1. What is Android?
Android is an operating system based on Linux with a Java programming interface.
The Android Software Development Kit (Android SDK) provides all necessary tools to develop Android applications. This includes a compiler, debugger and a device emulator, as well as its own virtual machine to run Android programs.
Android is currently primarily developed by Google.
Android allows background processing, provides a rich user interface library, supports 2-D and 3-D graphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database.
Android applications consist of different components and can re-use components of other applications. This leads to the concept of a task in Android; an application can re-use other Android components to archive a task.
For example you can write an application which use the Android Gallery application to pick a photo.
The Android Software Development Kit (Android SDK) provides all necessary tools to develop Android applications. This includes a compiler, debugger and a device emulator, as well as its own virtual machine to run Android programs.
Android is currently primarily developed by Google.
Android allows background processing, provides a rich user interface library, supports 2-D and 3-D graphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database.
Android applications consist of different components and can re-use components of other applications. This leads to the concept of a task in Android; an application can re-use other Android components to archive a task.
For example you can write an application which use the Android Gallery application to pick a photo.
Google offers the Google Play service in which programmers can offer their Android application to Android users. Google phones include the Google Play application which allows to install applications.
Google Play also offers an update service, e.g. if a programmer uploads a new version of his application to Google Play, this service will notify existing users that an update is available and allow to install it.
Google Play used to be called Android Market.
Google Play also offers an update service, e.g. if a programmer uploads a new version of his application to Google Play, this service will notify existing users that an update is available and allow to install it.
Google Play used to be called Android Market.
During deployment on an Android device, the Android system will create a unique user and group ID for every Android application. Each application file is private to this generated user, e.g. other applications cannot access these files.
In addition each Android application will be started in its own process.
Therefore by means of the underlying Linux operating system, every Android application is isolated from other running applications.
If data should be shared, the application must do this explicitly, e.g. via a Service or a ContentProvider.
Android also contains a permission system. Android predefines permissions for certain tasks but every application can define additional permissions.
An Android application declare its required permissions in its
Permissions have different levels. Some permissions are automatically granted by the Android system, some are automatically rejected.
In most cases the requested permissions will be presented to the user before installation of the application. The user needs to decide if these permissions are given to the application.
If the user denies a permission required by the application, this application cannot be installed. The check of the permission is only performed during installation, permissions cannot be denied or granted after the installation.
Not all users pay attention to the required permissions during installation. But some users do and they write negative reviews on Google Play.
In addition each Android application will be started in its own process.
Therefore by means of the underlying Linux operating system, every Android application is isolated from other running applications.
If data should be shared, the application must do this explicitly, e.g. via a Service or a ContentProvider.
Android also contains a permission system. Android predefines permissions for certain tasks but every application can define additional permissions.
An Android application declare its required permissions in its
AndroidManifest.xml configuration file.For example an application may declare that it requires InternetPermissions have different levels. Some permissions are automatically granted by the Android system, some are automatically rejected.
In most cases the requested permissions will be presented to the user before installation of the application. The user needs to decide if these permissions are given to the application.
If the user denies a permission required by the application, this application cannot be installed. The check of the permission is only performed during installation, permissions cannot be denied or granted after the installation.
Not all users pay attention to the required permissions during installation. But some users do and they write negative reviews on Google Play.
The following gives a short overview of the most important Android components.
An Activity represents the presentation layer of an Android application. A simplified description is that anActivity represents a screen in your Android application. This is slightly incorrect as Activities can be displayed as dialogs or can be transparent.
An Android application can have several Activities.
An Android application can have several Activities.
Views are user interface widgets, e.g. buttons or text fields. The base class for all Views is the
A ViewGroup is responsible for arranging other Views. ViewGroups is also called layout managers. The base class for these layout managers is the
android.view.View class. Views have attributes which can be used to configure their appearance and behavior.A ViewGroup is responsible for arranging other Views. ViewGroups is also called layout managers. The base class for these layout managers is the
android.view.ViewGroup class which extends the Viewclass.ViewGroups can be nestled to create complex layouts. You should not nestle ViewGroups too deeply as this has a negative impact on the performance.
