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Okay, so we've got to look at consumer and
supplier.

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00:00:04,680 --> 00:00:08,210
So next up in our list of
important function shapes

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00:00:08,210 --> 00:00:11,420
is the root of all of these, function.

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00:00:11,420 --> 00:00:14,610
Now, it gets a little bit weird
when we start looking at this.

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00:00:14,610 --> 00:00:18,700
So this represents a function that accepts
a one argument and produces a result.

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00:00:18,700 --> 00:00:24,470
So we're gonna click into here and
this is a function functional interface.

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00:00:24,470 --> 00:00:25,630
It gets a little weird talking about it.

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00:00:25,630 --> 00:00:27,900
Don't worry, I didn't pick up a stutter.

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00:00:27,900 --> 00:00:33,530
So, a function takes a single argument and
produces a result.

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00:00:33,530 --> 00:00:38,190
And both the parameter type and
the return value are specified, right?

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00:00:38,190 --> 00:00:40,047
That's what the T and the R are.

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00:00:40,047 --> 00:00:44,912
So T is the type that's passed in and
R is the result type.

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00:00:44,912 --> 00:00:46,353
So let's swing down.

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00:00:46,353 --> 00:00:50,250
Let's take a look at the single
abstract method and it's called apply.

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00:00:50,250 --> 00:00:54,570
So again, it accepts a T and
it returns an R.

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00:00:54,570 --> 00:00:59,350
So, when you define the function,
you specify what type it expects and

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00:00:59,350 --> 00:01:01,510
then the type of the return value.

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00:01:01,510 --> 00:01:03,980
So as you can imagine, these are great for

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00:01:03,980 --> 00:01:08,620
transforming values from one to
another and going between types.

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00:01:08,620 --> 00:01:12,570
They both can be strings but
you can switch between types.

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00:01:12,570 --> 00:01:15,640
We'll get our feet wet with these here
in a bit when we explore streams.

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00:01:15,640 --> 00:01:19,580
Another thing that I wanted to point out
here in the docs, while we're here.

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There are these things called default
methods which are new to java eight

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00:01:24,320 --> 00:01:27,630
interfaces and they allow you to
change several functions together.

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00:01:27,630 --> 00:01:31,560
So if we click here, if we click this
default methods, we'll see that you can go

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00:01:31,560 --> 00:01:34,480
on every function that has this
method that says andThen and

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00:01:34,480 --> 00:01:36,780
you can pass in a function okay.

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00:01:36,780 --> 00:01:40,440
So you can kind of chain several
of these functions together.

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00:01:40,440 --> 00:01:43,120
You call your function and
then call another and then another and

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00:01:43,120 --> 00:01:45,300
it just sort of goes flowing between them.

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00:01:45,300 --> 00:01:50,350
This is called functional composition and
as you guessed, I'm gonna go ahead and

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00:01:50,350 --> 00:01:51,830
park that right now.

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00:01:51,830 --> 00:01:54,610
Let's flip over and let's write that here.

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00:01:54,610 --> 00:01:57,080
We'll write functional composition.

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00:01:57,080 --> 00:02:01,479
We are getting a pretty healthy looking
list for the parking lot there.

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00:02:01,479 --> 00:02:06,145
Can't wait to go over this stuff, but
we'll get to it in a bit, don't worry.

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00:02:06,145 --> 00:02:07,665
So about these default methods,

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00:02:07,665 --> 00:02:11,042
check the teacher's notes if it needs
some more information about that.

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00:02:11,042 --> 00:02:12,437
Other super powerful and

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00:02:12,437 --> 00:02:18,070
there's a couple of these interfaces that
have some pretty handy default methods.

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00:02:18,070 --> 00:02:23,930
Okay and last but definitely not least,
let's check out Predicate.

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00:02:25,950 --> 00:02:27,830
Predicate is our shape here,

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00:02:27,830 --> 00:02:32,580
and it represents a Predicate, thank you,
boolean-valued function of one argument.

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00:02:34,130 --> 00:02:39,190
So what happens here is if we look at
this abstract method, it has an abstract

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00:02:39,190 --> 00:02:44,020
method of name test and it will take
a type t and always return true or

46
00:02:44,020 --> 00:02:49,030
false so it's really kind of a specific
type of function right, of the function,

47
00:02:49,030 --> 00:02:55,040
functional interface so it will take
a type and return a true or false.

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00:02:55,040 --> 00:02:55,780
Pretty nice, right?

49
00:02:55,780 --> 00:02:57,490
It's very specific.

50
00:02:57,490 --> 00:03:00,740
So, just like functions,
it has a default method and

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00:03:00,740 --> 00:03:02,080
you can kind of chain these together.

52
00:03:02,080 --> 00:03:08,410
So you can say, this and this or not this,
so you can negate it or do an or.

53
00:03:08,410 --> 00:03:12,120
We'll get our hands wet with
these real soon as we use these

54
00:03:12,120 --> 00:03:14,980
often when trying to filter values.

55
00:03:14,980 --> 00:03:19,150
The java.util.function package has
some wonderful functional interfaces

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00:03:19,150 --> 00:03:22,320
that we can lean on when diving
deeper into functional programming.

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00:03:22,320 --> 00:03:25,360
I'm glad you got a chance to see how
to explore the out of the box options.

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00:03:26,480 --> 00:03:29,250
Let's review the four basic
shapes that I'd like you to be

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00:03:29,250 --> 00:03:30,500
familiar with real quick.

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00:03:30,500 --> 00:03:35,250
Consumer, a function that accepts
something and returns nothing.

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00:03:35,250 --> 00:03:38,350
These are useful when you need to
be provided a value in context.

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00:03:39,590 --> 00:03:43,420
Supplier, this accepts nothing but
returns a value.

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00:03:43,420 --> 00:03:47,740
This is great when you need something
initially, like we did in our yell method.

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00:03:47,740 --> 00:03:51,690
Function, this takes a single argument,
and returns a value.

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00:03:51,690 --> 00:03:54,200
This is great for transformation.

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00:03:54,200 --> 00:03:56,670
And Predicate accepts a parameter, and

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00:03:56,670 --> 00:04:00,550
returns a boolean value,
helpful when filtering value.

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00:04:00,550 --> 00:04:05,023
You probably noticed that the remaining
functional interfaces in the package were

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00:04:05,023 --> 00:04:07,039
either a typed version of those four or

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00:04:07,039 --> 00:04:11,075
a version that changes the amount of
parameters that the function accepts.

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00:04:11,075 --> 00:04:15,730
The amount of parameters that a function
accepts is referred to as parity.

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00:04:15,730 --> 00:04:19,740
If it helps, I remember the bi prefix
like the bicycle, like two wheels,

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00:04:19,740 --> 00:04:21,730
like this bike here, two wheels.

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00:04:21,730 --> 00:04:25,720
Now, that is versus the uni prefix
like unicycle which means one wheel.

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00:04:26,920 --> 00:04:30,060
So now, we've got our basic function
shapes, we are ready to move on to

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00:04:30,060 --> 00:04:35,110
the next level of functional programming
in Java, the super powerful streams API.

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00:04:35,110 --> 00:04:36,380
Let's go plug in those shapes.