Mobile ecosystem Android remains one of the most popular platforms for developers around the world. Despite the growing popularity of the language Kotlin, the programming language Java still forms the basis of millions of existing applications and is actively used in the corporate sector. