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Google have made Kotlin a top-level

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language for Android development, which

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means that it's fully supported in

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Android Studio. And they'll also be

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publishing example code using Kotlin, as

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well as Java. At the moment though, most

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of their code samples are still in Java.

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Now, it turns out that's not a huge problem,

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because we're gonna look, in this section,

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at how Android Studio can convert Java

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code to Kotlin for us. So in this section,

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we're going to look at the Kotlin

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programming language, just to give you an

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overview and introduction to it. So let's

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get started. Now Android Studio's

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designed for Android development, which

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means that the projects it creates are

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intended to be run on an Android device,

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and not on your computer. Now it is

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possible, though, to get Android Studio to

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compile and run pure Kotlin code. It is

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very fiddly, so we've created a project

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for you. Now this that Android Studio

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project's been specifically configured, to

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run pure Kotlin code that'll run on

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your computer. Now before I show you how

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to get that working, there's another

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alternative. Now if you're already using

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IntelliJ as your IDE, then I recommend

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using that for these tutorials instead.

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Now Android Studio is based on IntelliJ

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IDEA, so everything will work, just as is,

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in the videos. Now you may also be taking

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Sarah Etrich's Kotlin for Java

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Developers' course, in which case you'll

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see how to install IntelliJ IDEA in that

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course. For everybody else, though, I'm going

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to go through the steps to get Android

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Studio to run pure Kotlin code. Now the

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project we've created is in a zip file

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in the resources section of this video.

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So let's just move over now, and I'm

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going to show you how to get that zip

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file how to unzip it, and get it ready

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for use on your computer.

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Alright, so the project we've created

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is in a zip file in the resources

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section of this video, and this is the

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file that we're going to be using for

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our Kotlin tutorial. And if you move the

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mouse over the video,

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a pop up balloon will appear at the top

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left, and just above that you'll see a

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menu icon. And if you click on that and

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scroll down to this video in the list,

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you'll actually see an area where you

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can download the file - and the file that

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you want is called KotlinTutorial.zip.

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So you can check that out and

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download that file because we'll need

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that file to actually work on these

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tutorials - the Kotlin tutorial. And if

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you've got any problems finding the

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Kotlin tutorial file, just look in this

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lecture - the lecture that you're

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looking at now. Basically, just go into

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the top left of the screen and you

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should see a resources section, but also,

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the last lecture of the course has got a

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list of all the downloads, so you can

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grab it from there as well. And what you

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need to do is download that file -

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KotlinTutorial.zip - and put it

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somewhere on your computer. And you can

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see, in my case, I'm on a Mac and I've

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downloaded into a folder. Once you've

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done that you need to unzip it. Now in my

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case, on a Mac, I can just double-click

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the file to unzip it, and you can see it

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creates a sub-folder. Now if you're on a

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Windows machine or a Linux machine, you'll

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most likely have to right-click that

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file and select Expand all or Uncompress

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or words to that effect, and expand that

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directory out. And make a note of where

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that directory is, because we'll need

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that when we go back to Android Studio.

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Alright, so let's go back to Android

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studio now. Alright, so now that we've

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downloaded and unzipped the Kotlin

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tutorial files, next step is to open it

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in Android Studio. So click on Open an

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existing Android Studio project. You want

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to navigate to the folder where the file

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has been unzipped. In my case, it's Kotlin

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tutorial so I'm going to double click on

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that to open it, and click on Open. Now

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Android Studio will load the project and

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it may take quite a while the first time,

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while it builds the project. On Windows

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in particular, be prepared to wait about

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a minute before the project fully loads.

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And while it's loading, you may get an

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error like this, or a warning like this,

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basically saying that the path, and

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whatever the path is that we've

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actually used to create the zip file,

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doesn't belong to a directory. Just click

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OK to that, and Android Studio's then

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going to use the setup or configuration

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that you've done in your version of

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Android Studio.

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Alright, so we've now got the project open

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in Android Studio. Now you may actually

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be asked if you want to upgrade the

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version of the Kotlin plugin or gradle,

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used by this project. So if you do get

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asked that, don't do it. Now we normally

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suggest that you accept all the updates

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Android Studio offers, but don't update

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anything in this particular project. The

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reason is that we spent a lot of time

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hacking the gradle files around to make

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this work. Updating Google or the Kotlin

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plugin will break those changes. Now if

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that happens, the program won't compile.

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You'll need to delete the project

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directory and extract it from the zip

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file again. Alright, so we've now

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got the project open in Android Studio.

