Functional programming in Java 8

In my previous post, we discussed about why we should consider to use functional programming. Now, let's delve into what functional programming in Java is.

What is pure functional programming?

Shortly, functional programming is programming using functions. A function corresponds to a mathematical function such as log, sin. Basically, it takes zero or more arguments, give one or more result, and has no side effects.

We can't completely program in pure functional style in Java

Why? For example, calling Scanner.nextLine twice typically gives different result.

So, it's just called "functional-style programming". How is that?
- There is no mutating structures visible to callers. That means your side effect may not be visible to a program, but it's visible to the programmer in terms of slower execution.
- A function or method shouldn't throw any exceptions (follows the concept "pass arguments, return result"). We can use types like Optional<T> instead.
- For pragmatic reasons, we can accept some code that can't be strictly described as functional, e.g: some form of log file.

We call it "no visible side effects" or referential transparency

With functional-style programming, we follow the rule "no visible side-effects" includes no mutating structures visible to callers, no I/O and no exceptions. This concept is called "referential transparency". A function is referentially transparent if it always returns the same result value when called with the same argument value. For example, "huong".replace("h", "H") but Random.nextInt

Will function-style programming replace object-oriented programming?

Why? And, why not? These are just programming styles. It depends!
In practice, Java programmers have always mixed object-oriented and functional-style programming styles.
- Object-oriented programming style: everything is an object and programs operate by updating fields and calling methods that update their associated object.
- Functional-style programming style: referential transparency. It helps enable you to write programs that are more modular and more suitable for multicore processors. These ideas are as additional weapons in your programming armory.

Reference

Image result for java 8 in action

[1]. Alan Mycroft and Mario Fusco, Java 8 in Action: Lambdas, Streams, and Functional-style Programming. Part 4. Beyond Java 8.

Comments

Junit - Test fails on French or German string assertion

In my previous post about building a regex to check a text without special characters but allow German and French . I met a problem that the unit test works fine on my machine using Eclipse, but it was fail when running on Jenkins' build job. Here is my test: @Test public void shouldAllowFrenchAndGermanCharacters(){ String source = "ÄäÖöÜüß áÁàÀâÂéÉèÈêÊîÎçÇ"; assertFalse(SpecialCharactersUtils.isExistSpecialCharater(source)); } Production code: public static boolean isExistNotAllowedCharacters(String source){ Pattern regex = Pattern.compile("^[a-zA-Z_0-9_ÄäÖöÜüß áÁàÀâÂéÉèÈêÊîÎçÇ]*$"); Matcher matcher = regex.matcher(source); return !matcher.matches(); } The result likes the following: Failed tests: SpecialCharactersUtilsTest.shouldAllowFrenchAndGermanCharacters:32 null A guy from stackoverflow.com says: "This is probably due to the default encoding used for your Java source files. The ö in the string literal in the J...

How to apply Lean - Kanban for your business

This is the topic of Scrum Breakfast meetup this time, speaker: Ms. Phuong Bui - Technical Project Manager of YOOSE Pte. Ltd. http://www.meetup.com/Scrum-Breakfast-Vietnam-Agile-and-Scrum-Meetup/events/230313727/ Lean comes from Lean manufacturing is a method that focuses on elimination of wastes. In other words, this is a set of principles for archiving the quality, speed and customer alignment. The first time I knew about the term "Lean" is from the book Software Craftsmanship . Sandro recommends if we want to transform our pet projects into a real business, we should get familiar with Lean Startup concepts. In this talk, Ms. Phuong pointed out some major wastes includes information (ex: unclear requirements), processes (ex: waiting), physical environment and people. Knowing what the problems should be the best way to eliminate them. The difference between Single item flow and Batch processing is the second main point; and it is the Lean's idea. Batch pr...

My must-have apps for daily work

There is no doubt that cool apps can help us be more productive and enjoyable at work. For the time being, I really love the following apps which are used by me almost every day. 1. A personal Kanban In fact, a personal kanban is the most useful app for me. Why does it matter? It is not just a to-do list, but it keeps me motivated every day because it helps me be able to know what my "big picture" is. I usually set up my plans together with a path to reach them. KanbanFlow is my preferred tool. KanbanFlow 2. A terminal Needless to say, a terminal is a must-have app for every developer, especially the ones use macOS/Linux. Due to its importance, I love to decorate and enhance it to be super exciting with various tools such as iTerm , oh-my- zsh , and thefuck . ;) iTerm + oh-my-zsh 3. A documentation "ecosystem" As a developer, I can not remember all things that I have experimented a day. Moreover, a document is really useful for sharing an...

Performance of a Data Structure

Why data structures matter The fact is that programs are all about processing data. Data structures are referred to how data is organized which affects the time of executing a program. How to measure the performance of a data structure In order to measure "how fast"/efficiency/performance of a data structure, we measure the performance of its operations. There are four basic operations including reading , searching , insertion , and deletion . A pure time consuming is not used for the measuring because it is not reliable depending on the hardware that it is run on. But instead, we use the term time complexity which refers to how many steps an operation takes. An example of how a single rule can affect efficiency Let's compare two data structures: Array and Set (with N elements). 1. Array - Reading : 1 step (because the computer has the ability to jump to any particular index in the array) - Searching : N steps (the worst case with linear search) - Inserti...

How I did customize "rasa-nlu-trainer" as my own tool

Check out my implementation here Background I wanted to have a tool for human beings to classify intents and extract entities of texts which were obtained from a raw dataset such as Rocket.chat's conversation, Maluuba Frames or here . Then, the output (labeled texts) could be consumed by an NLU tool such as Rasa NLU. rasa-nlu-trainer was a potential one which I didn't need to build an app from scratch. However, I needed to add more of my own features to fulfill my needs. They were: 1. Loading/displaying raw texts stored by a database such as MongoDB 2. Manually labeling intents and entities for the loaded texts 3. Persisting labeled texts into the database I firstly did look up what rasa-nlu-trainer 's technologies were used in order to see how to implement my mentioned features. At first glance rasa-nlu-trainer was bootstrapped with Create React App. Create React App is a tool to create a React app with no build configuration, as it said. This too...

vhandit

Search This Blog