WEBVTT 1 00:00:00.025 --> 00:00:07.730 [SOUND] Hello, I’m Craig and I’m a developer. 2 00:00:07.730 --> 00:00:12.116 In this workshop, we’ll take a look at a relatively new language construct for 3 00:00:12.116 --> 00:00:13.105 Java, lambdas. 4 00:00:13.105 --> 00:00:15.497 Now in general, lambdas are not a new concept and 5 00:00:15.497 --> 00:00:18.424 they’re available in many other programming languages. 6 00:00:18.424 --> 00:00:22.170 You may have heard them referred to as anonymous functions. 7 00:00:22.170 --> 00:00:25.440 They provide the building blocks to a more declarative style of coding 8 00:00:25.440 --> 00:00:26.620 known as functional programming. 9 00:00:27.900 --> 00:00:30.270 Java 8, which was released in March of 2014, 10 00:00:30.270 --> 00:00:33.670 introduced several new changes to the Java syntax. 11 00:00:33.670 --> 00:00:38.040 The introduction of lambdas on the surface is basically just syntactic sugar or 12 00:00:38.040 --> 00:00:40.550 a better way to say, the same thing in code. 13 00:00:40.550 --> 00:00:45.392 Its sugar is replacing what was already available to us through creating inline 14 00:00:45.392 --> 00:00:49.222 anonymous classes, but aside from being much more legible and 15 00:00:49.222 --> 00:00:52.559 concise the introduction means more to the language. 16 00:00:52.559 --> 00:00:56.635 It promotes the concept of functions as a first class citizen and 17 00:00:56.635 --> 00:00:59.966 enters Java into the functional programming arena. 18 00:00:59.966 --> 00:01:03.654 In this workshop, we'll reacquaint ourselves with the old way of doing 19 00:01:03.654 --> 00:01:08.680 things and then explore the shiny new more succinct declarative function way. 20 00:01:08.680 --> 00:01:12.164 Lambdas may look a little strange when you run across them for the first time, so 21 00:01:12.164 --> 00:01:15.442 I wanted to make sure that you were able to read them when you bump into them. 22 00:01:15.442 --> 00:01:18.244 Now more and more, as code bases upgrade to Java 8, 23 00:01:18.244 --> 00:01:22.530 lambda expressions are quickly becoming the de facto way to accomplish tasks. 24 00:01:23.730 --> 00:01:24.810 Let's go get cozy with lambdas. 25 00:01:26.420 --> 00:01:28.240 So first, let's get refreshed. 26 00:01:28.240 --> 00:01:29.230 Now I've gone ahead and 27 00:01:29.230 --> 00:01:33.390 I built an IntelliJ project that you can download, it's in the teacher's notes. 28 00:01:33.390 --> 00:01:36.925 So let's open it up and take a peek, then we click open. 29 00:01:36.925 --> 00:01:39.578 And in the download folder here, I unzip this lambda and 30 00:01:39.578 --> 00:01:41.962 there's this thing here that's called Lambda. 31 00:01:41.962 --> 00:01:44.850 So, I'm gonna click Choose on that and it's gonna open things up. 32 00:01:46.010 --> 00:01:50.280 A common question that I get on the forum is asking what Java books I recommend? 33 00:01:50.280 --> 00:01:52.566 So, I thought we'd kill two birds with one stone. 34 00:01:52.566 --> 00:01:55.728 This tiny little project here is gonna print out some Java books that I've 35 00:01:55.728 --> 00:01:57.000 been reading. 36 00:01:57.000 --> 00:02:00.380 So first things first, I've created the book class for us already, 37 00:02:00.380 --> 00:02:01.400 you can get to it over here. 38 00:02:02.540 --> 00:02:05.050 It's a pretty basic class and it could definitely be improved on, but 39 00:02:05.050 --> 00:02:06.419 it'll give us what we need right now. 40 00:02:06.419 --> 00:02:09.341 So the way that you do it is when you create a book to the constructor, 41 00:02:09.341 --> 00:02:12.340 you pass the title, the author and a publication date of an integer. 42 00:02:12.340 --> 00:02:16.149 So like the year date there and then I also made a little toString method here, 43 00:02:16.149 --> 00:02:17.896 so we could kinda take a look at that. 44 00:02:17.896 --> 00:02:22.452 And then I have another class here called Books and books has a static method on it 45 00:02:22.452 --> 00:02:25.420 that returns a list of books and it's called all. 46 00:02:25.420 --> 00:02:29.783 Now static methods are nice, because they don't require us to create an instance. 