Developing and testing applications for the Android platform requires a clear understanding of how source code is turned into a working software product. For many novice developers, the question of how exactly the process of initializing and launching an application written in the language occurs remains unclear. There are many nuances, from choosing the right development environment to the operating features of emulators. Java, remains unclear. There are many nuances, ranging from choosing the right development environment to the operating features of emulators.
Understanding launch mechanisms is critical not only for creating new projects, but also for debugging existing errors. If you plan to create complex Android applicationss, you will have to deal with setting up the JDK, SDK and configuring Gradle correctly. Without correctly setting up these components, it is impossible to run the code, even if it is syntactically perfect.
In this article we will analyze in detail all the stages of preparing the environment, write a simple example of code and consider various ways of executing it. We'll cover topics on using Android Studio, the command line, and physical devices. You will learn how to avoid common mistakes and optimize the development process.
Preparing the development environment and installing the JDK
The first step towards creating a working application is installing the Java Development Kit. Most modern versions Android Studio come with a built-in version of the JDK, but professional development often requires installing a separate, up-to-date version. Make sure that you download the distribution from the official Oracle website or use open-source analogues like OpenJDK.
After installation, you need to configure environment variables in your operating system. This will allow the compiler and build tools to find Java executables from any directory. For Windows, this is done through system properties, and for Linux and macOS, through editing shell profile files.
Use the java -version command in the terminal to ensure that the system sees the installed version of the JDK and that it matches the requirements of your version of Android SDK.
It is important to monitor version compatibility. Some older libraries may not work correctly with the latest versions of Java, while modern language features require fresh updates. Check the documentation for the compiler you are using support librariesto choose the optimal version of the compiler.
⚠️ Attention: Never install multiple versions of the JDK at the same time without clearly managing the JAVA_HOME environment variables, as this can lead to conflicts when building the project and unpredictable compilation errors.
Setting up Android Studio and creating a project
The Android Studio integrated development environment is the industry standard for creating mobile applications. When you launch it for the first time, the setup wizard will prompt you to install additional components, including Android SDK and the emulator. Failure to install these components at this stage will complicate further work, so it is recommended to accept the default proposal.
To create a new project, select the "Empty Activity" template. In the configuration window, specify the application name, package (domain name) and programming language. Despite the popularity of Kotlin, the choice Java is still relevant for supporting legacy code and specific corporate tasks. Make sure that the Minimum SDK version matches the target audience of your application.
☑️ Setting up a new project
The structure of the created project may seem complicated to a beginner, but the key files are in the directory app/src/main/java. This is where the main code of your application resides. The file AndroidManifest.xml plays the role of an application passport, describing its components and necessary permissions.
The Gradle build system will automatically pull up all the necessary dependencies specified in the file build.gradle. If you plan to use third-party libraries, they must be added to this file. After making changes, be sure to click the button Sync Nowto update the project.
Code structure and application entry point
Unlike console apps in Java, where the entry point is a method main, in Android the application life cycle is managed by the system through Activity components. The main class of your application must inherit from class Activity or its modern analogues. A method onCreate is an analogue of a constructor where the interface is initialized.
Inside a method onCreate you must call the method setContentViewpassing it the interface layout identifier. Without this call, nothing will be displayed on the device screen, and the user will only see a black screen or an error. This is a fundamental rule of Android architecture.
public class MainActivity extends Activity {@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
Interaction with interface elements is carried out through the method findViewById. Once you have a reference to an object, you can assign event handlers, change text, or hide elements. All operations with the UI must be performed on the main thread, otherwise the application will crash.
Why can't you create a UI in the constructor?
The constructor is called before the Activity context is fully initialized by the system. Attempting to access resources or context in the constructor may result in a NullPointerException or incorrect application behavior.
Building the project and generating the APK file
The process of turning the source code into an installation file is called building. In Android Studio, this is done automatically every time you start it, but you can initiate it manually through the menu Build -> Build Bundle(s) / APK(s) -> Build APK(s). The result of this operation will be a file with the extension .apk, ready for installation.
