Stateless vs Stateful

Question

I'm interested in articles which have some concrete information about stateless and stateful design in programming. I'm interested because I want to learn more about it, but I really can't find any good articles about it. I've read dozens of articles on the web which vaguely discuss the subject, or they're talking about web servers and sessions - which are also 'bout stateful vs stateless, but I'm interested in stateless vs stateful design of attributes in coding. Example: I've heard that BL-classes are stateless by design, entity classes (or at least that's what I call them - like Person(id, name, ..)) are stateful, etc.

I think it's important to know because I believe if I can understand it, I can write better code (e.g. granularity in mind).

Anyways, really short, here's what I know 'bout stateful vs stateless:

Stateful (like WinForms): Stores the data for further use, but limits the scalability of an application, because it's limited by CPU or memory limits

Stateless (Like ASP.NET - although ASP tries to be stateful with ViewStates): After actions are completed, the data gets transferred, and the instance gets handed back to the thread pool (Amorphous).

As you can see, it's pretty vague and limited information (and quite focussed on server interaction), so I'd be really grateful if you could provide me with some more tasty bits of information :)

Answer 1

Stateless means there is no memory of the past. Every transaction is performed as if it were being done for the very first time.

Stateful means that there is memory of the past. Previous transactions are remembered and may affect the current transaction.

Stateless:

// The state is derived by what is passed into the function  function int addOne(int number) {     return number + 1; } 

Stateful:

// The state is maintained by the function  private int _number = 0; //initially zero  function int addOne() {    _number++;    return _number; } 

Refer from: https://softwareengineering.stackexchange.com/questions/101337/whats-the-difference-between-stateful-and-stateless

Answer 2

A stateful app is one that stores information about what has happened or changed since it started running. Any public info about what "mode" it is in, or how many records is has processed, or whatever, makes it stateful.

Stateless apps don't expose any of that information. They give the same response to the same request, function or method call, every time. HTTP is stateless in its raw form - if you do a GET to a particular URL, you get (theoretically) the same response every time. The exception of course is when we start adding statefulness on top, e.g. with ASP.NET web apps :) But if you think of a static website with only HTML files and images, you'll know what I mean.