47 00:02:29.783 --> 00:02:32.990 We can just kind of access that method right off the class. 48 00:02:32.990 --> 00:02:37.898 So basically, what this is doing is giving us a list of book objects to play with. 49 00:02:37.898 --> 00:02:40.870 We're gonna use them to loop and sort through some things. 50 00:02:40.870 --> 00:02:45.401 So let's review the anonymous inline class version of how we solve this 51 00:02:45.401 --> 00:02:46.994 problem before Java 8. 52 00:02:46.994 --> 00:02:49.494 How did we sort things before Java 8? 53 00:02:49.494 --> 00:02:54.290 So we explored the style just previously in the Java data structures course. 54 00:02:54.290 --> 00:02:58.690 So let's come over here in main and let's make a new static method here. 55 00:02:58.690 --> 00:03:05.199 It's not gonna return anything, we're just gonna print out to the screen and 56 00:03:05.199 --> 00:03:09.560 we're gonna call it usingAnonymousInlineClass. 57 00:03:09.560 --> 00:03:13.461 So first things first, let's get a list of our books and 58 00:03:13.461 --> 00:03:15.869 we're gonna use the Books.all. 59 00:03:15.869 --> 00:03:17.280 Now it's saying, it doesn't know what list. 60 00:03:17.280 --> 00:03:20.399 See how it's red there and it's suggesting that we import it and it says, 61 00:03:20.399 --> 00:03:21.161 do you mean this? 62 00:03:21.161 --> 00:03:23.260 So, I'm gonna press what it suggests there. 63 00:03:23.260 --> 00:03:26.243 It says, option and then Enter and choose Java.util.List. 64 00:03:26.243 --> 00:03:28.371 There we go and I don't have the name of it, so 65 00:03:28.371 --> 00:03:31.170 we're gonna call it books as the name. 66 00:03:31.170 --> 00:03:34.460 There's a static method off of the collections object called sort. 67 00:03:36.440 --> 00:03:39.334 Let's go ahead and take care of the collections that we were talking about. 68 00:03:39.334 --> 00:03:44.107 And it takes two parameters, it takes books and 69 00:03:44.107 --> 00:03:47.687 then it takes a comparator class and 70 00:03:47.687 --> 00:03:54.400 a comparator is an interface and it's a generic interface. 71 00:03:54.400 --> 00:03:57.181 Let's go ahead and import that too. 72 00:03:57.181 --> 00:04:02.040 And you'll see that this is telling me that I've got something wrong with it. 73 00:04:02.040 --> 00:04:03.725 So let's mouse over here and see what it says. 74 00:04:03.725 --> 00:04:08.159 It says, the anonymous derived from comparator must either be declared 75 00:04:08.159 --> 00:04:12.900 abstract or implement the abstract method compare of type to type. 76 00:04:12.900 --> 00:04:14.454 This is exactly what we had done before, 77 00:04:14.454 --> 00:04:16.476 I just wanted to show you this over here in IntelliJ. 78 00:04:16.476 --> 00:04:19.844 Let's go ahead and let this, we'll say, implement methods. 79 00:04:19.844 --> 00:04:21.461 So we'll write out the method that we did. 80 00:04:21.461 --> 00:04:22.698 Now before we did this by hand, but 81 00:04:22.698 --> 00:04:25.400 we're gonna do this compare method here is the one that it actually needs. 82 00:04:27.080 --> 00:04:32.390 Now we're making a brand new anonymous class from this interface and 83 00:04:32.390 --> 00:04:36.650 we're overwriting the one abstract method that needed to be completed and 84 00:04:36.650 --> 00:04:38.650 that's this compare method. 85 00:04:38.650 --> 00:04:41.941 And let's name these things o1 o2. 86 00:04:41.941 --> 00:04:44.990 Let's call it b2, so we know that they're books. 87 00:04:44.990 --> 00:04:53.861 And so we're gonna return the title and we're gonna compare it to, 88 00:04:53.861 --> 00:04:58.423 cuz remember, these comparators were is that returns negative 89 00:04:58.423 --> 00:05:01.779 one if it's less, zero if it's equal, one one if it isn't. 90 00:05:01.779 --> 00:05:05.780 And strings have a method on them called compareTo. 