DEV Community: Ramesh Fadatare

Java Stream flatMap() Example

Ramesh Fadatare — Thu, 09 Dec 2021 11:21:40 +0000

The Java Stream flatMap() method is an intermediate operation.

The Stream.flatMap() function, as the name suggests, is the combination of a map and a flat operation. This means you first apply the map function and then flatten the result.

Java Stream flatMap() Example

To understand what flattening a stream consists in, consider a structure like [ [1,2,3],[4,5,6],[7,8,9] ] which has "two levels". It's basically a big List containing three more List. Flattening this means transforming it in a "one level" structure e.g. [ 1,2,3,4,5,6,7,8,9 ] i.e. just one list.

For example: In the below program, you can see that we have three lists that are merged into one by using a flatMap() function:

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args)
    {
        List<Integer> evens = Arrays.asList(2, 4, 6);
        List<Integer> odds = Arrays.asList(3, 5, 7);
        List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11);
        List<Integer> numbers = Stream.of(evens, odds, primes)
                .flatMap(list -> list.stream())
                .collect(Collectors.toList());
        System.out.println("flattend list: " + numbers);
    }
}

Output:

flattend list: [2, 4, 6, 3, 5, 7, 2, 3, 5, 7, 11]

Related Java Stream API's Examples

Java Stream map() Example

Ramesh Fadatare — Thu, 09 Dec 2021 11:17:54 +0000

The Java Stream map() method is an intermediate operation.

Java Stream map() Example

The Java Stream map() method converts (maps) an element to another object. For instance, if you had a list of strings it could convert each string to lowercase, uppercase, or to a substring of the original string, or something completely else.

Here is a Java Stream map() example: If you have a List of String and you want to convert that to a List of Integer, you can use map() to do so.

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Main 
{
    public static void main(String[] args) 
    {
        List<String> listOfStrings = Arrays.asList("1", "2", "3", "4", "5");

        List<Integer> listOfIntegers = listOfStrings.stream()
                        .map(Integer::valueOf)
                        .collect(Collectors.toList());

        System.out.println(listOfIntegers);
    }
}

Output:


[1, 2, 3, 4, 5]

Related Java Stream API's Examples

Java Stream filter() Example

Ramesh Fadatare — Thu, 09 Dec 2021 11:12:15 +0000

The Java Stream filter() is an intermediate operation.

The Java Stream filter() can be used to filter out elements from a Java Stream.

The filter() method takes a Predicate that is called for each element in the stream. If the element is to be included in the resulting Stream, the Predicate should return true. If the element should not be included, the Predicate should return false.

Java Stream filter() Example 1

Here is an example of calling the Java Stream filter() method:

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Tester {
   public static void main(String[] args){
        List<String> lines = Arrays.asList("java", "c", "python");

        List<String> result = lines.stream()       // convert list to stream
                .filter(line -> !"c".equals(line)) // we dont like c
                .collect(Collectors.toList());     // collect the output and convert streams to a List

        result.forEach(System.out::println);  
    }
}

Output:

java
python

Java Stream filter() Example 2

In this example, we will create a list of products and we filter products whose price is greater than 25k. We display a list of products using the forEach() method.

Let's first create a Product class:

class Product {
    private int id;
    private String name;
    private float price;
   // getters and setters 
}
public class StreamFilterExample {
    public static void main(String[] args) {

        // using stream API
        List < Product > filteredProducts = getProducts().stream()
            .filter((product) -> product.getPrice() > 25000 f)
            .collect(Collectors.toList());
        filteredProducts.forEach(System.out::println);
    }

    private static List < Product > getProducts() {
        List < Product > productsList = new ArrayList < Product > ();
        productsList.add(new Product(1, "HP Laptop", 25000 f));
        productsList.add(new Product(2, "Dell Laptop", 30000 f));
        productsList.add(new Product(3, "Lenevo Laptop", 28000 f));
        productsList.add(new Product(4, "Sony Laptop", 28000 f));
        productsList.add(new Product(5, "Apple Laptop", 90000 f));
        return productsList;
    }
}
In the above example, we are using the filter() method to filter products whose price is greater than 25k:
       List < Product > filteredProducts = getProducts().stream()
            .filter((product) -> product.getPrice() > 25000 f)
            .collect(Collectors.toList());

Related Java Stream Methods/APIs Examples

Best YouTube Channels to learn Spring Boot

Ramesh Fadatare — Tue, 23 Nov 2021 12:35:06 +0000

In this post, I will like to suggest a few best YouTube channels to learn Spring Boot.

1. @ Java Guides // my youtube channel

JavaGuides has 50K subscribers and is considered one of the best YouTube channels to learn Java, Spring Boot, and Full-stack development.

