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

Why Functional Programming Matter

What issues do we concern when implementing and maintaining systems? One of the most concern is debugging during maintenance: "this code crashed because it observed some unexpected value." Then, it turns out that the ideas of no side effects and immutability , which functional programming promotes, can help. Shared mutable data is the root cause Shared mutable data are read and updated by more than one of the methods. Share mutable data structures make it harder to track changes in different parts of your program. An immutable object is an object that can't change its state after it's instantiated so it can't be affected by the actions of a function. It would be a dream to maintain because we wouldn't have any bad surprises about some object somewhere that unexpectedly modifies a data structure. A new thinking: Declarative programming There are two ways thinking about implementing a system by writing a program. - Imperative programming: has...

The HelloWorld example of JSF 2.2 with Myfaces

I just did by myself create a very simple app "HelloWorld" of JSF 2.2 with a concrete implementation Myfaces that we can use it later on for our further JSF trying out. I attached the source code link at the end part. Just follow these steps below: 1. Create a Maven project in Eclipse (Kepler) with a simple Java web application archetype "maven-archetype-webapp". Maven should be the best choice for managing the dependencies , so far. JSF is a web framework that is the reason why I chose the mentioned archetype for my example. 2. Import dependencies for JSF implementation - Myfaces (v2.2.10) into file pom.xml . The following code that is easy to find from http://mvnrepository.com/ with key words "myfaces". <dependency> <groupId>org.apache.myfaces.core</groupId> <artifactId>myfaces-api</artifactId> <version>2.2.10</version> </dependency> <dependency> <groupId>org.apache.myfaces.core<...

Coding Exercise, Episode 1

I have received the following exercise from an interviewer, he didn't give the name of the problem. Honestly, I have no idea how to solve this problem even I have tried to read it three times before. Since I used to be a person who always tells myself "I am not the one good at algorithms", but giving up something too soon which I feel that I didn't spend enough effort to overcome is not my way. Then, I have sticked on it for 24 hours. According to the given image on the problem, I tried to get more clues by searching. Thanks to Google, I found a similar problem on Hackerrank (attached link below). My target here was trying my best to just understand the problem and was trying to solve it accordingly by the Editorial on Hackerrank. Due to this circumstance, it turns me to love solving algorithms from now on (laugh). Check it out! Problem You are given a very organized square of size N (1-based index) and a list of S commands The i th command will follow t...

A Template for Software Engineering Standards

Software engineering standard template A well-structured standard acts as a blueprint that guides engineers in their daily tasks and long-term goals. Below, I will outline a template for creating a comprehensive software engineering standard. Header The header serves as the document's identifier. It contains the following: Authors : The people who have contributed to the creation of the standard. Created Date : The date when the document was initially created. Version : The version of the standard. It is typically updated with significant changes. Status : The current status of the document, whether it's in draft, in-review, or official. Next Review Date : The date when the standard will be reviewed for relevancy and accuracy. Table of Contents A table of contents provides an overview of what the document contains, making it easier for readers to navigate through the document. Body The body of the standard comprises: Values : The core beliefs that guide the decision-maki...

MS SQL Server Views

"Creates a virtual table whose contents (columns and rows) are defined by a query. Use this statement to create a view of the data in one or more tables in the database. For example, a view can be used for the following purposes: - To focus, simplify, and customize the perception each user has of the database. - As a security mechanism by allowing users to access data through the view, without granting the users permissions to directly access the underlying base tables. - To provide a backward compatible interface to emulate a table whose schema has changed." [1] Beside that, our team used view in order to improve the performance of our web apps when a database has a very complicated relationship between its tables by using ORM Frameworks such as Hibernate. Example code: --create CREATE VIEW placeholders AS SELECT EMPKEY AS empkey, CONNUMB AS connumb, EMPNBR AS empNbr, ACEEMPN AS empFirstName, ACEEMPFN AS empLastName, EMPNAM AS empFullName, ...

vhandit

Search This Blog