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Okay, raise your hand if you ever
received a null pointer exception.

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I see, every single one of you.

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Now keep your hands raised if you
are ever happy about that happening.

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Nobody.

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Null pointer exceptions happen when
you attempt to access a property or

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a method on an object, and that object
is in fact not there, it's null.

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So of course you can call a method like,
get first name on nothing.

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So a runtime exception is thrown.

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And you track the error through the code

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to find out that it's
possible that the object,

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the one that you so confidently trusted
in being there, actually isn't.

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So how do you know that
the value might not be there?

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Well, that's a great question.

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And the simple answer is this,
you actually don't.

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You have to trust your API
designer won't return a null or

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you have to be overprotective.

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You see this null protection
all over the place in code.

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You know the difference.

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Is this thing null?

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If so, throw in an exception.

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If not, everything's cool.

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Let's keep going.

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Now because some of these terminal
stream operations are known to maybe

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not return a value, Java 8 introduced
a new class called optional.

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They are intended to be used as
return values for methods only, and

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they represent the presence of a value or
the absence of a value.

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Now this is a common concept
in many programming languages,

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usually it's known as an option type.

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More frequently known as a maybe
type in functional programming.

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Check the teachers notes for
more information.

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By getting your hands on one of these
optionals, you know very clearly that

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there is a possibility that maybe
there isn't a value for you to access.

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Let's take a quick look at what we can
do with optionals that are returned

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from these terminal operation.

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>> So we've seen that aggregates like
max and min will return an option,

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because there's a chance
that there are no items.

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Remember what's the max of nothing?

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So using a similar thought
process let's write in,

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I'm feeling lucky style
search of the job titles.

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Now that's that google style of search
where you just return the first result

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00:02:04,028 --> 00:02:06,921
whose job title contains a specific word,
okay?

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00:02:06,921 --> 00:02:08,500
So let's write the search first.

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00:02:08,500 --> 00:02:10,600
So that would look like we have a stream,
right?

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00:02:11,830 --> 00:02:14,530
And we'll just use a simple filter, right?

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So we'll say filter,
we'll say where the job,

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where the getTitle contains Java.

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To make that whatever later.

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So there's a terminal operation
called findFirst which

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returns the first item that is found.

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Just like it says.

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okay, so let's use the intention action
here and let's see what it creates.

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So we'll introduce a local variable,
and it creates an option of jobs and

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we're gonna call it foundJob.

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Now let's go ahead and let's print
that out, so we'll print out foundJob.

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Cool, so the first job that I found is
from Business Intelli Solutions in Frisco,

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Texas.

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It's a junior Java job plus QE role.

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That sounds fun.

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QE being Quality Engineer.

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All right, so see how the job
variable is inside of an optional.

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Now that's because the value is present.

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In fact, there is a method on the optional
that lets us see if it is in fact present.

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So let's do that.

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We'll say foundJob and
this is an optional, isPresent.

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And if you want to get the value out of an
optional, you can just call get on it, so

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we'll say .get.

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And there so true, and you'll see
that it's no longer wrapped there.

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But what happens if the value isn't there?

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So let's see.

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Java is across just about every
industry that I can think of.

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So let's see if I can break it.

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I want the Java job in
the trampoline industry.

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So if we run it, boom.

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See how the isPresent is false, and
it's attempting to get an empty optional,

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throws a NoSuchElementException.

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Which is more or
less a null pointer exception.

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So as you can imagine you can deal with
this optional in an imperative way, right?

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I mean I could hypothetically put this
get here inside of an if statement.

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And I can check first to see if it's
present, just like our null pointer dance.

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But as you can probably imagine by now,
the optional

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actually has some great declarative
approaches to the problem space.

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So let's do this, let's go ahead and
turn this into a method.

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So we probably wanna have a variable, so
let's extract this variable out first.

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Let's do this.

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So I'm gonna use the action head.

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I'm gonna say extract variable, [LAUGH]
and it wants to call it trampoline.

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Let's call it searchTerm.

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Let's do that again.

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So I'm gonna take this trampoline and I'm
gonna refactor and extract the variable.

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I want the variable to
actually go outside.

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00:05:12,870 --> 00:05:15,690
So let's go ahead, we'll say that that's
fine, but I'm gonna move this up here.

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And now we don't need this anymore,
we don't need this, let's see if this will

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swing it to single lambda, there we go.

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And it's called,
we want this called search terms,

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and then we'll choose refactor rename.

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And a rename code
occurrences to searchTerm.

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Here we go.

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00:05:41,470 --> 00:05:46,180
And then we wanna turn this
whole thing here into a method.

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So let's do that.

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Let's do refactor and
we'll say extract method,

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00:05:54,080 --> 00:05:57,600
and we will call this LuckySearchJob.

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And yeah it's gonna take jobs and
it will take the search term, okay?

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00:06:07,449 --> 00:06:11,849
And if we switch this back to Java,
I'm gonna do a run,

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00:06:11,849 --> 00:06:14,540
cool, see it's still working.