JavaGuides channel publishes video tutorials on the following technologies stack:

Core Java, Java EE(JSP, Servlet).
Spring Boot, Spring MVC, Spring AOP, Spring Rest, Spring Security, Spring data module, Spring Social, Spring Integration.
Angular Framework
ReactJS, React Hooks
Hibernate, JPA, Mybatis
Javascript, HTML and CSS
MySQL, MS-SQL, Postgres, Oracle, H2 database, MongoDB.
Git, Github, CVS, SVN, Ant.
NodeJS
Restful
AWS
Jersey Rest using JAX-RS, SOAP, Web Services.
Elastic Search
Hadoop (Hive, Pig, HDFS, Hbase)

2. @ Java Techie

3. @ Java Brains

4. @ Telusko

5. @ Tech Primers

6. @ Amigoscode

7. @ SpringDeveloper

8. @ in28minutes

9. @ Spring Framework Guru

If you know any other good YouTube channel to learn Spring boot then you can suggest in the comment section below.

Original Post

Best YouTube Channels to learn Spring Boot

Java Developer Road Map 2022

Ramesh Fadatare — Tue, 23 Nov 2021 12:09:43 +0000

In this article, we will discuss the Java developer road map or learning path for Java developer in 2022.

If you are a Java beginner and want to become a Java developer then you are in right place.

Video

This article is pretty well explained in the below video tutorial:
Java Developer Road Map - Learning Path for Java Developer

In this article, we will discuss:

Skills for Core Java development
Skills for Java EE development
Tools for Java development
Commonly used libraries for Java development

1. Skills for Core Java Development

As a Java beginner, start learning core Java development.

Here are the skills required you to work on Core Java development:

Core Java

Core Java is a base for all the Java EE frameworks and technologies so make sure that you have a good foundation in core java.

You can learn and master core Java at Java Tutorial | Learn Java Programming with Examples

Data Structures and Algorithms

Data Structures and Algorithms are the building blocks of any programming language.

As a programmer, you should have a good understanding of data structures and algorithms.

To learn and master Data Structures and Algorithms in Java at Data Structures and Algorithms in Java

Java Testing

Check out the JUnit framework and Mokito for unit testing in Java. As a Java programmer, you should have good knowledge of testing your core logic using the JUnit framework.

To learn and master the JUnit framework at JUnit tutorials

Knowledge on Databases

As a core Java developer, you should have good knowledge of databases.

Here are the commonly used relational databases and No SQL databases:

RDBMS:

MySQL
PostgreSQL
MS-SQL server
Oracle

No SQL Databases:

MongoDB
CouchDB
Elastic Search

Design Patterns(GOF)

In software engineering, a design pattern is a general repeatable solution to a commonly occurring problem in software design. A design pattern isn't a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations.

As a core Java programmer, you should know the commonly used design patterns in Java.
The GoF Design Patterns are broken into three categories:

Creational Patterns for the creation of objects;
Structural Patterns to provide relationships between objects
Behavioral Patterns to help define how objects interact.

Learn and master all the GOF design patterns at All GOF design patterns

Desktop Application Development

In the Java community, you have Swing and JavaFX to develop desktop-based applications.

Swing is a legacy library for building the desktop app and JavaFX is modern so we suggest you use JavaFX for desktop applications.

2. Skills for Java EE development

Once you are familiar with Core Java development then learn the below skills to work on Java EE development:

JSP and Servlets

JSP and Servlets are used to develop web applications.

Learn JSP at JSP Tutorial

Learn Servlet at Servlet Tutorial

JPA

The Java Persistence API (JPA) is the Java standard for mapping Java objects to a relational database. Mapping Java objects to database tables and vice versa is called Object-relational mapping (ORM).

JPA implementation is provided as a reference implementation by the vendors developing O/R Mapper such as Hibernate, EclipseLink, and Apache OpenJPA.
Learn JPA at JPA Tutorial

JAX-RS

JAX-RS is Java API for RESTful Web Services (JAX-RS) is a Java programming language API spec that provides support in creating web services according to the Representational State Transfer (REST) architectural pattern.
There are two main implementations of the JAX-RS API:

Jersey Framework
RESTEasy

Learn Jersey Framework at Jersey Framework Tutorials
Learn RESTEasy at RESTEasy Tutorials

JAX-WS

Java API for XML Web Services (JAX-WS) is a standardized API for creating and consuming SOAP (Simple Object Access Protocol) web services.

Hibernate Framework

As a Java EE programmer, you must learn the Hibernate framework to develop the DAO layer.

Hibernate is a java based ORM tool that provides a framework for mapping application domain objects to the relational database tables and vice versa.

Hibernate is probably the most popular JPA implementation and one of the most popular Java frameworks in general. Hibernate acts as an additional layer on top of JDBC and enables you to implement a database-independent persistence layer. It provides an object-relational mapping implementation that maps your database records to Java objects and generates the required SQL statements to replicate all operations to the database.

