Build Your First Android App in Java

In this codelab, you’ll learn how to build and run your first Android app in the Java programming language. (If you’re looking for the Kotlin version of this codelab, you can go here.)

What you must know already

This codelab is written for programmers and assumes that you know Java programming language. If you are an experienced programmer and adept at reading code, you will likely be able to follow this codelab, even if you don’t have much experience with Java.

What you’ll learn

• How to use Android Studio to build your app.
• How to run your app on a device or in the emulator.
• How to add interactive buttons.
• How to display a second screen when a button is pressed.

Use Android Studio and Java to write Android apps

You write Android apps in the Java programming language using an IDE called Android Studio. Based on JetBrains’ IntelliJ IDEA software, Android Studio is an IDE designed specifically for Android development.

To work through this codelab, you will need a computer that can run Android Studio 3.6 or higher (or already has Android Studio 3.6 or higher installed).

Install Android Studio

Android Studio provides a complete IDE, including an advanced code editor and app templates. It also contains tools for development, debugging, testing, and performance that make it faster and easier to develop apps. You can use Android Studio to test your apps with a large range of preconfigured emulators, or on your own mobile device. You can also build production apps and publish apps on the Google Play store.

Android Studio is available for computers running Windows or Linux, and for Macs running macOS. The OpenJDK (Java Development Kit) is bundled with Android Studio.

The installation is similar for all platforms. Any differences are noted below.

1. Navigate to the Android Studio download page and follow the instructions to download and install Android Studio.
2. Accept the default configurations for all steps, and ensure that all components are selected for installation.
3. After the install is complete, the setup wizard downloads and installs additional components, including the Android SDK. Be patient, because this process might take some time, depending on your internet speed.
4. When the installation completes, Android Studio starts, and you are ready to create your first project.

. Task: Create your first project

In this step, you will create a new Android project for your first app. This simple app displays the string “Hello World” on the screen of an Android virtual or physical device.

Here’s what the finished app will look like:

What you’ll learn

• How to create a project in Android Studio.
• How to create an emulated Android device.
• How to run your app on the emulator.
• How to run your app on your own physical device, if you have one.

Step 1: Create a new project

1. Open Android Studio.
2. In the Welcome to Android Studio dialog, click Start a new Android Studio project.
3. Select Basic Activity (not the default). Click Next.
4. Give your application a name such as My First App.
5. Make sure the Language is set to Java.
6. Leave the defaults for the other fields.
7. Click Finish.

After these steps, Android Studio:

• Creates a folder for your Android Studio project called MyFirstApp. This is usually in a folder called AndroidStudioProjects below your home directory.
• Builds your project (this may take a few moments). Android Studio uses Gradle as its build system. You can follow the build progress at the bottom of the Android Studio window.
• Opens the code editor showing your project.

Step 2: Get your screen set up

When your project first opens in Android Studio, there may be a lot of windows and panes open. To make it easier to get to know Android Studio, here are some suggestions on how to customize the layout.

1. If there’s a Gradle window open on the right side, click on the minimize button (—) in the upper right corner to hide it.
2. Depending on the size of your screen, consider resizing the pane on the left showing the project folders to take up less space.

At this point, your screen should look a bit less cluttered, similar to the screenshot shown below.

Step 3: Explore the project structure and layout

The upper left of the Android Studio window should look similar to the following diagram:

Based on you selecting the Basic Activity template for your project, Android Studio has set up a number of files for you. You can look at the hierarchy of the files for your app in multiple ways, one is in Project view. Project view shows your files and folders structured in a way that is convenient for working with an Android project. (This does not always match the file hierarchy! To see the file hierarchy, choose the Project files view by clicking (3).)

1. Double-click the app (1) folder to expand the hierarchy of app files. (See (1) in the screenshot.)
2. If you click Project (2), you can hide or show the Project view. You might need to select View > Tool Windows to see this option.
3. The current Project view selection (3) is Project > Android.

In the Project > Android view you see three or four top-level folders below your app folder: manifests, java, java (generated) and res. You may not see java (generated) right away.

1. Expand the manifests folder.

This folder contains AndroidManifest.xml. This file describes all the components of your Android app and is read by the Android runtime system when your app is executed. 2. Expand the java folder. All your Java language files are organized here. The java folder contains three subfolders:

com.example.myfirstapp: This folder contains the Java source code files for your app.

com.example.myfirstapp (androidTest): This folder is where you would put your instrumented tests, which are tests that run on an Android device. It starts out with a skeleton test file.

com.example.myfirstapp (test): This folder is where you would put your unit tests. Unit tests don’t need an Android device to run. It starts out with a skeleton unit test file. 3. Expand the res folder. This folder contains all the resources for your app, including images, layout files, strings, icons, and styling. It includes these subfolders:

drawable: All your app’s images will be stored in this folder.

layout: This folder contains the UI layout files for your activities. Currently, your app has one activity that has a layout file called activity_main.xml. It also contains content_main.xml, fragment_first.xml, and fragment_second.xml.

menu: This folder contains XML files describing any menus in your app.

mipmap: This folder contains the launcher icons for your app.

navigation: This folder contains the navigation graph, which tells Android Studio how to navigate between different parts of your application.

values: This folder contains resources, such as strings and colors, used in your app.

