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API stands for "Application Programming Interface", and believe it or not, we are already using them. But what exactly does that mean, and what about APIs over the web?
Definitions
- API: Application Programming Interface - the interface through which an SDK or system is used by our code
- SDK: Software Development Kit - all the pieces required for a software system
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Not so long ago making our weather app or
frankly, many websites,
0:00
apps, or services, would have been
incredibly challenging because
0:05
access to unified weather
data wasn't available.
0:09
We would of had to go through the
cumbersome task of pulling data together
0:13
from different sources.
0:17
Imagine trying to get temperature,
humidity, precipitation, and
0:18
more from locations all over the world.
0:23
[SOUND] What a task.
0:25
Fortunately for us, someone else
has already tackled this task and
0:28
made the information
available through a service.
0:32
Better yet, it's free for small apps, and
0:36
if our app goes viral,
the fee still isn't too large.
0:39
We take another look at darksky.net,
scroll back down to our Dark Sky API link.
0:44
Scroll down just a little bit here,
there's a learn more button.
0:51
Here we're taken to a page that tells
us about the API and how we can use it.
0:57
What exactly is an API though?
1:01
API stands for
application programming interface.
1:04
It's the interface we use to write
code against all sorts of systems.
1:08
We've actually been working
with APIs all along.
1:13
For example, in previous Android courses,
1:16
we used Android APIs to interact
with activities, views, and buttons.
1:19
When we look at documentation for a class,
1:24
we're looking at
the Android API reference docs.
1:27
An API is literally the interface used
by our code to interact with the system.
1:30
These interfaces can be
a separate third party system,
1:35
like Dark Sky, or
smaller subsystems in Android.
1:39
Such as the parts involved to
determine our physical location.
1:42
Although it may seem very different to us,
using a third party API is very similar to
1:46
using the Android APIs we're
already comfortable with.
1:51
Our interactions with a third party
API will just be slightly different.
1:54
We'll also need to discover what's
available for us from the API.
1:59
Before we jump into that though,
let's take a few moments to talk about
2:04
the concept of an interface in
application programming interface.
2:08
In different fields people
use the term black box,
2:13
to refer to a thing that does some work
that we can't see from the outside.
2:16
A black box, in this context,
is simply something that we,
2:21
as developers,
don't need to concern ourselves with.
2:24
Let's think outside
the world of programming and
2:28
use a bakery as an example.
2:31
The bakery's sous chef is looking
at a recipe for a particular item.
2:32
She goes out to the market,
purchases the ingredients, and
2:36
delivers them back to the bakery.
2:40
The bakery is our black box.
2:42
As far as we're concerned,
ingredients go into the bakery and
2:44
come out as a delicious baked item.
2:48
For example, our bakery gets an order for
a specific cake, a gateau fraisier.
2:50
If our sous chef brings eggs,
flour, sugar, baking powder, cream,
2:56
milk, vanilla, almond paste, and
strawberries from the market,
3:01
we can expect to get the classic
french strawberry cake.
3:06
We aren't necessarily concerned with
how this particular bakery goes about
3:10
producing the final product.
3:14
We don't need to know their exact
procedure for making the sponge cake,
3:16
pastry cream, etc,
as long as the output the gateau fraisier,
3:21
is an agreed upon outcome by
both the bakery and customer.
3:24
Similarly, if this particular bakery
goes out of business, we can replace
3:28
this bakery with another one, and
should expect to get the same product.
3:32
This is similar in nature to how
things are modeled with an API.
3:37
We provide a service some inputs,
our ingredients,
3:40
to the API, the bakery in our example.
3:44
Which does some work and
provides us with some output, our cake.
3:46
How does this help us as developers,
though?
3:50
Let's imagine that in our application,
3:53
we have a method that handles getting us
a strawberry cake called getGateauFraise.
3:56
Whenever we want to get some cake,
we call the method,
4:01
which handles how we go about this.
4:04
If we had been using Gabriel's Bakery for
our cake, and then, for
4:06
whatever reason,
we want to change it to Louie's bakery,
4:10
we can do that inside our
getGateauFraise method.
4:13
We can still call and use it the same
way without changing our inputs, and
4:16
still get the same outputs.
4:20
Pretty convenient and powerful, right?
4:22
This makes code and project maintenance,
well, a piece of cake.
4:24
Let's think of a truly different idea.
4:29
We could change the getGateauFraise method
to interface with a 24th-century food
4:31
replicator, to get
an instantaneous strawberry cake.
4:36
Okay, that's a bit out of this world, but
4:39
it shows the power of
the interface concept.
4:41
We don't need to change anything
with our inputs and outputs, but
4:44
the work being done inside
the black box is very different.
4:48
The best part?
4:51
The rest of our code doesn't care.
4:52
Okay, let's get back to reality a bit.
4:55
Forget about our food replicator and,
sadly, cake altogether, and
4:57
get back to grabbing data from the web.
5:02
In programming, this black box concept
shows up in a lot of different ways.
5:04
A well-designed system is programmed so
5:09
that the interfaces between
components are clearly defined.
5:12
Each component then can look,
and act, like a black box for
5:16
the other parts of the system.
5:20
let's change this diagram to reflect what
we'll be building in stormy with Dark Sky.
5:22
We'll utilize the Dark Sky API and
pass in an API key,
5:27
along with a location as our input.
5:31
Our black box then will be
a getForecast method, and
5:34
that method will get the forecast
from the internet and
5:37
output the forecast data to use and
display in our app.
5:40
Actually, there are two important
interfaces at work here.
5:44
The first is the interface
of the getForecast method,
5:47
which includes the properties we'll need.
5:51
The second interface, is actually between
getForecast and the Dark Sky API,
5:53
this is what's known as a web interface.
5:58
One last thing to mention here, hopefully
it provides some additional clarity.
6:01
We also talk about the Android SDK,
or software development kit.
6:06
What's the difference between an SDK and
an API?
6:10
Well, an API is part of an SDK.
6:14
Recall that a API is just the interface,
6:16
the interface to the rest of
the SDK where all the work is done.
6:20
The API is the way in which
you use something, and
6:24
the SDK is where the work is accomplished.
6:27
Sometimes we use an API alone
without any access to the underlying
6:30
components of the SDK.
6:34
Which is what we're doing when we
request data from the Dark Sky API.
6:36
We simply make a request to their
interface without needing anything else.
6:40
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