1
00:00:00,590 --> 00:00:04,120
So we now have a couple of pretty
succinct ways to create and

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00:00:04,120 --> 00:00:06,420
pass functions into methods.

3
00:00:06,420 --> 00:00:09,530
Are you starting to get a sense
of how powerful this can be?

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00:00:09,530 --> 00:00:12,900
Are you noticing how it feels
just a little bit different?

5
00:00:12,900 --> 00:00:15,870
Well, that feeling is totally fine and
it's actually expected.

6
00:00:15,870 --> 00:00:18,780
Like we talked about,
this is a different way of thinking,

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00:00:18,780 --> 00:00:22,140
it's bound to feel a little bit strange,
especially at first.

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00:00:22,140 --> 00:00:25,790
We're about to go a little bit deeper now,
but the basic concepts are the same.

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00:00:26,870 --> 00:00:30,390
The main thing that I want you to know
is that you can provide a Lambda or

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00:00:30,390 --> 00:00:34,420
method reference anyplace these different
functional interfaces are expected.

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00:00:35,530 --> 00:00:38,490
And again,
the way these functional interfaces work

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00:00:38,490 --> 00:00:41,170
is that they have
a single abstract method.

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00:00:41,170 --> 00:00:45,100
As long as our Lambda, or
method reference, meet the signature

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00:00:45,100 --> 00:00:49,270
of the expected functional
interfaces method we can use it.

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00:00:49,270 --> 00:00:51,950
This method signature is also
known as a function shape.

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00:00:53,270 --> 00:00:56,690
I like to think of a function shape
as one of these little kid's toys

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00:00:56,690 --> 00:00:59,700
where you have these shapes that
need to fit into the specific holes.

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00:00:59,700 --> 00:01:03,070
The shape needs to line-up
to fit in specifically.

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00:01:03,070 --> 00:01:07,060
Now, so far we've only looked at
one type of function shape, and

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00:01:07,060 --> 00:01:08,470
that is the Consumer.

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00:01:08,470 --> 00:01:12,650
Out of the box there are quite a few of
these function shapes that Java offers.

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00:01:12,650 --> 00:01:16,640
Each of these function shapes
have a pretty specific use case.

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00:01:16,640 --> 00:01:20,050
In my experience,
most of the problems that we encounter

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00:01:20,050 --> 00:01:23,840
can be solved with the defaults provided
in the Java.util.function package.

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00:01:25,150 --> 00:01:28,250
So I want to take a moment with you and
explore the documentation.

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00:01:28,250 --> 00:01:32,520
We'll review the Consumer and then go over
the three other basic function shapes.

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00:01:33,600 --> 00:01:37,342
Okay, so I'm gonna go and search for

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00:01:37,342 --> 00:01:41,706
Java.util.function and then package.

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00:01:43,833 --> 00:01:45,510
And it's gonna bring up this right here.

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00:01:45,510 --> 00:01:47,400
This is the official help, so

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00:01:47,400 --> 00:01:51,250
this package contains some more
specialized versions of the basics.

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00:01:51,250 --> 00:01:56,140
So, for instance, this first one
here is our friend Consumer, right?

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00:01:56,140 --> 00:02:01,470
But as you can see it accepts two
parameters, so it's called a BiConsumer.

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00:02:01,470 --> 00:02:03,350
So to get started looking in here,

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00:02:03,350 --> 00:02:06,600
let's look at one that we're familiar
with, our old friend Consumer.

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00:02:06,600 --> 00:02:07,210
Let's take a look.

37
00:02:07,210 --> 00:02:10,960
So down here in Consumer,
It says, represents an operation

38
00:02:10,960 --> 00:02:14,690
that accepts a single input argument and
returns in the result.

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00:02:14,690 --> 00:02:16,240
It's exactly what we were working with.

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00:02:16,240 --> 00:02:17,257
So let's click into it.

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00:02:19,364 --> 00:02:21,696
So if we scroll down a little
bit here to the methods,

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00:02:21,696 --> 00:02:23,130
we can see the different types.