The build system performs several stages: compiling Java code into bytecode, converting it to the Dalvik Executable (DEX) format, packaging resources and signing the application with a debug key. A signature is required to identify the author and ensure the integrity of the code.
| Build phase | Process description | Resulting file |
|---|---|---|
| Compilation | Converting .java to .class | Class files |
| Dexing | Conversion to Android format | classes.dex |
| Resourcing | Image and XML processing | resources.arsc |
| Signature | Adding a cryptographic signature | Signed APK |
For debug versions, an automatically generated key is used, stored in a hidden user folder. To publish to the Google Play Store, you must create your own signing key and store it securely. Losing the key will make it impossible to update an already published application.
The debug APK is only suitable for testing on emulators and personal devices; publication in the store requires a release build with its own signature.
Running on an emulator and physical device
The fastest way to check the functionality of the application is to use the built-in emulator. Android Studio allows you to create virtual devices with different screen characteristics, Android version, and memory size. The launch is done by pressing the green button Run in the toolbar.
However, the emulator does not always reflect the real behavior of the application, especially in matters of performance and working with sensors. Connecting a physical device requires enabling the mode USB debugging in the developer settings on the smartphone. This item is hidden by default and is activated by pressing the build number seven times in the "About phone" menu.
- 📱 Connect the device with a cable to the computer and select the file transfer mode.
- 🔓 Unlock the smartphone screen and confirm the debugging request in the dialog box that appears window.
- 🖥️ Select your device from the list of available devices in Android Studio before starting.
If the device does not appear in the list, check the installed drivers. Devices from some manufacturers require the installation of specific USB drivers. Also make sure that the cable is working and supports data transfer, not just charging.
⚠️ Attention: On devices with custom firmware (MIUI, Flyme, etc.), additional permissions in the "For Developers" menu may be required, such as "USB debugging (security settings)" or disabling MIUI optimization.
Debugging and analyzing application logs
Even a thoroughly tested application may contain errors that only appear under certain conditions. The Logcat tool in Android Studio allows you to view system logs in real time. Filtering by your app tag helps you filter out unnecessary information and focus on your own messages.
To output debugging information, class calls are inserted into the code Log. The Log.d method is used for debug messages, Log.e for errors, and Log.i for an information record. Analysis of the call stack (stack trace) when an application crashes is the main method of finding the causes of the failure.
Log.d("MyApp", "The application launched successfully");try {
// Dangerous operation
} catch (Exception e) {
Log.e("MyApp", "An error occurred: " + e.getMessage());
}
Using breakpoints allows you to pause code execution and analyze variable values step by step. This is a powerful tool for finding logic errors that do not cause an obvious crash, but lead to incorrect interface behavior.
How to speed up Logcat?
Use regular expressions in the Logcat filter field to display only lines containing your package keywords or specific error codes.
Frequently asked questions
Why does the application close immediately after launch?
The most likely reason is an unhandled exception in the onCreate method or an attempt to access a non-existent interface resource. Check the logs in Logcat, find the line with the error type "FATAL EXCEPTION" and analyze the call stack.
Is it possible to run a Java application without Android Studio?
Yes, it is possible via the command line using the sdkmanager, adb and gradle CLI tools. However, this process requires deep knowledge of the SDK structure and manual configuration of paths, which is not recommended for beginners.
How to transfer an application from Java to Kotlin?
Android Studio has a built-in code converter. You can open the Java file and select Code -> Convert Java File to Kotlin Filefrom the menu. The conversion is successful in 90% of cases, but manual checking of the logic is still necessary.
What to do if the emulator is very slow?
Make sure that virtualization (VT-x or AMD-V) is enabled in your computer's BIOS. Also, allocate more RAM to the emulator in the AVD Manager settings and use system images marked Google APIs Play Store.