Intents are asynchronous messages which allow the application to request functionality from other components of the Android system, e.g. from Services or Activities. An application can call a component directly (explicit Intent) or ask the Android system to evaluate registered components based on the Intentdata (implicit Intents ). For example the application could implement sharing of data via an
Intents allow to combine loosely coupled components to perform certain tasks.
Intent and all components which allow sharing of data would be available for the user to select. Applications register themselves to an Intent via an IntentFilter.Intents allow to combine loosely coupled components to perform certain tasks.
Services perform background tasks without providing a user interface. They can notify the user via the notification framework in Android.
A ContentProvider provides a structured interface to application data. Via a ContentProvider your application can share data with other applications. Android contains an SQLite database which is frequently used in conjunction with a ContentProvider. The SQLite database would store the data, which would be accessed via the ContentProvider.
BroadcastReceiver can be registered to receive system messages and Intents. A BroadcastReceiver will get notified by the Android system, if the specified situation happens. For example a BroadcastReceivercould get called once the Android system completed the boot process or if a phone call is received.
Widgets are interactive components which are primarily used on the Android homescreen. They typically display some kind of data and allow the user to perform actions via them. For example a Widget could display a short summary of new emails and if the user selects an email, it could start the email application with the selected email.
Android provide many more components but the list above describes the most important ones. Other Android components are Live Folders and Live Wallpapers . Live Folders display data on the homescreen without launching the corresponding application while Live Wallpapers allow to create annimated backgrounds.
The Android Software Development Kit (SDK) contains the necessary tools to create, compile and package Android application. Most of these tools are command line based.
The Android SDK also provides an Android device emulator, so that Android applications can be tested without a real Android phone. You can create Android virtual devices (AVD) via the Android SDK, which run in this emulator.
The Android SDK contains the Android debug bridge (adb) tool which allows to connect to an virtual or real Android device.
The Android SDK also provides an Android device emulator, so that Android applications can be tested without a real Android phone. You can create Android virtual devices (AVD) via the Android SDK, which run in this emulator.
The Android SDK contains the Android debug bridge (adb) tool which allows to connect to an virtual or real Android device.
Google provides the Android Development Tools (ADT) to develop Android applications with Eclipse. ADT is a set of components (plug-ins) which extend the Eclipse IDE with Android development capabilities.
ADT contains all required functionalities to create, compile, debug and deploy Android applications from the Eclipse IDE. ADT also allows to create and start AVDs.
ADT contains all required functionalities to create, compile, debug and deploy Android applications from the Eclipse IDE. ADT also allows to create and start AVDs.
The Android system uses a special virtual machine, i.e. the Dalvik Virtual Machine to run Java based applications. Dalvik uses an own bytecode format which is different from Java bytecode.
Therefore you cannot directly run Java class files on Android, they need to get converted in the Dalvik bytecode format.
Therefore you cannot directly run Java class files on Android, they need to get converted in the Dalvik bytecode format.
Android applications are primarily written in the Java programming language. The Java source files are converted to Java class files by the Java compiler.
The Android SDK contains a tool called dx which converts Java class files into a
These dex files are therefore much smaller in size than the corresponding class files.
The
The resulting
The Android Development Tools (ADT) performs these steps transparently to the user.
If you use the ADT tooling you press a button the whole Android application (
The Android SDK contains a tool called dx which converts Java class files into a
.dex (Dalvik Executable) file. All class files of one application are placed in one compressed .dex file. During this conversion process redundant information in the class files are optimized in the .dex file. For example if the same String is found in different class files, the .dex file contains only once reference of this String.These dex files are therefore much smaller in size than the corresponding class files.
The
.dex file and the resources of an Android project, e.g. the images and XML files, are packed into an .apk(Android Package) file. The program aapt (Android Asset Packaging Tool) performs this packaging.The resulting
.apk file contains all necessary data to run the Android application and can be deployed to an Android device via the adb tool.The Android Development Tools (ADT) performs these steps transparently to the user.
If you use the ADT tooling you press a button the whole Android application (
.apk file) will be created and deployed.
The ADT allows the developer to define certain artifacts, e.g. Strings and layout files, in two ways: via a rich editor, and directly via XML. This is done via multi-page editors in Eclipse. In these editors you can switch between both representations by clicking on the tab on the lower part of the screen.
