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In order to start our journey on thinking
functionally, one really important concept

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to dial in on is the difference between
imperative and declarative coding styles.

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The imperative style focuses specifically
on how to perform the operations.

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Typically at a low level, taking
the system it is running on into account.

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Declarative style focuses more on

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what specifically you
are attempting to accomplish.

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The imperative style is definitely more
difficult to read as there are more lines

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of code and declarative is usually
very clear as to what is happening.

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Let's walk through an example one
that you've probably already seen and

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it will help demonstrate the differences.

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For those of you with people in your
lives that have food allergies,

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you know how difficult it is to
find something that they can eat.

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My daughter has an egg allergy.

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It's a bummer.

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It's pretty horrible.

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It seems like everything has eggs in it.

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Cupcakes, taffy, ice cream.

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You know, everything a kid likes to eat.

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Now as a parent,
I am constantly needing to check

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a list of ingredients to see
if it indeed contains eggs.

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Let's write a quick simulation
of this in code, in both styles.

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So here I have the current
version of IntelliJ IDEA open and

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I'm just going to make a new project.

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I'm gonna click create new project.

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Cool.
And I'm gonna just leave

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the defaults here.

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I'm gonna click next and I do want
to just make a quick command line.

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Let's go ahead and call this exploration.

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Okay so that's set everything up for us.

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Let's go ahead and let's start
write our code here and suggest it.

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Oops I indent with two space
I'm using the Google style.

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So we'll say list the string and
those are ingredients, right?

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And we'll make a new Arrays.asList.

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And we'll just go ahead and we'll
enter those guys, that's what we want.

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So let's see, we have flour,
what else do we have?

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We've got some salt.

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Delicious cupcakes here,
some baking powder, butter,

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I don't know how to cook really,
eggs and here comes the milk.

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All right, and
we will close off with a semicolon here.

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Okay, so let's solve our
issue of checking whether or

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not our ingredients has eggs, okay.

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I'm gonna go ahead and give us more space.

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Get rid of all the windows that are open,
here we go.

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Okay, so first things first.

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We'll need a variable to store our state,
right?

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So we'll wanna say boolean hasEggs,
and we'll just go ahead, and

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we don't know yet.

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We don't know if it has,
and so we said false.

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And now, what we wanna do is we wanna
loop through each of those ingredients.

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So we can do that by starting
to define a for loop, right?

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So we'll say for and
now we need another one of those temporary

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variables to store in the loop where
we're gonna currently process.

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So we'll say int i for index,
kind of standard thing there, right?

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And we'll make another temporary variable,
right?

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So now we've got 2, we've got hasEggs and
i, two temporary variables.

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And now we wanna make sure that we
go through all of the ingredients.

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So we wanna see if i is
less than the ingredients.

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And we wanna see if it's as
long as it is which was size.

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And we've gotta remember
that it's zero-based, right?

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It starts at zero, so it's gotta be less,

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not less than or equal to,
always have to think about that there.

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And then we're gonna go ahead and
we're gonna increment.

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Then we need to check if
that specific ingredient, so

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what we need to do is we
need to pull it out, right?

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We need to pull that one out.

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So we'll say String ingredient
equals ingredients.get, and

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we're gonna pass in that index that we've
been running through the loop with, right?

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Okay so then we wanna see does this
ingredient that we pulled out,

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does that equal eggs, right?

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Okay, and if it does we will for sure.

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We'll say hasEggs,
we're gonna set that to true.

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You know what since we
did know it hasEggs,

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we don't need to look at
the other stuff right?

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We can finish here, so
we can just go ahead and say break.

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Let's look at this code here for a second.

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That's a lot of code and brainpower needed
just to understand what's happening.

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Now we've done this a lot and
probably see code like this quite a bit.

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So it's probably feeling kind of familiar.

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But just imagine for
a second if you hadn't.

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There's a whole lot of what is
this doing going on, right.

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So now that we have our variable,
we can go ahead and see if it has eggs.

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Gotta break the news to my daughter and
say, sorry sweetheart.

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It has eggs.

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Sad face emoji.

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Now of course there's been
some evolution in looping.

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So we can of course clean up this
cognitive overload a little bit of all

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these things, right?

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So we can,
we can just go ahead we can say for

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the ingredients in ingredients, right?

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This enhanced for loop.

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So we can lose this index cause each one
is gonna have a specific time, right?

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We don't need to know how
long the list is anymore.

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This reads nicer, but
it's still an awful lot

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when all we really want to know is,
does ingredients contain eggs.

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We're still saying give me
each of the ingredients and

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I'll tell you when to stop.

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So the more declarative
way to ask this question,

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is just to ask the question, right?

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So, let's do this.

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If ingredients.contains,

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Eggs, Right?

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We don't need this.

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And there's nothing new here.

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Contains has been around since
the collections framework was introduced.

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But it's declarative.

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Look at how it explains what
it is that we're trying to do.

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It's not specifying how.

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Now this can be optimized
efficiently behind the scenes.

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And this is how it works
in the real world, right.

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If I'm at a restaurant, and
I wanna know about a possible cupcake for

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my daughter, I don't go, can you please
tell me every ingredient in this cupcake.

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Now don't worry I tell you
when to stop listing them and

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the case that I happen to hear
what I'm concerned about, right.

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I simply say, does this contain eggs?

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And the waiter or
waitress has their own method of knowing.

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How they get the answer isn't really
something I need to concern myself with.

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I'm really just concerned with
the answer to my question.

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So ready for it?

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This is the start of
the shift of your thinking.

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Functional programming is declarative.

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It'll take a little bit of shifting
in you programming mind, but

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we do it in real life.

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So it should feel more normal than how we
already force our imperative mind to work.

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One more example of how this looks
in something you've probably seen.

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In SQL or Structured Query Language.

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It's all declarative.

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Even if you haven't seen SQL before,
this is how you write the statements.

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The language allows you to declare

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very specifically what you
would like to get back.

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In this case, it's some specific fields
like first name, last name, and email.

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For a student with the id of 123.

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Notice how it doesn't specify how.

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This allows the database
to do whatever indexing or

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caching it needs on whatever platform that
implements the language specification.

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Let's stay in the declarative mindset and
introduce our first function.