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Home > Programming > Reactive Programming > Learning Reactive Programming With Java 8
Learning Reactive Programming With Java 8
Learning Reactive Programming With Java 8

Learning Reactive Programming With Java 8: Learn how to use RxJava and its reactive Observables to build fast, concurrent, and powerful applications through detailed examples

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Profile Icon Nickolay Tzvetinov
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Learning Reactive Programming With Java 8

Chapter 2. Using the Functional Constructions of Java 8

Functional programming is not a new idea; actually, it's pretty old. For example, Lisp, which is a functional language, is the second oldest of today's commonly-used programming languages.

Functional programs are built using small pieces of reusable pure functions (lambdas). The program logic is composed of small declarative steps and not complex algorithms. That's because functional programs minimize the use of state, which makes imperative programs complex and hard to refactor/support.

With Java 8, the Java world got the lambda expressions and the ability to pass functions to functions. With them, we can code in a more functional style and get rid of a lot of the boilerplate code. The other new thing we got with Java 8 is the streams—something very similar to RxJava's observables but not asynchronous. Combining these streams and the lambdas, we are able to create more functional-like programs.

We...

Lambdas in Java 8

The most important change in Java 8 is the introduction of lambda expressions. They enable faster, clearer coding and make it possible to use functional programming.

Java was created back in the '90s as an object-oriented programming language, with the idea that everything should be an object. At that time, object-oriented programming was the principal paradigm for software development. But, recently, functional programming has become increasingly popular because it is well-suited for concurrent and event-driven programming. This doesn't mean that we should stop writing code using object-oriented languages. Instead, the best strategy is to mix elements of object-oriented and functional programming. Adding lambdas to Java 8 ties in with this idea—Java is an object-oriented language, but now it has lambdas, we are able to code using the functional style too.

Let's look at this new feature in detail.

Introducing the new syntax and semantics

In order to...

Implementing the reactive sum example with lambdas

So this time, our main piece of code will be quite similar to the previous one:

ConnectableObservable<String> input = CreateObservable.from(System.in);

Observable<Double> a = varStream("a", input);
Observable<Double> b = varStream("b", input);

reactiveSum(a, b); // The difference

input.connect();

The only difference is that we are going to take a more functional approach in calculating our sum and not to keep the same state. We won't be implementing the Observer interface; instead, we are going to pass lambdas to subscribe. This solution is much cleaner.

The CreateObservable.from(InputStream) method is a lot like we used previously. We will skip it and look at the Observable<Double> varStream(String, Observable<String>) method, which creates the Observable instances representing the collectors:

public static Observable<Double> varStream(
  final String name, Observable<String...

Pure functions and higher order functions

You don't have to remember most of the terms introduced in this chapter; the important thing is to understand how they help us write simplistic but powerful programs.

RxJava's approach has many functional ideas incorporated, so it is important for us to learn how to think in more functional ways in order to write better reactive applications.

Pure functions

A pure function is a function whose return value is only determined by its input, without observable side effects. If we call it with the same parameters n times, we are going to get the same result every single time. For example:

Predicate<Integer> even = (number) -> number % 2 == 0;
int i = 50;
while((i--) > 0) {
  System.out.println("Is five even? - " + even.test(5));
}

Each time, the even function returns False because it depends only on its input, which is the same each time and is not even.

This property of pure functions is called idempotence. Idempotent functions...

Summary

In this chapter, we've looked at some of the functional programming principles and terms. We've learned how to write programs composed of small pure function actions, chained together using higher order functions.

As functional programming is getting increasingly popular, developers proficient in it will be in high demand in the very near future. That's because it helps us achieve scalability and parallelism with ease. And what is more, if we add the reactive idea to it, it becomes even more appealing.

That's why we are going to dive into the RxJava framework in the next chapters, learning how to use it for our benefit. We'll begin with the Observable instance creation techniques. This will provide us with the skill to create an Observable instance from everything, thus turning almost everything into a functional reactive program.

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Description

If you are a Java developer that knows how to write software and would like to learn how to apply your existing skills to reactive programming, this book is for you.

Who is this book for?

If you are a Java developer that knows how to write software and would like to learn how to apply your existing skills to reactive programming, this book is for you.