For example if you open the
For example if you open the
res/layout/main.xml file in the Package Explorer View of Eclipse, you can switch between the two representations as depicted in the following screenshot.
The components and settings of an Android application are described in the
It must also contain the required permissions for the application. For example if the application requires network access it must be specified here.
The
Google Play requires that every Android application uses its own unique package. Therefore it is a good habit to use your reverse domain name as package name. This will avoid collisions with other Android applications.
The
The
The
AndroidManifest.xml file. For example all Activities and Services of the application must be declared in this file.It must also contain the required permissions for the application. For example if the application requires network access it must be specified here.
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="de.vogella.android.temperature" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".Convert" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion="9" /> </manifest>
The
package attribute defines the base package for the Java objects referred to in this file. If a Java object lies within a different package, it must be declared with the full qualified package name.Google Play requires that every Android application uses its own unique package. Therefore it is a good habit to use your reverse domain name as package name. This will avoid collisions with other Android applications.
android:versionName and android:versionCode specify the version of your application. versionName is what the user sees and can be any String.versionCode must be an integer. The Android Market determine based on the versionCode, if it should perform an update of the applications for the existing installations. You typically start with "1" and increase this value by one, if you roll-out a new version of your application.The
<activity> tag defines an Activity, in this example pointing to the Convert class in thede.vogella.android.temperature package. An intent filter is registered for this class which defines that this Activity is started once the application starts (action android:name="android.intent.action.MAIN"). The category definition category android:name="android.intent.category.LAUNCHER" defines that this application is added to the application directory on the Android device.The
@string/app_name value refers to resource files which contain the actual value of the application name. The usage of resource file makes it easy to provide different resources, e.g. strings, colors, icons, for different devices and makes it easy to translate applications.The
uses-sdk part of the AndroidManifest.xml file defines the minimal SDK version for which your application is valid. This will prevent your application being installed on unsupported devices.
The
These resources must be defined in the
If you create a new resource, the corresponding reference is automatically created in
The Android system provides methods to access the corresponding resource via these IDs.
For example to access a String with the
gen directory in an Android project contains generated values. R.java is a generated class which contains references to certain resources of the project.These resources must be defined in the
res directory and can be XML files, icons or pictures. You can for example define values, menus, layouts or animations via XML files.If you create a new resource, the corresponding reference is automatically created in
R.java via the Eclipse ADT tools. These references are static integer values and define IDs for the resources.The Android system provides methods to access the corresponding resource via these IDs.
For example to access a String with the
R.string.yourString ID, you would use thegetString(R.string.yourString)) method.R.java is automatically created by the Eclipse development environment, manual changes are not necessary and will be overridden by the tooling.
While the
res directory contains structured values which are known to the Android platform, the assetsdirectory can be used to store any kind of data. You access this data via the AssetsManager which you can access the getAssets() method.AssetsManager allows to read an assets as InputStream with the open() method.// Get the AssetManager AssetManager manager = getAssets(); // Read a Bitmap from Assets try { InputStream open = manager.open("logo.png"); Bitmap bitmap = BitmapFactory.decodeStream(open); // Assign the bitmap to an ImageView in this layout ImageView view = (ImageView) findViewById(R.id.imageView1); view.setImageBitmap(bitmap); } catch (IOException e) { e.printStackTrace(); }
The user interface for Activities is defined via layouts. The layout defines the included
A layout can be defined via Java code or via XML. In most cases the layout is defined as an XML file.
XML based layouts are defined via a resource file in the
If a
By conversion this will create and assign a new
Defining layouts via XML is usually the preferred way as this separates the programming logic from the layout definition. It also allows the definition of different layouts for different devices. You can also mix both approaches.
Views (widgets) and their properties.A layout can be defined via Java code or via XML. In most cases the layout is defined as an XML file.
XML based layouts are defined via a resource file in the
/res/layout folder. This file specifies theViewGroups, Views, their relationship and their attributes for this specific layout.If a
View needs to be accessed via Java code, you have to give the View a unique ID via the android:idattribute. To assign a new ID to a View use @+id/yourvalue . The following shows an example in which aButton gets the button1 ID assigned.<Button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Show Preferences" > </Button>
By conversion this will create and assign a new
yourvalue ID to the corresponding View. In your Java code you can later access a View via the method findViewById(R.id.yourvalue).Defining layouts via XML is usually the preferred way as this separates the programming logic from the layout definition. It also allows the definition of different layouts for different devices. You can also mix both approaches.