91 00:05:05.780 --> 00:05:08.359 And since we're gonna just sort by the title of the book, 92 00:05:08.359 --> 00:05:11.046 what we're gonna do is here is we're gonna get the title and 93 00:05:11.046 --> 00:05:14.465 we're gonna use the compareTo on string to compare it to the other string. 94 00:05:14.465 --> 00:05:19.580 So that's how the sorting works through the process here. 95 00:05:19.580 --> 00:05:21.698 So now we've pushed the books in here. 96 00:05:21.698 --> 00:05:24.622 The books should now be sorted, so let's go ahead and let's just print out and 97 00:05:24.622 --> 00:05:26.010 make sure that the books are sorted. 98 00:05:29.303 --> 00:05:33.064 We’ll look through all the books for each book in books and 99 00:05:33.064 --> 00:05:34.845 we’ll print out the book. 100 00:05:34.845 --> 00:05:36.832 Cool. 101 00:05:36.832 --> 00:05:38.828 Let’s go ahead and call our new function here. 102 00:05:38.828 --> 00:05:43.465 We’ll say, usingAnonymousInLineClass and now I’m gonna run that. 103 00:05:46.490 --> 00:05:48.468 Awesome. So here it is and they are sorted and 104 00:05:48.468 --> 00:05:52.230 you'll remember from before, this books, they're not sorted here. 105 00:05:52.230 --> 00:05:55.206 But because we ran it through that sort function here, they are clean code, 106 00:05:55.206 --> 00:05:56.657 effective Java, functional Java. 107 00:05:56.657 --> 00:05:59.665 Prior to Java 8, this is how you did things. 108 00:05:59.665 --> 00:06:03.924 Now let's take a look at that again, this is how you did things. 109 00:06:03.924 --> 00:06:05.590 It’s pretty ugly. 110 00:06:05.590 --> 00:06:10.535 I mean, that’s a lot of lines of code just to get this one liner here out. 111 00:06:10.535 --> 00:06:14.464 Now the main reason for all this code is because until very recently, 112 00:06:14.464 --> 00:06:18.160 there was no way to have a method outside of a class. 113 00:06:18.160 --> 00:06:22.643 So developers dealt with this hindrance by creating an interface, like this one here. 114 00:06:22.643 --> 00:06:26.553 This comparator, this is an interface or an abstract class and 115 00:06:26.553 --> 00:06:28.420 it just had a single method. 116 00:06:28.420 --> 00:06:29.097 Like this one here. 117 00:06:29.097 --> 00:06:31.660 Compare that was required to be implemented. 118 00:06:32.920 --> 00:06:34.770 Now this pattern became so 119 00:06:34.770 --> 00:06:39.995 heavily used that it is known as a single abstract method or SAM for short. 120 00:06:39.995 --> 00:06:41.240 S-A-M. 121 00:06:41.240 --> 00:06:44.144 Now while the acronym is short, its implementation is not. 122 00:06:44.144 --> 00:06:46.830 It kinda reminds me of that George Carlin joke, 123 00:06:46.830 --> 00:06:49.122 how come abbreviate is such a long word? 124 00:06:49.122 --> 00:06:52.448 A lot of event-driven code use SAMs to handle the event 125 00:06:52.448 --> 00:06:55.040 without creating a separate class. 126 00:06:55.040 --> 00:06:57.728 So you'll see this solution all over the place and 127 00:06:57.728 --> 00:07:01.256 it's definitely one of the reasons that Java gets a lot of flack. 128 00:07:01.256 --> 00:07:05.883 So Java developers asked for a quicker and more succinct way to add dynamic code, and 129 00:07:05.883 --> 00:07:09.532 the Java community process members listened to the complaints and 130 00:07:09.532 --> 00:07:10.652 they made a change. 131 00:07:10.652 --> 00:07:14.640 If you're interested in how this process works, please check the teacher's notes. 132 00:07:14.640 --> 00:07:20.580 So, a method outside of a class is called a function and they're now part of Java. 133 00:07:20.580 --> 00:07:25.090 When you have an unnamed, anonymous function, it's called a lamba. 134 00:07:25.090 --> 00:07:27.826 Lambas can be used anywhere that SAMs were used before. 135 00:07:27.826 --> 00:07:31.480 In fact, they're now called functional interfaces. 136 00:07:31.480 --> 00:07:33.460 Let's write one up, right after this quick break.