Development of mobile applications for the platform Android is one of the most in-demand skills in the modern IT industry. Despite the growing popularity of the Kotlin language, Java remains the fundamental basis of the ecosystem on which millions of existing projects and libraries are built. Learning to create applications in this language provides a deep understanding of the operating system architecture and the principles of object-oriented programming.
The process of creating a app begins long before the first line of code is written. You will need to prepare a working environment, install specialized software, and understand the structure of a typical project. In this article, we'll go all the way from setting up the tools to running your first one on a physical device or emulator. Being willing to learn and having a basic knowledge of Java syntax will greatly speed up the immersion process. However, even beginners will be able to understand the material if they consistently follow the steps of the instructions. Let's start with the most important stage - preparing developer tools. «Hello World» on a physical device or emulator.
Being willing to learn and having a basic knowledge of Java syntax will greatly speed up your immersion process. However, even beginners will be able to understand the material if they consistently follow the steps of the instructions. Let's start with the most important stage - preparing the developer tools.
Preparing the working environment and installing Android Studio
The first step towards creating mobile software is installing an integrated development environment (IDE). The official and most powerful tool from Google is Android Studio. This environment includes all the necessary components: a code editor, a visual interface designer, a device emulator and a debugger.
The installation process requires care, since the distribution takes up a significant amount of disk space. After downloading the installer from the official website of the developer, you must follow the installation wizard. It is critically important not to uncheck the boxes for installing the emulator and system images if you plan to test applications without connecting a real smartphone.
⚠️ Attention: Android Studio requires at least 8 GB of RAM for correct operation, although 16 GB and an SSD drive are highly recommended for comfortable development. The project will take an unacceptably long time to assemble on the HDD.
After installation is completed, the first time you launch it, you will need to configure the SDK (Software Development Kit). The SDK manager allows you to select the versions of Android for which you will develop. The minimum API version for new projects in 2026-2026 is usually set to no lower than API 21 (Android 5.0), which covers more than 95% of active devices.
It is also important to check the availability of the Java Development Kit (JDK). Modern versions of Android Studio have their own JDK (JBR) built in, so a separate Java installation may not be required, but understanding the paths to executable files will be useful when debugging complex build scripts.
Use the "Darcula" theme in the Editor → Color Scheme settings to reduce eye strain during long programming sessions.
Project structure and basics components
When you create a new project through the menu File → New → New Project and select a template Empty Activity, the environment generates a complex hierarchy of files. Understanding the purpose of each folder is key to successfully navigating your code. You will do most of your work in the directory app/src/main.
Inside this folder there are two critical elements: the application manifest and the source code. The file AndroidManifest.xml describes the project configuration for the Android system. Everyone is registered here Activity, the necessary permissions to access the Internet or the camera are indicated, and the icon and name of the application are also determined.
The Java source code is located in a package, the name of which usually corresponds to the domain of your site in reverse order (for example, com.example.myapp). This is where the classes that describe the logic of the screens are located. Nearby is a folder res (resources), containing XML interface markup, string resources, images and styles.
Separation of code and resources is a fundamental principle of the Android architecture. This allows you to easily adapt the application to different languages and screen sizes by simply creating alternative folders in resources, without touching the logic in Java.
Writing the code for the first application
Let's consider creating a simple application that displays text on the screen and responds to button presses. Open the file MainActivity.java. This class inherits from AppCompatActivity, which ensures compatibility with modern interface standards.
Inside the method onCreate the activity is initialized. Here you call a method setContentView(R.layout.activity_main)that associates Java code with an XML markup file. Without this line, the user will see a black screen, since the system will not know which interface to display.
public class MainActivity extends AppCompatActivity {@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button myButton = findViewById(R.id.button_id);
myButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// Click processing logic
}
});
}
}
The method findViewByIdis used to interact with interface elements. It finds the widget based on its unique ID specified in the XML. In the example above, we find a button and attach an event listener to it OnClickListener. This is a standard pattern for processing user input.
Inside the block onClick you can place any code: opening a new screen, saving data or mathematical calculations.