In your XML files, for example your layout files, you can refer to other resources via the
For example, if you want to refer to a color which is defined in a XML resource, you can refer to it via
@ sign.For example, if you want to refer to a color which is defined in a XML resource, you can refer to it via
@color/your_id. Or if you defined a "hello" string in an XML resource, you could access it via@string/hello.
The Android system controls the lifecycle of your application. At any time the Android system may stop or destroy your application, e.g. because of an incoming call. The Android system defines a lifecycle forActivities via predefined methods. The most important methods are:
onSaveInstanceState()- called after theActivityis stopped. Used to save data so that theActivitycan restore its states if re-startedonPause()- always called if theActivityends, can be used to release resource or save dataonResume()- called if theActivityis re-started, can be used to initialize fields
An
In the emulator you can simulate the change of the orientation via Ctrl+F11.
You can avoid a restart of your application for certain configuration changes via the
Activity will also be restarted, if a so called "configuration change" happens. A configuration change happens if an event is triggered which may be relevant for the application. For example if the user changes the orientation of the device (vertically or horizontally). Android assumes that an Activity might want to use different resources for these orientations and restarts the Activity.In the emulator you can simulate the change of the orientation via Ctrl+F11.
You can avoid a restart of your application for certain configuration changes via the
configChangesattribute on your Activity definition in your AndroidManifest.xml. The following Activity will not be restarted in case of orientation changes or position of the physical keyboard (hidden / visible).<activity android:name=".ProgressTestActivity" android:label="@string/app_name" android:configChanges="orientation|keyboardHidden|keyboard"> </activity>
The class
The Context also provides access to Android Services, e.g. the Location Service.
Activities and Services extend the
android.content.Context provides the connection to the Android system and the resources of the project. It is the interface to global information about the application environment.The Context also provides access to Android Services, e.g. the Location Service.
Activities and Services extend the
Context class.
The following assumes that you have already Java and Eclipse installed and know how to use Eclipse. For an introduction into Eclipse please see the following tutorial: Eclipse IDE Tutorial.
The tutorial above also describes how to install new components into Eclipse. This is required to install the Android Development Tools. You find the necessary steps described in the following section of the tutorial:Eclipse Update Manager.
The author of this text has also published a Kindle book on the usage of the Eclipse IDE, which can be found here: Eclipse IDE Book for Kindle.
The tutorial above also describes how to install new components into Eclipse. This is required to install the Android Development Tools. You find the necessary steps described in the following section of the tutorial:Eclipse Update Manager.
The author of this text has also published a Kindle book on the usage of the Eclipse IDE, which can be found here: Eclipse IDE Book for Kindle.
The Android SDK is 32bit, therefore on a 64bit Linux system you need to have the package
ia32-libsinstalled. For Ubuntu you can do this via the following command.apt-get install ia32-libsPlease check your distribution documentation, if you are using a different flavor of Linux.
Use the Eclipse update manager to install all available components for the Android Development Tools (ADT) from the URL https://dl-ssl.google.com/android/eclipse/.
After the new Android development components are installed, you will be prompted to install the Android SDK. You can use the following wizard or go to the next section to learn how to do it manually.
After the new Android development components are installed, you will be prompted to install the Android SDK. You can use the following wizard or go to the next section to learn how to do it manually.
After the installation of the ADT the Eclipse tooling allows to download the Android SDK automatically. Alternatively you can also manually download the Android SDK from the Android SDK download page.
The download contains a zip file, which you can extract to any place in your file system, e.g. on my Linux system I placed it under "/home/vogella/android-sdks". Avoid using spaces in the path name, otherwise you may experience problems with the usage of the Android SDK.
You also have to define the location of the Android SDK in the Eclipse Preferences. In Eclipse open the Preferences dialog via the menu → . Select Android and enter the installation path of the Android SDK.