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00:06:16,600 --> 00:06:21,572
So now that we're returning this search,
we can go ahead and

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we will say, make this an if.

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00:06:24,760 --> 00:06:27,560
So we'll say, if foundJob isPresent.

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Now we are safe to use the get here Right,
so we can safely use the get.

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00:06:36,870 --> 00:06:38,970
So that is what the null dance looks like.

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00:06:38,970 --> 00:06:43,300
Because we know that
this is gonna be here,

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00:06:43,300 --> 00:06:45,670
we can go ahead and
chain off of the outside of it.

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00:06:45,670 --> 00:06:47,150
So we know because it's present.

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00:06:47,150 --> 00:06:48,650
So now I can use getTitle.

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00:06:49,970 --> 00:06:52,760
And if I run this, there we go,

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00:06:52,760 --> 00:06:56,440
we'll just see that it is
printing out the title there.

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00:06:56,440 --> 00:06:58,730
So if we take a look at
this intention action here,

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it's gonna suggest something
that's kind of nice.

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00:07:00,590 --> 00:07:01,770
This is the declarative side.

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00:07:01,770 --> 00:07:06,204
It says replace optional
is present with ifPresent.

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00:07:06,204 --> 00:07:07,560
So let's go ahead and do that.

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00:07:07,560 --> 00:07:09,978
So ifPresent takes a consumer, right?

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00:07:09,978 --> 00:07:13,960
It takes a consumer, a consumer does this,
and this returns to nothing.

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00:07:13,960 --> 00:07:15,700
See how it takes whatever
value's passed in.

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This job here,
this will only be called if it's present.

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Otherwise, nothing will happen.

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So again, let's go ahead,
let's switch this back to trampoline.

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We run and nothing happens.

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00:07:30,280 --> 00:07:34,910
But sometimes you want to return a value
like if there isn't a value there at all.

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00:07:34,910 --> 00:07:39,040
Like in the case maybe I wanna
show no job found for instance.

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00:07:39,040 --> 00:07:41,990
So let's look at this imperatively first.

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00:07:41,990 --> 00:07:46,390
Let's switch this back to where we were.

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So that's imperatively.

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00:07:47,280 --> 00:07:55,634
So maybe, I would like to say,
else, No jobs found.

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00:07:55,634 --> 00:08:03,448
Let's run that and
then let's run trampoline, right?

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00:08:03,448 --> 00:08:05,770
And so it's gonna hit the other branch.

136
00:08:08,586 --> 00:08:09,330
No jobs found.

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00:08:10,510 --> 00:08:14,270
So declaratively,
options have some really nice methods.

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00:08:14,270 --> 00:08:15,590
So here, check this out.

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00:08:15,590 --> 00:08:21,370
Let's get rid of all of this and
we're gonna print out, foundJob.

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00:08:21,370 --> 00:08:28,775
Now this is an optional and optionals
have a map method, so let's do .map.

141
00:08:32,863 --> 00:08:34,820
And it works just like streams.

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00:08:34,820 --> 00:08:37,580
So we're gonna pass in
a method reference here.

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00:08:37,580 --> 00:08:42,110
So it's gonna get the title off
of that job should it exist.

144
00:08:42,110 --> 00:08:47,270
And just like we had before in the else,
there's a method called orElse

145
00:08:47,270 --> 00:08:52,070
which sounds a little
over the top like orElse.

146
00:08:52,070 --> 00:08:53,920
And then you'd have the value
that you'd like to show.

147
00:08:53,920 --> 00:08:55,660
So you say, No job found.

148
00:08:57,390 --> 00:09:00,340
Cool, so
once again if you get rid of this and

149
00:09:00,340 --> 00:09:03,760
you try to run it It's gonna
say optional empty, right?

150
00:09:03,760 --> 00:09:06,000
Because there's nothing for
it to do there.

151
00:09:06,000 --> 00:09:10,950
But if I drop the orElse, and

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00:09:10,950 --> 00:09:12,940
I don't know why this isn't
lining up it should be lining up.

153
00:09:17,127 --> 00:09:17,740
No jobs found.

154
00:09:22,470 --> 00:09:25,360
There are a bunch of different
functional approaches to dealing with

155
00:09:25,360 --> 00:09:27,430
optionals which make them quite nice.

156
00:09:27,430 --> 00:09:29,830
But it's also a bit misunderstood.

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00:09:29,830 --> 00:09:31,596
Check the teacher's notes for
more information.

158
00:09:31,596 --> 00:09:36,486
So the main trick to remember with
optionals is that if you're going to go

159
00:09:36,486 --> 00:09:40,574
the imperative route and
you call get yourself, remember,

160
00:09:40,574 --> 00:09:43,313
always check to see if is present first.

161
00:09:43,313 --> 00:09:46,873
Otherwise you'll end up causing the
equivalent of that null pointer exception

162
00:09:46,873 --> 00:09:48,980
that we've all learned to not love.

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00:09:48,980 --> 00:09:50,850
All right, so let's take a quick break and

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00:09:50,850 --> 00:09:55,940
then swing back to take a look at how
to let streams self generate for us.