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00:02:23,130 --> 00:02:27,380
And if we click in here under
Abstract Methods, you can see the single

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00:02:27,380 --> 00:02:31,280
Abstract Method that we were talking
about, which we know is called accept.

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00:02:31,280 --> 00:02:34,570
Now its signature requires a type of T,

46
00:02:34,570 --> 00:02:38,280
which if we look up here it says the type
of input to the operation, right?

47
00:02:38,280 --> 00:02:41,680
So in our case this T was a string and
it returns nothing, right?

48
00:02:41,680 --> 00:02:42,710
It returns a void.

49
00:02:42,710 --> 00:02:46,420
Now we know that we could use this
with a forEach on iterables because,

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00:02:46,420 --> 00:02:48,150
well, we just used it.

51
00:02:48,150 --> 00:02:52,100
But what if we wanted to see where
this was used elsewhere in the JDK?

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00:02:52,100 --> 00:02:56,020
Now, when learning how to use different
tools I find it super helpful

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00:02:56,020 --> 00:02:58,400
to see some examples of
how it's being used.

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00:02:58,400 --> 00:03:02,570
There's a handy little tab at
the top of Java docs called Use.

55
00:03:02,570 --> 00:03:04,250
So let's do that, let's click Use.

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00:03:04,250 --> 00:03:07,874
Or you can [LAUGH] also read this as use,

57
00:03:07,874 --> 00:03:12,081
like show me some use for
this, either way.

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00:03:12,081 --> 00:03:15,854
All right, so here it shows
Packages that use Consumer and

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00:03:15,854 --> 00:03:19,400
here's places where it's
being used as a parameter.

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00:03:19,400 --> 00:03:23,420
So we'll see here that forEach
uses a Consumer, just like we saw.

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00:03:23,420 --> 00:03:25,550
I find this super handy when
you're trying to learn something.

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00:03:25,550 --> 00:03:28,010
So let's pop back to the Package level,
so we'll click Package.

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00:03:29,250 --> 00:03:32,576
All right, so let's pick up on
our next functional interface.

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00:03:32,576 --> 00:03:36,689
Let's scroll down here and
take a look at Supplier,

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00:03:36,689 --> 00:03:39,500
represents a supplier of results.

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00:03:39,500 --> 00:03:40,610
Thanks a lot.

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00:03:40,610 --> 00:03:42,890
Let's dive in.

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00:03:42,890 --> 00:03:46,475
Okay, and we'll go down and we'll take
look at the single Abstract Method,

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00:03:46,475 --> 00:03:47,915
it's just called get.

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00:03:47,915 --> 00:03:50,370
Okay, so it gets a result.

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00:03:50,370 --> 00:03:55,010
So it doesn't take any parameters and
it returns a type of T,

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00:03:55,010 --> 00:03:59,870
which in this case is the type of
result supplied by this supplier.

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00:03:59,870 --> 00:04:03,760
So this function will supply
its caller with a value.

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00:04:03,760 --> 00:04:06,810
Now note, this is a different
shape than the Consumer.

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00:04:06,810 --> 00:04:11,300
Our Consumer is a function that consumed
an object and did some stuff but

76
00:04:11,300 --> 00:04:12,540
didn't return anything.

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00:04:12,540 --> 00:04:16,110
This supplier, when implemented,
won't actually take anything,

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00:04:16,110 --> 00:04:19,060
it just returns, it supplies something.

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00:04:19,060 --> 00:04:21,490
This is handy in places where
you want an object, and

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00:04:21,490 --> 00:04:23,330
you don't really care how it's created.

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00:04:23,330 --> 00:04:25,740
Supplies, here's your birthday cake.

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00:04:25,740 --> 00:04:27,350
Sorry, that was a dumb joke.

83
00:04:27,350 --> 00:04:28,750
No supplies there.

84
00:04:28,750 --> 00:04:29,930
Man, that double.

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00:04:29,930 --> 00:04:34,190
So the way that these functional
interfaces are named, Consumer and

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00:04:34,190 --> 00:04:37,651
Supplier, describes how they
are expected to be used.

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00:04:37,651 --> 00:04:42,748
Now speaking of being used,
let's click the Use tab again up here.