The download contains a zip file, which you can extract to any place in your file system, e.g. on my Linux system I placed it under "/home/vogella/android-sdks". Avoid using spaces in the path name, otherwise you may experience problems with the usage of the Android SDK.
You also have to define the location of the Android SDK in the Eclipse Preferences. In Eclipse open the Preferences dialog via the menu → . Select Android and enter the installation path of the Android SDK.
The Android SDK Manager allows you to install specific versions of Android. Select → from the Eclipse menu.
The dialog allows you to install new packages and also allows you to delete them.
Select Available packages and open the Third Party Add-ons . Select the Google API 15 (Android 4.0.3) version of the SDK and press the button.
Press the button and confirm the license for all packages. After the installation completes, restart Eclipse.
The dialog allows you to install new packages and also allows you to delete them.
Select Available packages and open the Third Party Add-ons . Select the Google API 15 (Android 4.0.3) version of the SDK and press the button.
Press the button and confirm the license for all packages. After the installation completes, restart Eclipse.
During Android development it is very useful to have the Android source code available.
As of Android 4.0 the Android development tools provides also the source code. You can download it via the Android SDK Manager by selecting the Sources for Android SDK.
The sources are downloaded to the source directory located in
To connect the sources with the android.jar file in your Android project, right click on your android.jar in the Eclipse Package Explorer and select → . Type in the source directory name and press the button.
Afterwards you can browse through the source code.
As of Android 4.0 the Android development tools provides also the source code. You can download it via the Android SDK Manager by selecting the Sources for Android SDK.
The sources are downloaded to the source directory located in
path_to_android_sdk/sources/android-xx. xx is the API level of Android, e.g. 15 for the Android 4.0.4 version.To connect the sources with the android.jar file in your Android project, right click on your android.jar in the Eclipse Package Explorer and select → . Type in the source directory name and press the button.
Afterwards you can browse through the source code.
The Android Development Tools (ADT) include an emulator to run an Android system. The emulator behaves like a real Android device (in most cases) and allows you to test your application without having a real device.
You can configure the version of the Android system you would like to run, the size of the SD card, the screen resolution and other relevant settings. You can define several of them with different configurations.
These devices are called Android Virtual Device " and you can start several in parallel.
You can configure the version of the Android system you would like to run, the size of the SD card, the screen resolution and other relevant settings. You can define several of them with different configurations.
These devices are called Android Virtual Device " and you can start several in parallel.
During the creation of an AVD you decide if you want an Android device or a Google device.
An AVD created for Android will contain the programs from the Android Open Source Project. An AVD created for the Google API's will also contain several Google applications, most notable the Google Maps application.
If you want to use functionality which is only provided via the Google API's, e.g. Google Maps you must run this application on an AVD with Google API's.
An AVD created for Android will contain the programs from the Android Open Source Project. An AVD created for the Google API's will also contain several Google applications, most notable the Google Maps application.
If you want to use functionality which is only provided via the Google API's, e.g. Google Maps you must run this application on an AVD with Google API's.
The following shortcuts are useful for working with the emulator.
Alt+Enter Maximizes the emulator. Nice for demos.
Ctrl+F11 changes the orientation of the emulator.
F8 Turns network on / off.
Alt+Enter Maximizes the emulator. Nice for demos.
Ctrl+F11 changes the orientation of the emulator.
F8 Turns network on / off.
The graphics of the emulator can use the native GPU of the computer. This makes the rendering in the emulator very fast. To enable this, add the
You can also set the
GPU Emulation property to the device configuration and set it totrue.You can also set the
Enabled flag for Snapshots. This will save the state of the emulator and will let it start much faster. Unfortunately currently native GPU rendering and Snapshots do not work together.
To define an Android Virtual Device (ADV) open the AVD Manager dialog via → and press button.
Enter the values similar to the following screenshot.
Select the Enabled for Snapshots box. This will make the second start of the virtual device much faster.
Press the button. This will create the AVD configuration and display it under the Virtual devices.
To test if your setup is correct, select your device and press the button
After some time your AVD starts. Do not interrupt this startup process, as this might corrupt the AVD.
After the AVD started, you can use the AVD via the mouse and via the virtual keyboard of the emulator.
Enter the values similar to the following screenshot.
Select the Enabled for Snapshots box. This will make the second start of the virtual device much faster.