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Now the main part of the window is the

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edit window, which is currently empty -

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that's this part here. And it shows some

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useful shortcuts but there's no

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file displayed, because we're not editing

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anything yet. And over to the left here is

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the project panel, or project pane, and this

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shows the files making up our project

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and at the moment, we're only interested

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in what Main.kt is over here. So

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just before we go into it, I'm going

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to explain briefly what are these other

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things. So the Gradle Scripts folder - that

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heading there contains various

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configuration options for the gradle

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build system, so I can open that up and

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have a look there. Now gradle's

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responsible for things like compiling

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our Kotlin code, and producing the

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executable that we can run. It's gradle

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that we had to change to get Android

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Studio to cope with plain Kotlin, rather

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than the Android project structure that it

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was designed for. Now we're going to be

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looking at a couple of the files in

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there later, but for now you can safely

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ignore everything in this section. Now

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the top of the project pane is our

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project, KotlinTutorial, which you can see

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highlighted. And expand that if you

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haven't already, and again, it should be -

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it shows a Java sub-folder here, as you

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can see. Now I know this was a Kotlin

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course, but historically, everything was

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written in Java. So consequently,

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Android Studio wants that directory to be

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called Java. Now below that is the Kotlin

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source code file. We're going to be

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creating more of these, but at the moment,

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there's only the one Kotlin file in the

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project. And by the way, it's possible to

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mix Java and Kotlin source code in the

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same project. Now if you do that,

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the Java files will have a dot Java

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extension, and the Kotlin files will have

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a dot kt extension, as you can see in

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this example here. Now to edit a file, you

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just need to double-click it. So we can

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open main by double-clicking it now,

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which I'm going to do - Main.kt - and that

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shows some Lotlin code on the screen

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there. Now this is a very simple Kotlin

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program, and I'm going to be going

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through what it all means, shortly. For

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now though, we have to get it working. Now

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let's try running the program. Now it

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turns out there's four different ways to

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do that and they all do the same thing.

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Now we could go to the run menu, up here,

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and click on and select run kt,

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Run Mainkt. We can also right-click

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on the editor here, and choose Run Main

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kt there, from the context menu.

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Now by the way, sometimes the menu

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doesn't appear there, but it does when

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you right-click on Main.kt in the

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project pane. So you might need to click on

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that - right-click - and Run

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Mainkt there, to get it to show. The

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fourth way to run is to use this green

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triangle in the toolbar. Now what that

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does can vary and the drop-down list on

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its left will tell you what it's going

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to run. So you can see over here, it's

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telling you it's gonna be running Main

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kt. So in other words, it's set to Main

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kt so it's going to run our main, or

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our current, Kotlin file. But watch out

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for that, because we're gonna be using

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different files as we work through these

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videos. So keep an eye on what it says

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over here in that Dropbox, to make sure

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that you're running the correct file.

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Alright, so we've got four different ways

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to run this program but none of them

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will work. As I said, we had to hack

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around with the project files to get

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this to work with Android Studio, but

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there's one final step we couldn't get

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past. So use any one of these four

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methods and run the program. In my case,

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I'm going to right-click for the Main.

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kt, over here in the project pane, and

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choose Run Mainlt from there.

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Now the project will be built, as it

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was there, but you'll actually get an

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error, and you can see this error: Could

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not find or load main class Main

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kt. Now this will only happen the

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first time we try this, so just follow

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along and run the program and you'll get

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the error like I've got here now. Once

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that's happened, and you see the error, as

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you can see in the screen there: Could

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not find or load class Mainkt, go to

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the Build menu up here, and click on

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Rebuild Project. Then when you do that,

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nothing really seems to happen, but now

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the project will run using any of the

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four methods. Now it's a tradition that

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the first program you write in a new

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language should print Hello World, and

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that's what this program does. So let's

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try running it - I'm don't go do it the same

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way, try running it the same way - select

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Run Mainkt. And you can see, in this

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case, now that we've done that, we're

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successfully getting the text to output

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on the screen; Hello World. Alright, so

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that's our project set up and working.

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Now we're going to use this same

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project throughout these tutorial videos,

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and add new files as we go along. As you

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start each new video, make sure you've

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got this project open in Android Studio.

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And again, as a recap, the reason we've

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done all this, is because it's much

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easier to explain Kotlin when we can

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just run our programs directly, rather

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than having to run them as an Android

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app in an emulator. Now there are two

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ways to close the project; if you just

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close Android Studio using the close

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icon at top left, up here, or top

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right on Windows, then the project will

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open again automatically, the next time

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you start Android Studio. Personally, I

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prefer to go to the File menu, and

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choose Close Project first. Now when

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you do that, Android Studio starts up on

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the welcome screen, as you can see here.

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But it also remembers the last projects

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you've opened, so you can come over here and

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click on Kotlin tutorial in the list, to

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open the project again.

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Alright, so we're all set up now. So I'm

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going to stop the video here, and in the

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next video, we'll start looking at the

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Kotlin language and what we can do with

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it. See you in the next video.