What you will learn

  • Discover what reactive programming is and how you can benefit from it
  • Get to grips with the new functional features of Java 8 and some functional theory
  • Create RxJava Observable instances from virtually any data source
  • Transform, filter, and accumulate your data using various RxJava operators
  • Combine multiple data sources in one dataset, using custom logic
  • Write concurrent programs with ease, scheduling actions on various workers
  • Learn about unit testing asynchronous RxJava logic
  • Extend RxJava by writing your own operators and factory methods

Product Details

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Publication date, Length, Edition, Language, ISBN-13
Publication date : Jun 24, 2015
Length: 182 pages
Edition : 1st
Language : English
ISBN-13 : 9781785282508
Vendor :
Oracle
Category :
Programming
Languages :
Java
Concepts :
Reactive Programming

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Publication date : Jun 24, 2015
Length: 182 pages
Edition : 1st
Language : English
ISBN-13 : 9781785282508
Vendor :
Oracle
Category :
Programming
Languages :
Java
Concepts :
Reactive Programming

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Learning Java Functional Programming
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Learning Reactive Programming With Java 8
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Table of Contents

9 Chapters
1. An Introduction to Reactive Programming Chevron down icon Chevron up icon
1. An Introduction to Reactive Programming
What is reactive programming?
Why should we be reactive?
Introducing RxJava
Summary
2. Using the Functional Constructions of Java 8 Chevron down icon Chevron up icon
2. Using the Functional Constructions of Java 8
Lambdas in Java 8
Implementing the reactive sum example with lambdas
Pure functions and higher order functions
Summary
3. Creating and Connecting Observables, Observers, and Subjects Chevron down icon Chevron up icon
3. Creating and Connecting Observables, Observers, and Subjects
The Observable.from method
The Observable.just method
Other Observable factory methods
The Observable.create method
Subscribing and unsubscribing
Hot and cold Observable instances
The Subject instances
Summary
4. Transforming, Filtering, and Accumulating Your Data Chevron down icon Chevron up icon
4. Transforming, Filtering, and Accumulating Your Data
Observable transformations
Filtering data
Accumulating data
Summary
5. Combinators, Conditionals, and Error Handling Chevron down icon Chevron up icon
5. Combinators, Conditionals, and Error Handling
Combining the Observable instances
The conditional operators
Handling errors
An HTTP client example
Summary
6. Using Concurrency and Parallelism with Schedulers Chevron down icon Chevron up icon
6. Using Concurrency and Parallelism with Schedulers
RxJava's schedulers
Buffering, throttling, and debouncing
Summary
7. Testing Your RxJava Application Chevron down icon Chevron up icon
7. Testing Your RxJava Application
Testing using simple subscription
The BlockingObservable class
The aggregate operators and the BlockingObservable class
Testing with the aggregate operators and the BlockingObservable class
Using the TestSubscriber class for in-depth testing
Testing asynchronous Observable instances with the help of the TestScheduler class
Summary
8. Resource Management and Extending RxJava Chevron down icon Chevron up icon
8. Resource Management and Extending RxJava
Resource management
Caching data with Observable.cache
Creating custom operators with lift
Composing multiple operators with the Observable.compose operator
Summary
Index Chevron down icon Chevron up icon
Index

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Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Half star icon Empty star icon 3.6
(5 Ratings)
5 star 40%
4 star 20%
3 star 20%
2 star 0%
1 star 20%
T. Nield Jul 31, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Pretty thorough book on RxJava, and even includes content on custom Operators and Transformers. the chapter on Schedulers was very well-explained and makes it clear how subscribeOn() and observeOn() behave. Although I had to re-read several parts of it, this book has helped me understand RxJava better than any other resource I have come across.I highly recommend downloading the source code to follow along rather than reading the code on paper.
Amazon Verified review Amazon
Amazon Customer Mar 29, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Good
Amazon Verified review Amazon
Dimitri K Feb 18, 2016
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
It is a nice book, thoughtfully written and with many details. One problem is that some complicated issues are explained too shortly, with few words and unclear diagrams, from which it is hard to understand the point. As if the author was in a hurry. I hope second edition will be improved.
Amazon Verified review Amazon
Marty Jul 28, 2017
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
READ THIS BEFORE BUYINGThis book is very well written, but it is very much out of date. RxJava 2 is very different from RxJava1 which is what this book is based on. If you import the latest version of RxJava, the very first code sample in this book doesn't even compile. I'm bummed because I spent over $20 on this ebook and I can't even use it. You're better off looking at online docs or wait for this author to write a new book.
Amazon Verified review Amazon
Bram Aug 02, 2016
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One can only assume that this book was reviewed by hamsters who were taught English as a second language. No native speaker so much as breathed in the direction of this book while it was being edited, and it shows.
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About the author

Profile icon Nickolay Tzvetinov
Nickolay Tzvetinov
Nickolay Tsvetinov is a professional all-round web developer at TransportAPI - Britain's first comprehensive open platform for transport solutions. During his career as a software developer, he experienced both good and bad and played with most of the popular programming languages - from C and Java to Ruby and JavaScript. For the last 3-4 years, he's been creating and maintaining single-page applications (SPA) and the backend API architectures that serve them. He is a fan of open source software, Rails, Vim, Sinatra, Ember.js, Node.js, and Nintendo. He was an unsuccessful musician and poet, but he is a successful husband and father. His area of interest and expertise includes the declarative/functional and reactive programming that resulted in the creation of ProAct.js (https://proactjs.github.io/), which is a library that augments the JavaScript language and turns it into a reactive language.
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