☑️ Check before launch
Working with interface layouts (Layouts)
The appearance of the application is described in files with extension .xmllocated in the folder res/layout. Android Studio provides a visual editor that allows you to drag and drop elements with the mouse, but professionals often prefer to edit the XML code manually for greater accuracy and control.
The main building blocks are ViewGroup (containers) and View (widgets). Containers, such as LinearLayout, ConstraintLayout or RelativeLayout, define rules for the placement of child elements. Today ConstraintLayout is the most flexible and recommended choice for creating complex adaptive interfaces.
Each element has a set of attributes, such as android:layout_width, android:text or android:background. Width and height values can be fixed (in .dp), pad the parent (match_parent) or adjust to the content (wrap_content).
⚠️ Note: Interfaces may change in new versions of Android. Always check how your XML markup looks on different screen sizes using the Preview tool in the sidebar studio.
For text elements, never write text directly in XML. Use string resource references in the format @string/name_textThis allows you to store all text in a file strings.xml and easily translate the application into other languages in the future.
Activity lifecycle and state handling
One of the most difficult topics for beginners is understanding the Lifecycle of an activity. An activity is one screen of an application, and it can be in different states: created, running, stopped, destroyed or resumed.
The Android system can destroy your activity at any time, for example, when you rotate the screen or run out of memory. To ensure that the application does not lose user data, it is necessary to correctly handle callback methods. The main ones are: onStart, onResume, onPause, onStop and onDestroy.
Method onSaveInstanceState allows you to save the temporary state of the interface before possible destruction of the activity. The data is saved to an object Bundlewhich is then passed back to onCreate or onRestoreInstanceState.
What happens when the screen is rotated?
By default, when the device orientation changes, the activity is completely destroyed and recreated. This is needed to load alternative layouts (layout-land). If you don't save the user's input into input fields, it will be lost.
Understanding exactly when each method is called helps avoid memory leaks and replay errors. For example, heavy resources should be released in onStop, and event subscriptions should be updated in onResume.
Debugging, building and running on the device
After writing the code, the testing stage begins. You can run the application on a virtual device (emulator), which simulates the operation of a real phone, or connect your smartphone via a USB cable. To connect a real device, you need to enable the mode "USB Debugging" in the developer settings on the phone.
Android Studio provides a powerful Logcat tool for viewing system logs. If an application crashes, Logcat displays a Stack Trace pointing to the line of code where the failure occurred. Searching by tag FATAL EXCEPTION helps to quickly localize the problem.
For the final transfer of the application to users, the release version assembly procedure is performed. In the menu Build → Generate Signed Bundle / APK you create a signed file. Signing with a digital key is required for publication on Google Play and guarantees the authorship of the developer.
| Build type | Purpose | Optimization | Debugging |
|---|---|---|---|
| Debug | Testing during development | Disabled | Enabled (Logcat, debugger) |
| Release | Publish to store | Full (ProGuard/R8) | Disabled |
| Profile | Performance analysis | Partial | Enabled (Instrumentation) |
Always test the application on a real device before release, as the emulator may not reproduce specific problems with hardware or drivers.
The process of building the Release version includes code obfuscation (protection against reverse engineering) and removal of unused resources. This reduces the size of the final APK file and increases the security of your product.
Frequently asked questions by beginning developers
Do I need to know Kotlin if I'm learning Java for Android?
Knowledge of Kotlin is a big advantage, as Google positions it as a priority language. However, Java is fully supported, and a huge part of the legacy code is written in it. It is acceptable to start with Java, this will give you the foundation, but in the future it is worth learning Kotlin.
Why does my application crash immediately upon launch?
The most common reason is an error NullPointerException or ResourcesNotFoundException. Check Logcat. Often the problem lies in the fact that you access the interface element before the call setContentView or use the wrong resource ID.
How to add a third-party library to the project?
The modern way is to use the Gradle build system. You need to open the file build.gradle (app module level) and add the dependency to the block dependencies format implementation 'com.example:library:version', then click Sync.
How long does it take to create the first application?
If you have basic programming knowledge, creating a simple prototype (calculator, task list) can take from 2 to 5 days of intensive work. Learning the environment and the first concepts usually takes the first week.