Press the button. This will create the AVD configuration and display it under the Virtual devices.
To test if your setup is correct, select your device and press the button
After some time your AVD starts. Do not interrupt this startup process, as this might corrupt the AVD.
After the AVD started, you can use the AVD via the mouse and via the virtual keyboard of the emulator.
Things are not always working as they should. This section gives an overview over typical problems and how to solve them.
Several users report that they get the following errors:
To solve any of these errors, go to the project menu and select → .
- Project ... is missing required source folder: 'gen'
- The project could not be built until build path errors are resolved.
- Unable to open class file R.java.
To solve any of these errors, go to the project menu and select → .
The communication with the emulator or your Android device might have problems. This communication is handled by the Android Debug Bridge (adb).
Eclipse allows to reset the adb in case this causes problems. Select therefore the DDMS perspective via → → →
To restart the adb, select the "Reset adb" in the Device
Eclipse allows to reset the adb in case this causes problems. Select therefore the DDMS perspective via → → →
To restart the adb, select the "Reset adb" in the Device
View.
The LogCat view shows you the log messages of your Android device and helps you to analyze problems. For example Java exceptions in your program would be shown here. To open this view, select → → → → .
If Android complains that you cannot use Java7 select your right-click on your project and select the Java Compiler entry. Ensure that Java 1.5 or Java 1.6 is used. You may have to select the Enable project specific settings checkbox.
Sometimes Eclipse complains that a file, e.g.
R.layout.main cannot be found. Check in your source code that you did not import android.R. An android.R import will prevent Eclipse from finding your R file.
Android provides nice editors to edit Android resource files, unfortunately these editor are not always automatically used due to bugs in the ADT. If that happens, you can open this editor manually. Right-click on your menu file and select → .
If your emulator does not start, make sure that the android-sdk version is in a path without any spaces in the path name.
If you face timeout issues during deployment you can increase the default timeout in the Eclipse preferences. Select → → → and increase the ADB connection timeout (in ms)value.
Sometimes the emulator will refuse to install an application with the error message: INSTALL_FAILED_INSUFFICIENT_STORAGE.
An Android virtual device provides by default only 64M for the storaging Android applications. You can clean your installed application by re-starting the emulator and selecting the Wipe user data " flag.
Alternatively you can set the data partition size. If you press edit on the AVD, you can set the
An Android virtual device provides by default only 64M for the storaging Android applications. You can clean your installed application by re-starting the emulator and selecting the Wipe user data " flag.
Alternatively you can set the data partition size. If you press edit on the AVD, you can set the
Ideal size of data partition property via the button.
If you get the error message Debug Certificate expired switch to the folder which contains the Android AVD, e.g.
.android under Linux and delete the debug.keystore file. This file is only valid for a year and if not present, Eclipse will regenerate the password.
The
@Override annotation was introduced in Java 1.6. If you receive an error message for @Override, change the Java compiler level to Java 1.6. To do this, right-click on the project, select → → and select 1.6 in the drop-down box.
Java requires that classes which are not part of the standard Java Language are either fully qualified or declared via imports.
If you see an error message with the XX cannot be resolved to a variable text, right-click in your
If you see an error message with the XX cannot be resolved to a variable text, right-click in your
Editor and select → to important required packages.
The tutorials of this document have been developed and tested with Android 4.0.4, API Level 15. Please use this version for all tutorials in this book. Higher versions of the API level should also work. A lower version of the Android API might also work, but if you face issues, try the recommended version.
The base package for the projects is always the same as the project name, e.g. if you are asked to create a project called de.vogella.android.example.test, then the corresponding package name isde.vogella.android.example.test.
The application name, which must be entered on the Android project generation wizard, will not be predefined. Choose a name you like.
The base package for the projects is always the same as the project name, e.g. if you are asked to create a project called de.vogella.android.example.test, then the corresponding package name isde.vogella.android.example.test.
The application name, which must be entered on the Android project generation wizard, will not be predefined. Choose a name you like.
The Android development tools show warnings, if you use hard-coded strings, for example in layout files. For real applications you should use String resource files. To simplify the creation of the examples, we use Strings directly. Please ignore the corresponding warnings.
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