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00:04:42,748 --> 00:04:49,540
So let's scroll down and let's take a look
at Methods with parameters of type.

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00:04:49,540 --> 00:04:51,530
Let's take a look at this one here,
this is a pretty fun one.

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00:04:51,530 --> 00:04:55,560
This is called Objects.requireNonNull.

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00:04:55,560 --> 00:05:01,140
So if we click into here, we can see
that this was introduced in 1.8 or

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00:05:01,140 --> 00:05:02,500
Java 8, as we call it.

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00:05:02,500 --> 00:05:06,300
So it's a helper method that you can
use to make sure that your parameters

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00:05:06,300 --> 00:05:10,600
are not null and it actually throws
a null pointer exception for you.

95
00:05:10,600 --> 00:05:12,680
It kind of wraps up all
that ceremony we do, right?

96
00:05:12,680 --> 00:05:16,610
Like if object is null, then throw a new
illegal argument exception sort of thing,

97
00:05:16,610 --> 00:05:17,840
kind of wraps that all up.

98
00:05:17,840 --> 00:05:21,060
It's a customized null pointer exception.

99
00:05:21,060 --> 00:05:22,270
So it's pretty straightforward, right?

100
00:05:22,270 --> 00:05:23,590
You just give it an object, and

101
00:05:23,590 --> 00:05:27,300
then you give it a supplier,
the second parameter, right?

102
00:05:27,300 --> 00:05:31,560
This is similar to how the forEach
method expected a Consumer.

103
00:05:31,560 --> 00:05:35,590
This requireNonNull
method expects a Supplier.

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00:05:35,590 --> 00:05:37,450
So let's use it, right?

105
00:05:37,450 --> 00:05:39,280
Let's flip back to our code.

106
00:05:39,280 --> 00:05:41,490
And let's do it in this yell method here,
right?

107
00:05:41,490 --> 00:05:47,340
So make sure that words comes
in always non null, right?

108
00:05:47,340 --> 00:05:48,855
And actually let's do this.

109
00:05:48,855 --> 00:05:51,520
Let's imagine a feature request came in.

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00:05:51,520 --> 00:05:57,320
And the object here was to create an issue
in our bug tracker system every time that

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00:05:57,320 --> 00:06:02,470
yell is called with a null value, so that
we could try to stop that from happening.

112
00:06:02,470 --> 00:06:05,380
You don't want anybody to
yell without any words.

113
00:06:05,380 --> 00:06:10,250
So what we'll do is if it is null we'll
open up an issue in a bug tracking system.

114
00:06:10,250 --> 00:06:11,080
Sound good?

115
00:06:11,080 --> 00:06:11,810
So let's do it.

116
00:06:11,810 --> 00:06:17,646
So we will say Objects.requireNonNull.

117
00:06:17,646 --> 00:06:20,713
And we're gonna check here on words first.

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00:06:20,713 --> 00:06:23,334
We'll see that it wants a Supplier.

119
00:06:24,891 --> 00:06:26,630
Cuz it's an overloaded method.

120
00:06:26,630 --> 00:06:29,070
One takes string and one takes a Supplier.

121
00:06:29,070 --> 00:06:33,080
Now these Suppliers are great because
they're what's known as lazy.

122
00:06:33,080 --> 00:06:37,920
The Supplier will only be called
when words here, when this is null.

123
00:06:37,920 --> 00:06:40,570
Otherwise it's just a function
waiting to be called.

124
00:06:40,570 --> 00:06:44,330
But it's not going to do anything just yet
because it's lazy.

125
00:06:44,330 --> 00:06:48,110
So we need to add a Supplier here,
so let's put a Lambda in place.

126
00:06:48,110 --> 00:06:52,220
So what I'll do is I'll open
the parentheses like we know, now.

127
00:06:52,220 --> 00:06:55,930
[SOUND] It doesn't have any parameters,
so what do I do?

128
00:06:55,930 --> 00:06:59,270
Well, the answer is this,
you just leave the parens.

129
00:06:59,270 --> 00:07:01,760
Just like when you call a method
that doesn't take any parameters.

