Bummer! This is just a preview. You need to be signed in with a Basic account to view the entire video.
Function Shapes - Function and Predicate4:36 with Craig Dennis
Let's review the remaining basic function shapes, Function and Predicate.
Okay, so we've got to look at consumer and supplier. 0:00 So next up in our list of important function shapes 0:04 is the root of all of these, function. 0:08 Now, it gets a little bit weird when we start looking at this. 0:11 So this represents a function that accepts a one argument and produces a result. 0:14 So we're gonna click into here a nd this is a function functional interface. 0:18 It gets a little weird talking about it. 0:24 Don't worry, I didn't pick up a stutter. 0:25 So, a function takes a single argument and produces a result. 0:27 And both the parameter type and the return value are specified, right? 0:33 That's what the T and the R are. 0:38 So T is the type that's passed in and R is the result type. 0:40 So let's swing down. 0:44 Let's take a look at the single abstract method and it's called apply. 0:46 So again, it accepts a T and it returns an R. 0:50 So, when you define the function, you specify what type it expects and 0:54 then the type of the return value. 0:59 So as you can imagine, these are great for 1:01 transforming values from one to another and going between types. 1:03 The both can be strings but you can switch between types. 1:08 We'll get our feet wet with these here in a bit when we explore streams. 1:12 Another thing that I wanted to point out here in the ducts, while we're here. 1:15 There are these things called default methods which are new to java eight 1:19 interfaces and they allow you to change several functions together. 1:24 So if we click here, if we click this default methods, we'll see that you can go 1:27 on every function that has this method that says and then and 1:31 you can pass in a function okay. 1:34 So you can kind of chain several of these functions together. 1:36 You call your function and then call another and then another and 1:40 it just sort of goes flowing between them. 1:43 This is called functional composition and as you guessed, I'm gonna go ahead and 1:45 park that right now. 1:50 Let's flip over and let's write that here. 1:51 We'll write functional composition. 1:54 We are getting a pretty healthy looking list for the parking lot there. 1:57 Can't wait to go over this stuff, but we'll get to it in a bit, don't worry. 2:01 So about these default methods, 2:06 check the teacher's notes if it needs some more information about that. 2:07 Other super powerful and 2:11 there's a couple of these interfaces that have some pretty handy default methods. 2:12 Okay and last but definitely not least, let's check out Predicate. 2:18 Predicate is our shape here, 2:25 and it represents a Predicate, thank you boolean-valued function of one argument. 2:27 So what happens here is if we look at this abstract method, it has an abstract 2:34 method of name test and it will take a type t and always return true or 2:39 false so it's really kind of a specific type of function right, of the function, 2:44 functional interface so it will take a type and return a true or false. 2:49 Pretty nice, right? 2:55 It's very specific. 2:55 So, just like functions, it has a default method and 2:57 you can kind of chain these together. 3:00 So you can say, this and this or not this, so you can negate it or do an or. 3:02 We'll get our hands wet with these real soon as we use these 3:08 often when trying to filter values. 3:12 The java.util function package has some wonderful functional interfaces 3:14 that we can lean on when diving deeper into functional programming. 3:19 I'm glad you got a chance to see how to explore the out of the box options. 3:22 Let's review the four basic shapes that I'd like you to be 3:26 familiar with real quick. 3:29 Consumer, a function that accepts something and returns nothing. 3:30 These are useful when you need to be provided a value in context. 3:35 Supplier, this accepts nothing but returns a value. 3:39 This is great when you need something initially, like we did in our yell method. 3:43 Function, this takes a single argument, and returns a value. 3:47 This is great for transformation. 3:51 And Predicate accepts a parameter, and 3:54 returns a boolean value, helpful when filtering value. 3:56 You probably noticed that the remaining functional interfaces in the package where 4:00 either a typed version of those four or 4:05 a version that changes the amount of parameters that the function accepts. 4:07 The amount of parameters that a function accepts is referred to as parity. 4:11 If it helps, I remember the bi prefix like the bicycle, like two wheels, 4:15 like this bike here, two wheels. 4:19 Now, that is versus the uni prefix like unicycle which means one wheel. 4:21 So now, we've got our basic function shapes, we are ready to move on to 4:26 the next level of functional programming in Java, the supper powerful streams API. 4:30 Let's go plug in those shapes. 4:35
You need to sign up for Treehouse in order to download course files.Sign up