Learn Hibernate at Hibernate ORM Tutorials

Spring Framework

Spring framework makes Java EE development easier. Spring framework is a must-learn skill for Java EE developers.

The Spring Framework is a Java platform that provides comprehensive infrastructure support for developing Java applications. Spring handles the infrastructure so application developers can focus on your application.

Learn Spring at Spring Tutorials

Spring Boot

Spring Boot is basically an extension of the Spring framework which eliminated the boilerplate configurations required for setting up a Spring application.

Spring Boot is an opinionated framework that helps developers build Spring-based applications quickly and easily. The main goal of Spring Boot is to quickly create Spring-based applications without requiring developers to write the same boilerplate configuration again and again.

Spring boot is one of the essential skill for Java EE developers right now.
Learn Spring boot at Learn and master Spring Boot

Microservices

Spring Boot and Spring Cloud is a great combination to develop a microservices in Java.

Spring Boot is the most popular and widely used Java framework for building MicroServices. These days many organizations prefer to deploy their applications in a Cloud environment instead of taking all the headache of maintaining a datacenter themselves. But we need to take good care of the various aspects to make our applications Cloud Native. There comes the beauty of Spring Cloud.

Spring Cloud is essentially an implementation of various design patterns to be followed while building Cloud Native applications. Instead of reinventing the wheel, we can simply take advantage of various Spring Cloud modules and focus on our main business problem than worrying about infrastructural concerns.

3. Tools for Java development

Apart from Core Java and Java EE skills, it's important to learn about tools required for Java project development. As a Java developer, you should learn the below tools to work on Java development:

Maven
Gradle
Git
Jenkins
SVN
JIRA
Docker
AWS
Kubernetes
Eclipse or Intellij idea

4. Commonly used libraries for Java development

It's also important for Java developers to learn commonly used utility libraries for Java development.
Here are the commonly used Java utility libraries:

Conclusion

In this article, we have discussed the technologies, tools, and libraries required to become a Java developer.
We have discussed the below topics in this article:

Skills for Core Java development
Skills for Java EE development
Tools for Java development
Commonly used libraries for Java development

Original Post

Java Developer Road Map 2021 - Learning Path for Java Developer

YouTube Video Link

Java Developer Road Map - Learning Path for Java Developer

Java HashMap Examples

Ramesh Fadatare — Wed, 17 Nov 2021 07:27:04 +0000

This page contains source code examples of the HashMap class in Java. On this page, we will learn everything about the Java HashMap class with source code examples.

Java HashMap Examples

HashMap Stream and Filtering Example

Java HashMap Iteration over Values Example

Java HashMap Iteration over Keys

Java HashMap replace() Example

Java HashMap size Example

Iterate over a HashMap Java using Lambda

Iterate over a HashMap Java 8 forEach

Iterating over a HashMap using Iterator in Java

Iterate over HashMap in Java

How to Store Employee Objects in HashMap

Remove Entry from HashMap Java

Check If Value Exists in HashMap Java Example

Check If Key Exists in HashMap Java Example

Create a HashMap in Java Example

Original Post

Java Collections Framework Examples

Java LinkedList Examples

Ramesh Fadatare — Wed, 17 Nov 2021 07:21:03 +0000

This page contains source code examples of the LinkedList class in Java. On this page, you will learn everything about the Java LinkedList class with source code examples.

Following are some key points to note about LinkedList in Java -

Java LinkedList maintains the insertion order of the elements.
LinkedList can have duplicate and null values.
The LinkedList class implements Queue and Deque interfaces. Therefore, It can also be used as a Queue, Deque, or Stack.
Java LinkedList is not thread-safe. You must explicitly synchronize concurrent modifications to the LinkedList in a multi-threaded environment.

Java LinkedList Examples

Original Post

Java LinkedList Examples

Java ArrayList Examples

Ramesh Fadatare — Wed, 17 Nov 2021 07:16:18 +0000

This page contains 40+ source code examples of the ArrayList class in Java.

On this page, we will learn everything about the Java ArrayList class with source code examples. We will learn about different ArrayList operations and methods with the help of coding examples.

Following are few key points to note about ArrayList in Java -

An ArrayList is a re-sizable array, also called a dynamic array. It grows its size to accommodate new elements and shrinks the size when the elements are removed.
ArrayList internally uses an array to store the elements. Just like arrays, It allows you to retrieve the elements by their index.
Java ArrayList allows duplicate and null values.
Java ArrayList is an ordered collection. It maintains the insertion order of the elements.
You cannot create an ArrayList of primitive types like int, char etc. You need to use boxed types like Integer, Character, Boolean etc.
Java ArrayList is not synchronized. If multiple threads try to modify an ArrayList at the same time, then the final outcome will be non-deterministic. You must explicitly synchronize access to an ArrayList if multiple threads are gonna modify it.