130
00:07:01,760 --> 00:07:04,070
It's just opened and
closed, just like that.

131
00:07:04,070 --> 00:07:06,720
Okay, and
then we need to do the body, right?

132
00:07:08,150 --> 00:07:11,910
What we want over here, is we want to
return a string that will be used for

133
00:07:11,910 --> 00:07:14,750
the null pointer exceptions message, okay?

134
00:07:14,750 --> 00:07:18,600
So what's gonna happen is when this
is missing it's going to try to

135
00:07:18,600 --> 00:07:19,760
get this message.

136
00:07:19,760 --> 00:07:22,090
So we'll just keep this on a single line,
right?

137
00:07:22,090 --> 00:07:25,200
So there's no need for the open bracket.

138
00:07:25,200 --> 00:07:28,500
One more sugary nicety
of a single line Lambda

139
00:07:28,500 --> 00:07:31,390
is the return keyword is always assumed.

140
00:07:31,390 --> 00:07:33,940
So I can just put what I
want to have returned here.

141
00:07:33,940 --> 00:07:36,640
So, let's see,
that would look something like this.

142
00:07:36,640 --> 00:07:44,170
Let's say that we want it to say Created
Issue and then we'll make up a method.

143
00:07:45,490 --> 00:07:46,777
We'll just talk about a method.

144
00:07:46,777 --> 00:07:50,421
Andd so we'll say Main.,
let's call it createIssue.

145
00:07:50,421 --> 00:07:52,379
It'll be a static method.

146
00:07:52,379 --> 00:07:55,430
It doesn't exist, but
we'll do that for now.

147
00:07:57,010 --> 00:07:57,510
And let's see.

148
00:07:58,780 --> 00:08:02,020
So we'll create the create method issue.

149
00:08:03,200 --> 00:08:05,600
And in here we'll just fake an API call.

150
00:08:05,600 --> 00:08:09,994
We'll say something like Some

151
00:08:09,994 --> 00:08:15,068
external API call to a bug tracker.

152
00:08:15,068 --> 00:08:18,548
And we could imagine that that would
happen, is it would go out call,

153
00:08:18,548 --> 00:08:21,330
create a ticket, and
it would return some sort of ID.

154
00:08:21,330 --> 00:08:23,790
So we'll just pretend for right now

155
00:08:23,790 --> 00:08:28,730
that this is some sort of ID to our bug
tracking system so we can find issues.

156
00:08:28,730 --> 00:08:33,130
So since this method is expensive, right,
tt's gonna go out and do this API call,

157
00:08:33,130 --> 00:08:34,640
we don't want this to happen all the time.

158
00:08:34,640 --> 00:08:39,460
And we're leaning on the laziness of
the requireNonNull method, right?

159
00:08:39,460 --> 00:08:43,550
Keeping all of this execution, all of this
stuff in here is inside of the Supplier.

160
00:08:43,550 --> 00:08:46,100
It's only gonna happen when this is null.

161
00:08:47,250 --> 00:08:50,810
So if we come down here to the end,
we can actually now make it fail, right?

162
00:08:50,810 --> 00:08:54,890
So we'll say Main.yell,
now I'm gonna pass in a null.

163
00:08:56,680 --> 00:08:57,623
Then we run it.

164
00:09:00,993 --> 00:09:06,229
And bam, some external call to a bug
tracking system and we'll see up here

165
00:09:06,229 --> 00:09:11,137
in the NullPointerException that
it says Created issueABC123.

166
00:09:11,137 --> 00:09:12,374
Pretty powerful?

167
00:09:12,374 --> 00:09:15,638
We'll dive deeper into the laziness
concept here in a bit and

168
00:09:15,638 --> 00:09:18,646
in fact I'm gonna go park that
term just to make sure that

169
00:09:18,646 --> 00:09:21,158
we don't forget about
talking about it more.

170
00:09:21,158 --> 00:09:24,220
So let's do that,
here we're gonna add lazy.

171
00:09:24,220 --> 00:09:28,810
This seems like a pretty good time to take
a little break before we dive back into

172
00:09:28,810 --> 00:09:30,820
the remaining basic function shapes.