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

What the heck is Meteor DDP?

I was using Meteor for my messenger project. I was so curious about the real time connection. I wanted to know how exactly this mechanism works. In this post, I will go through the DDP Specification, an overview of WebSocket, and a simple demo about how to subscribe a publication of Rocket.Chat (containing a DDP server) from an external webpage. At a glance, I knew that Meteor invented a protocol called DDP which uses for handling real time connection. So then, what is DDP? "DDP (Distributed Data Protocol) is the stateful WebSocket protocol that Meteor uses to communicate between the client and the server." [1] All right! Why does DDP matter? "DDP is a standard way to solve the biggest problem facing client-side JavaScript developers: querying a server-side database, sending the results down to the client, and then pushing changes to the client whenever anything changes in the database" . [2] In order to understand deeply the protocol, I decided ...

Strategy Design Pattern

For example, I have a program with an Animal abstract class and two sub-classes Dog and Bird. I want to add new behavior for the class Animal, this is "fly". Now, I face two approaches to solve this issue: 1. Adding an abstract method "fly" into the class Animal. Then, I force the sub-classes should be implemented this method, something like: public abstract class Animal{ //bla bla public abstract void fly(); } public class Bird extends Animal{ //bla bla public void fly(){ System.out.println("Fly high"); } } public class Dog extends Animal{ //bla bla public void fly(){ System.out.println("Cant fly"); } } 2. Creating an interface with method "fly" inside. The same issue to an abstract class, I force the classes these implement this interface should have a method "fly" inside: public interface Flyable{ public void fly(); } public class Bird implements Flyable{ //bla bla public void fly(){ System.out.pr...

Journal: This Month I Learned (2022-Nov)

This Month I Learned posts are aimed to share what I have learned during the month such as my thoughts, recommend resources, tips, how-to, and so on. Vung Tau beach Engineering Levels I conducted a lot of meetings with HRM to define the standards for evaluation criteria, career path ladder, Personal Appraisal (PA) processes, and onboarding/offboarding processes. I knew more about the expectation from an HRM perspective for engineering levels evaluation criteria. For example Define many enough titles for a long career path development Define general criteria for each level How to calculate score when evaluation with weight matrix applied Anticipate risks before executing a process Team Engineering Lead Organization I collected ideas from different people When having no dedicated leader, every member of the team has a fairly chance to practice leadership skills Scalability strategy: development teams’ size, and new position nomination. Security Awareness Training I conducted this sharing...

DevOps Toolchain Enhancement

Historically, our company ubitec had started with a customer project. Agile/Scrum was our proposal for working with customers. Time by time, Agile/Scrum also became our culture for software development. To be successful with this development approach, we somehow needed to have a fast release for customers (i.e. every one week). Back then, we had a build tool Jenkins which was responsible for having sprint release packages for our customers. The build job pipelines contain some steps such as gathering the artifacts, checking the code convention, running the tests, building docker images, and packaging an archived file (a zip file). The set of tools involved in a pipeline is roughly called a toolchain. It is just a part of a bigger process called the DevOps toolchain. Source: https://www.ibm.com/blogs/cloud-archive/2016/11/devops-architecture-available-on-bluemix-garage-method-site/ DevOps is a proven method that fits Agile. Today, it is even treated as a mandatory factor...

Validate date with Datejs

Datejs is an open source JavaScript Date library for parsing, formatting and processing. Website: http://www.datejs.com function isValid(date, pattern){ if(pattern == null){ return false; } var parseExact = Date.pareExact(date, pattern); if(parseExact !== null){ return true; } return false; } Another popular date library is Moment.js

vhandit

Search This Blog