Java ArrayList Examples

Original Post

Java ArrayList Examples

Full Stack Java Developer Road Map 2022

Ramesh Fadatare — Wed, 17 Nov 2021 06:57:18 +0000

In this article, I am going to talk about how to become a full-stack java developer.

Well if you are a Java developer and if you want to become a full-stack Java developer then you are in a right place and if you are a Java beginner and if you want to become a full-stack Java developer then you are also in the right place.

In this article, I am going to give you a learning path to become a full-stack java developer so basically, we will discuss what are the skills I mean what are the tools and technologies that you are going to learn to become a full-stack java developer.

Before looking to the learning path for full-stack java developer let's first understand what is a full stack developer. Well full stack developer is an engineer who works on both client-side and server-side software. Full-stack developers have the capability to develop applications from start to end because a full stack developer has hands-on experience on both server-side technologies as well as client-side technologies.

Video

Complete article explained in the below YouTube video:

As a full-stack Java developer, you should know the front-end technologies, back-end technologies, databases, and tools to develop any software from end to end right.

1. Front-end Technologies

let's take a look into what are the skills that are required to work on front-end development.

HTML, CSS and JavaScript

HTML, CSS, and JavaScript are web development fundamentals so make sure that you should have good knowledge of these web technologies.

HTML is used to develop web pages.
CSS is used to style HTML web pages.
JavaScript is used to manipulate HTML DOM.

Angular, ReactJS and VueJS

As a full-stack Java developer, you should at least one of these modern front-end frameworks such as Angular or React or VueJS.

Angular is a platform and framework for building client applications in HTML and TypeScript. Angular is written in TypeScript. It implements core and optional functionality as a set of TypeScript libraries that you import into your apps.

Learn Angular at https://www.javaguides.net/p/angular-8-tutorial-with-examples.html

React is an open-source javascript library for building user interfaces. React is a project created and maintained by Facebook. React has a component-based architecture. This lets you break down your application into small encapsulated parts which can then be composed to make a more complex UI.

Learn React at https://www.javaguides.net/p/reactjs-tutorial.html

Vue is a progressive framework for building user interfaces. Unlike other monolithic frameworks, Vue is designed from the ground up to be incrementally adoptable. The core library is focused on the view layer only and is easy to pick up and integrate with other libraries or existing projects. On the other hand, Vue is also perfectly capable of powering sophisticated Single-Page Applications when used in combination with modern tooling and supporting libraries.

NodeJs and NPM

Node.js is an open-source, cross-platform, back-end, JavaScript runtime environment that executes JavaScript code outside a web browser.

You need NPM which is a package manager to install JavaScript packages or libraries.

2. Back-end Technologies

Core Java

Core Java is a base for all the Java EE frameworks and technologies so make sure that you have a good foundation in core java.

Spring Framework

Spring framework makes Java EE development easier. Spring framework is a must-learn skill for Java EE developers.

Learn Spring Framework at Learn Spring Framework

Spring Boot

Spring Boot is basically an extension of the Spring framework which eliminated the boilerplate configurations required for setting up a Spring application.

Spring Boot is an opinionated framework that helps developers build Spring-based applications quickly and easily. The main goal of Spring Boot is to quickly create Spring-based applications without requiring developers to write the same boilerplate configuration again and again.

Learn Spring Boot at Spring Boot Tutorial

Hibernate Framework

As a Java EE programmer, you must learn the Hibernate framework to develop the DAO layer.

Hibernate is a java based ORM tool that provides a framework for mapping application domain objects to the relational database tables and vice versa.

Learn Hibernate at Learn Hibernate ORM Framework

Spring Security

Spring security is one of the popular framework out there for implementing Authentication and Authorization features. To secure REST API's and web applications, I suggest you use Spring security in the Java community.

Learn Spring security at Learn Spring Security

Microservices

Spring Boot and Spring Cloud is a great combination to develop a microservices in Java.

3. Knowledge of Databases

As a full-stack Java developer, you should have good knowledge of databases.

Here are the commonly used relational databases and No SQL databases:

RDBMS:

MySQL
PostgreSQL
MS-SQL server
Oracle No SQL Databases:
MongoDB
CouchDB
Elastic Search

4. Tools

As a full-stack Java developer, you should know the below tools to develop and deploy web apps.
Here is the list of essential tools for full-stack Java developers:

Apache Maven
Gradle
Git
Jenkins
Eclipse and IntelliJ IDEA
Docker
JIRA
SVN
Apache Ant
Java Decompiler

Original Post

How to Become a Full Stack Java Developer - Learning Path for Full Stack Java Developer