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<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no">
<title>RxJava</title>
<link rel="stylesheet" href="css/reveal.css">
<link rel="stylesheet" href="css/theme/black.css">
<!-- Theme used for syntax highlighting of code -->
<link rel="stylesheet" href="lib/css/zenburn.css">
<!-- Printing and PDF exports -->
<script>
var link = document.createElement( 'link' );
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = window.location.search.match( /print-pdf/gi ) ? 'css/print/pdf.css' : 'css/print/paper.css';
document.getElementsByTagName( 'head' )[0].appendChild( link );
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</head>
<body>
<div class="reveal">
<div class="slides">
<section data-markdown>
<textarea data-template>
# RxJava
## A simple introduction to RxJava and how it can help your application
</textarea>
</section>
<section>
<h2>Links</h2>
<ul>
<li><a href="http://palhargitai.github.io/rxjava-presentation/">This presentation online</a></li>
<li><a href="https://github.com/palhargitai/rxjava-examples">Code samples online</a></li>
<li><a href="https://github.com/ReactiveX/RxJava">RxJava site</a></li>
<li><a href="http://rxmarbles.com">Rx usecase demo</a></li>
</ul>
</section>
<section data-markdown>
<textarea data-template>
## Todays goals to understand:
* what RxJava is
* how and when to apply it
* that it's not magic or an end-all solution
* that it _can_ help improve user experience and memory performance
</textarea>
</section>
<section data-markdown>
<textarea data-template>
## What is RxJava
from [the github repo](https://github.com/ReactiveX/RxJava):
RxJava – Reactive Extensions for the JVM – a library for composing asynchronous and event-based programs using observable sequences for the Java VM.
</textarea>
</section>
<section data-markdown>
<textarea data-template>
What we used to do:
```
public List<String> getIds() {
List<Entity> entities = dao.getEntities();
List<String> result = new ArrayList<>(entities.size());
for (Entity entity : entities) {
result.add(entity.getid());
}
return result;
}
```
or:
```
public List<String> getIds() {
return dao.getEntities().stream().map(Entity::getId).toList();
}
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
What we can now do:
```
public Flowable<String> getIds() {
return dao.getEntities().map(Entity::getId);
}
```
## Why would this be better?
</textarea>
</section>
<section data-markdown>
<textarea data-template>
Looking back:
```
List<String> result = new LinkedList<>();
for (Entity e: dao.getEntities()) {
/* We retrieve all entities in 1 go, *
* this means that we're waiting for the *
* method to return only after getting _all_ *
* the data... */
result.add(e.getId());
}
return result;
/* By now we've used memory for all the entities *
* as well as memory for all the ids. */
}
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
Looking forward:
```
public Flowable<String> getIds() {
return dao.getEntities().map(Entity::getId);
}
```
What this returns is a _possible_ execution. This will only execute
when we actually subscribe to the data. Then it'll be pulled through
the observable sequence.
See example 1.
</textarea>
</section>
<section data-markdown>
<textarea data-template>
## Memory and CPU usage
Assume that each operation takes 10(ms?) and each entity uses 10(kb?) memory,
and an ID uses 5(kb?) memory. We can make this in to a graph. Let's first look
at the whole chain for one entity could look like:
```
Entity e = nextEntity();
String result = e.getId();
addIdToView(result);
```
30ms for one entity
times 10 entities is 300ms in total.
(10 entities `* 10kb) + (10 ids `* 5kb) is 150kb in total.
</textarea>
</section>
<section data-markdown>
<textarea data-template>
Old style:
```
Entity entity01 = nextEntity();
Entity entity02 = nextEntity();
....
Entity entity10 = nextEntity();
String id01 = entity01.getId();
....
String id10 = entity10.getId();
addIdToView(id01);
....
addIdToView(id10);
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
New style:
```
Entity entity01 = nextEntity();
String id01 = entity01.getId();
addIdToView(id01);
Entity entity02 = nextEntity();
String id02 = entity02.getId();
addIdToView(id02);
....
Entity entity10 = nextEntity();
String id10 = entity10.getId();
addIdToView(id10);
```
</textarea>
</section>
<section>
<h2>Memory usage</h2>
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<section>
<h2>Response Times</h2>
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## Short Summary so far
* Only use the memory you need at the time,
* First element is shown much faster, better response times,
* Not magic, software does not become faster, (for the user it does though!).
</textarea>
</section>
<section data-markdown>
<textarea data-template>
## Operators!
* map, filter, cast,
* first, last, skip, take,
* toList, toMap,
* every, any, count, contains, distinct, etc.
See example 2.
</textarea>
</section>
<section data-markdown>
<textarea data-template>
## Common Traps
* **Failure to subscribe** (See example 3)
* Failure to 'think reactive'
* Sync behaviour
</textarea>
</section>
<section data-markdown>
<textarea data-template>
# Questions so far?
</textarea>
</section>
</div>
</div>
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// - https://github.com/hakimel/reveal.js#configuration
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