();
            }
        }
        for(int i=0;i<noOfSubjects;i++)
        {
            for(int j=0;j<noOfStudents;j++) {
                total[i] += marks[j][i];

            }
        }
        for(int j=0;j<noOfSubjects;j++) {
        //  System.out.print(total[j]+" ");
        }
        // System.out.println("");
        for(int j=0;j<noOfSubjects;j++) {
            avg[j] = total[j]/noOfSubjects;

        //  System.out.print(avg[j]+" ");
        }
        int min = avg[0];

          for(int i = 0; i < avg.length; i++)
           {
                if(min > avg[i])
                {
                    min = avg[i];
                    index=i;
                }
            }
        //  System.out.println(index);

          for(int i=0;i<noOfStudents;i++)
            {
                for(int j=0;j<noOfSubjects;j++) {
                    if(j!=index) {
                    result[i] += marks[i][j];

                    }
                }
            }
          for(int j=0;j<result.length;j++) {
                System.out.print(result[j]+" ");
            }

    }
}

Spring Boot One-To-One Mapping Demo With H2 database

Atharva Siddhabhatti — Wed, 13 Oct 2021 19:48:22 +0000

There are three basic entity relationships:-

One-to-One
One-to-Many/Many-to-one
Many-to-Many

Installation

Clone project from here:- Click Here
Import Maven based project in any of your Favourite IDE.

./mvnw spring-boot:run

Output

Open in Browser

Access H2 Database.

http://localhost:8080/h2-console

Usage

MainClass.java

run() method is run when the application is started. The data is added in the database.

    @Override
    public void run(String... args) throws Exception {
        Customer customer = new Customer();
        customer.setName("Atharva Siddhabhatti");
        customer.setEmail("atharvasiddhabhatti@gmail.com");
        Item item = new Item();
        item.setName("Macbook");
        item.setQty(1);
        customer.setItem(item);
        item.setCustomer(customer);
        customerRepository.save(customer);

Customer.java

Following annotations are used in the Customer Entity class to join two tables.Check the class file to view other entities.

@OneToOne(fetch =FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumn(name = "item_id")
    private Item item;

Item.java

@OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "item")
    private Customer customer;

Output

Configuration

application.properties

spring.jpa.show-sql = true

# Enabling H2 Console
spring.datasource.url=jdbc:h2:mem:testdb
spring.jpa.defer-datasource-initialization=true
spring.h2.console.enabled=true

# Enable Web Access
spring.h2.console.settings.web-allow-others=true

Spring Boot CRUD - Mongo DB + Docker

Atharva Siddhabhatti — Sun, 10 Oct 2021 20:23:46 +0000

CRUD Operations using Spring Boot and Mongo DB Database using docker-compose.

Docker is required to be install on the machine. Install Docker from here

Installation

1) Clone the Repo from here Click Here & run the following commands.

docker-compose up

Output

Endpoint	Method	Body	Description
http://localhost:8080/products	GET	-	Fetch all products
http://localhost:8080/products/{id}	GET	-	Find Product by Id
http://localhost:8080/products	POST	{ "id":"1", "name":"Mobile", "Description":"Samsung Mobile." }	To Add product to the DB
http://localhost:8080/products	PUT	{ "id":"1", "name":"Apple Iphone", "Description":"Apple" }	To update existing record.
http://localhost:8080/products/{id}	DELETE	-	Delete the record be Id

Usage

ProductRepository.java

@Repository
public interface ProductRepository extends MongoRepository<Product, Integer> {

}

Configuration

application.properties

spring.data.mongodb.host=mongo_db
spring.data.mongodb.port=27017
spring.data.mongodb.database=mydb

docker-compose.yml

version: '3.3'

services:
    #service 1: definition of mongo database
    mongo_db:
      image: mongo
      container_name: mongoDB  
      restart: always
      ports:
        - 27017:27017


    #service 2: definition of your spring-boot app 
    productservice:                        #it is just a name, which will be used only in this file.
      image: product-service               #name of the image after dockerfile executes
      container_name: product-service-app  #name of the container created from docker image
      build:
        context: .                          #docker file path (. means root directory)
        dockerfile: Dockerfile              #docker file name
      ports:
        - "8080:8080"                       #docker containter port with your os port
      restart: always  
      depends_on:                           #define dependencies of this app
        - mongo_db                                #dependency name (which is defined with this name 'db' in this file earlier)

Dockerfile

FROM openjdk:11 as mysqldoc
EXPOSE 8084
WORKDIR /app

# Copy maven executable to the image
COPY mvnw .
COPY .mvn .mvn

# Copy the pom.xml file
COPY pom.xml .

# Copy the project source
COPY ./src ./src
COPY ./pom.xml ./pom.xml

RUN chmod 755 /app/mvnw

RUN ./mvnw dependency:go-offline -B

RUN ./mvnw package -DskipTests
RUN ls -al
ENTRYPOINT ["java","-jar","target/springboot-demo-mysql-0.0.1-SNAPSHOT.jar"]