Arrays and ArrayBuffers

An array is a data structure which stores a collection of elements and 0:00 has a fixed sized. 0:04 An array buffer on the other hand, gives us the same features as an array but 0:05 provides flexibility in terms of size. 0:09 The array buffer can grow and shrink as we need. 0:13 Let’s dive into the code and get comfortable with both. 0:16 Lets fire up IntelliJ and create a new package within our Source directory. 0:20 Right-click on Source, select New > Package. 0:25 Provide a package name, in our case collections. 0:29 And then we'll copy our SuperHeroes object. 0:32 And paste it into our collections package, click OK. 0:39 And within our SuperHeroes object we can get rid of everything but 0:42 our main function. 0:46 We will use this object as our main class to run all of our operations. 0:53 But in order to do so we will also need to edit our configurations. 0:57 So we'll click Edit Configurations, and for our main class, 1:01 we'll select the SuperHeroes in the collections package. 1:05 Click OK, and then Apply, and OK. 1:10 There are a few different ways to create an array. 1:13 Let's dive into how arrays work by implementing them. 1:16 Great, we create the array by supplying the new keyword, followed by array, 1:27 the type, and also the array size. 1:32 Here we've created an array of integers called numbers with length 10, 1:34 all initialized to the integer 0. 1:38 Similarly, we can create an array of all strings 1:41 Again, we supply the new keyword, the array keyword, 1:52 the type information, and the array size. 1:56 Often times we may want to create an array with some initial values. 1:59 In that instance we don't need to provide the new key word. 2:03 Let's take a look. 2:06 You may have noticed that we don't have to specify the type that's because 2:21 Scala's type inference can in further type from the values we passed to the array. 2:25 A big different from Java and many other languages, 2:30 which you may have used to access values at a specific index of the array, 2:33 we use parenthesis instead of square brackets. 2:38 Arrays are 0 index and we can access the fourth element by using the parenthesis. 2:45 In this case this should print out Batman. 2:50 Let's compile and run our application, awesome. 2:53 One issue that we will encounter is adding or removing elements from our heros array. 2:58 Let's say we wanted to add Iron Man to our list of heroes. 3:03 We can use the colon plus method on our arrays. 3:06 However, this would create an entirely new array. 3:10 Array buffers to the rescue. 3:13 To create an array buffer we need to import the scala.collection.muteable 3:15 package or specifically the array buffer class within the package. 3:19 Let's do so at the top of our file and create a new array buffer. 3:24 [SOUND] 3:34 Awesome. 3:57 To add a new element to the ArrayBuffer, we would use the += method. 3:57 Additionally, we can add multiple elements by enclosing them in parentheses 4:07 Similarly, we can add an entire collection by using the plus plus equals method. 4:11 Let's create an array to append to our mutable heroes. 4:17 Awesome, here append other heroes to our mutable heroes. 4:44 Arrays and array buffers have a ton built in functions you should get familiar with. 4:48 I've included links in the teacher notes to the actual documentation. 4:52 Remember our array buffer is mutable. 4:56 So let's run a few operations on our heros to get more familiar. 4:59 Let's print out the contents of our array buffers so 5:04 we have an idea of what it's currently storing. 5:06 Awesome. We see that we have an array buffer 5:15 with all the values that we've added to it. 5:17 Additionally we can remove a number of elements starting from the right 5:19 of the array buffer. 5:23 TrimEnd allows us to remove a number of elements starting from the end of 5:30 the array buffer. 5:34 In this case we make use of the update method which lets us update the value at 5:45 a specific index. 5:50 Therefore replacing Thor with Flash. 5:51 Let's reprint the contents of our mutableHeroes array and 5:55 see how things have changed. 5:58 Rerun our application. 6:03 And the first thing we notice is that Thor has been replaced with Flash. 6:05 Additionally, we notice that Starfire, as well as Green Arrow, have been removed 6:10 from our array buffer Awesome we learned how to create arrays and array buffers. 6:15 Now let's traverse through our mutable heroes array buffer. 6:20 As we previously covered we can use the four loops in Scala 6:24 to loop through an array or an array buffer. 6:27 We'll comment out our previous print line statements. 6:41 Here, we follow the left arrow operator, 6:47 which loops through each element in the array buffer. 6:49 Let's recompile and rerun our app. 6:52 Great, now we've printed out every element in our mutable 6:57 heros array buffer to the screen. 7:00 If you recall from an earlier lesson, Scalas supports inclusive and 7:03 exclusive ranges. 7:07 For an exclusive range, we use the keyword until. 7:08 Let's recompile and run our app. 7:19 Awesome. 7:24 We notice that our result, 10, is not included. 7:24 For an inclusive range, we have to use the keyword to 7:28 Let's recompile and run our app. 7:39 Great and in this case we see that 10 is included. 7:44 However there may be certain instances where we'd also like the index values. 7:47 In this case we print out the index and the value of the specified index. 8:12 Until provides us with an exclusive range, so 8:17 there's no need to subtract one from the array buffer length. 8:20 Awesome, as expected we get the index value along with the element 8:23 at that index. 8:27 With an inclusive to, 8:28 we will need to subtract one from our mutableHeroes length. 8:30 Otherwise, we would get an index out of bounds error. 8:33 In earlier videos we learned about four comprehension and guards. 8:56 These concepts are very useful when transforming arrays. 9:00 Let's create a new array with any heros whose name contains a dash. 9:04 The yield keyword will create the same type of collection as the one we start 9:24 with and the guard will provide filters on our data to any element in the array 9:29 that contains a dash. 9:33 Let's see how that works by printing out the element 9:35 in the dash heroes array buffer. 9:38 As expected, our dash here as array buffer only contains one element, 9:44 Spider-man, as it's the only element that has a dash in its name. 9:48 Great, we learned how to create, traverse, and update arrays and array buffers In 9:53 the next video we'll focus on another set of data structures called list and 9:57 list buffers. 10:02 See you there. 10:02