Skip to main content

Java 8 - Persistent data structure


The following is a series of posts about "functional programming in Java" which is the result of my understanding by reading the book "Java 8 in Action: Lambdas, Streams, and Functional-style Programming, by Alan Mycroft and Mario Fusco".
1. Why functional programming?
2. Functional programming in Java 8
3. Java 8 - Using Functions as Values
4. Java 8 - Persistent data structure

Persistent data structure is also known as a simple technique but it's very important. Its other names are functional data structure and immutable data structure.

Why is it "persistent"?

Their values persist and are isolated from changes happening elsewhere. That's it!
This technique is described as below:

If you need a data structure to represent the result of a computation, you should make a new one and not mutable an existing data structure.

Destructive updates version
public static A doSomething(A a){
    a.setProp1("new value");
    return a;
}

Functional version
public static A doSomeThing(A a){
   A result = new A();
   result.setProp1(a.getProp1());
  return result;
}

Foo: If so, for what?
Bar: Imagine a case that you call the former method twice, the A is changed and affected by the latest call. Magic issue! Then, it's hard for maintenance, guy. Got it?

Reference

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

Comments

Post a Comment

Popular posts from this blog

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...

Make simple music program with beep(freq, duration) with Pascal

Pascal is my first programing language when I have studied in high school. It was really exciting for me. :) The Pascal programming language was created by Niklaus Wirth in 1970. It was named after Blaise Pascal, a famous French Mathematician. It was made as a language to teach programming and to be reliable and efficient. Pascal has since become more than just an academic language and is now used commercially . I tried to make a simple music program by using Lazarus IDE on MS Window 7, 64-bit. It frustrated me a few times how difficulty to use Sound command to make a sound. Sound did not work on my compiler and my platform anymore. So far, I just could use beep(freq, duration) from window unit to implement my work. Here is my code. ;) program mysong; uses Windows, crt; const C: Integer = 512; { x = A * EXP(LN(2)/12)} C_: Integer = 542; D: Integer = 574; D_: Integer = 608; E: Integer = 644; F: Integer = 682; F_: Integer = 723; G: Integer = ...

[Snippet] CSS - Child element overlap parent

I searched from somewhere and found that a lot of people says a basic concept for implementing this feature looks like below: HTML code: <div id="parent">  <div id="child">  </div> </div> And, CSS: #parent{   position: relative;   overflow:hidden; } #child{   position: absolute;   top: -1;   right: -1px; } However, I had a lot of grand-parents in my case and the above code didn't work. Therefore, I needed an alternative. I presumed that my app uses Boostrap and AngularJs, maybe some CSS from them affects mine. I didn't know exactly the problem, but I believed when all CSS is loaded into my browser, I could completely handle it. www.tom-collinson.com I tried to create an example to investigated this problem by Fiddle . Accidentally, I just changed: position: parent; to position: static; for one of parents -> the problem is solved. Look at my code: <div class="modal-body dn-placeholder-parent-positi...

Generating PDF/A From HTML in Meteor

My live-chat app was a folk of project Rocket.Chat which was built with Meteor. The app had a feature that administrative users were able to export the conversations into PDF files. And, they wanted to archive these files for a long time. I happened to know that PDF/A documents were good for this purpose. It was really frustrated to find a solution with free libraries. Actually, it took me more than two weeks to find a possible approach. TL, DR; Using Puppeteer to generate a normal PDF and using PDFBox to load and converting the generated PDF into PDF/A compliance. What is PDF/A? Here is a definition from Wikipedia: PDF/A  is an  ISO -standardized version of the  Portable Document Format  (PDF) specialized for use in the  archiving  and long-term  preservation  of  electronic documents . PDF/A differs from PDF by prohibiting features unsuitable for long-term archiving, such as  font  linking (as opposed to  font em...

The power of acceptance test

User Story is the place PO gives his ideas about features so that developers are able to know what requirements are. Acceptance tests are these show the most valuable things of the features represented by some specific cases. Usually PO defines them, but not always. Therefore, refining existing acceptance tests – even defining new ones that cover all features of the User Story must be a worth task. Acceptance test with Given When Then pattern If we understand what we are going to do, we can complete it by 50% I have worked with some members those just start implementing the features one by one and from top to down of the User Story description. Be honest, I am the one used to be. What a risky approach! Because it might meet a case that is very easy to miss requirements or needs to re-work after finding any misunderstood things. I have also worked with some members those accept spending a long time to clarify the User Story. Reading carefully of whole User Story by defining...