Step 4: Create a virtual device (emulator)

In this task, you will use the Android Virtual Device (AVD) manager to create a virtual device (or emulator) that simulates the configuration for a particular type of Android device.

The first step is to create a configuration that describes the virtual device.

1. In Android Studio, select Tools > AVD Manager, or click the AVD Manager icon in the toolbar.
2. Click +Create Virtual Device. (If you have created a virtual device before, the window shows all of your existing devices and the +Create Virtual Device button is at the bottom.) The Select Hardware window shows a list of pre-configured hardware device definitions.
3. Choose a device definition, such as Pixel 2, and click Next. (For this codelab, it really doesn’t matter which device definition you pick).
4. In the System Image dialog, from the Recommended tab, choose the latest release. (This does matter.)
5. If a Download link is visible next to a latest release, it is not installed yet, and you need to download it first. If necessary, click the link to start the download, and click Next when it’s done. This may take a while depending on your connection speed.

6. In the next dialog box, accept the defaults, and click Finish.

The AVD Manager now shows the virtual device you added.

7. If the Your Virtual Devices AVD Manager window is still open, go ahead and close it.

Step 5: Run your app on your new emulator

1. In Android Studio, select Run > Run ‘app’ or click the Run icon in the toolbar. The icon will change when your app is already running.

2. In Run > Select Device, under Available devices, select the virtual device that you just configured. This menu also appears in the toolbar.

The emulator starts and boots just like a physical device. Depending on the speed of your computer, this may take a while. You can look in the small horizontal status bar at the very bottom of Android Studio for messages to see the progress.

Once your app builds and the emulator is ready, Android Studio uploads the app to the emulator and runs it. You should see your app as shown in the following screenshot.

Run your app on a device (if you have one)

What you need:

• An Android device such as a phone or tablet.
• A data cable to connect your Android device to your computer via the USB port.
• If you are using a Linux or Windows OS, you may need to perform additional steps to run your app on a hardware device. Check the Run Apps on a Hardware Device documentation. On Windows, you may need to install the appropriate USB driver for your device. See OEM USB Drivers.

Run your app on a device

To let Android Studio communicate with your device, you must turn on USB Debugging on your Android device.

On Android 4.2 and higher, the Developer options screen is hidden by default. To show Developer options and enable USB Debugging:

1. On your device, open Settings > About phone and tap Build number seven times.
2. Return to the previous screen (Settings). Developer options appears at the bottom of the list. Tap Developer options.
3. Enable USB Debugging.

Now you can connect your device and run the app from Android Studio.

1. Connect your device to your development machine with a USB cable. On the device, you might need to agree to allow USB debugging from your development device.
2. In Android Studio, click Run in the toolbar at the top of the window. (You might need to select View > Toolbar to see this option.) The Select Deployment Target dialog opens with the list of available emulators and connected devices.
3. Select your device, and click OK. Android Studio installs the app on your device and runs it.

Troubleshooting

If you’re stuck, quit Android Studio and restart it.

If Android Studio does not recognize your device, try the following:

1. Disconnect your device from your development machine and reconnect it.
2. Restart Android Studio.

If your computer still does not find the device or declares it “unauthorized”:

1. Disconnect the device.
2. On the device, open Settings->Developer Options.
3. Tap Revoke USB Debugging authorizations.
4. Reconnect the device to your computer.
5. When prompted, grant authorizations.

If you are still having trouble, check that you installed the appropriate USB driver for your device. See the Using Hardware Devices documentation.

Check the troubleshooting section in the Android Studio documentation.

Explore the app template

When you created the project and selected Basic Activity, Android Studio set up a number of files, folders, and also user interface elements for you, so you can start out with a working app and major components in place. This makes it easier to build your application.

Looking at your app on the emulator or your device, in addition to the Next button, notice the floating action button with an email icon.  If you tap that button, you’ll see it has been set up to briefly show a message at the bottom of the screen. This message space is called a snackbar, and it’s one of several ways to notify users of your app with brief information.

At the top right of the screen, there’s a menu with 3 vertical dots. If you tap on that, you’ll see that Android Studio has also created an options menu with a Settings item. Choosing Settings doesn’t do anything yet, but having it set up for you makes it easier to add user-configurable settings to your app.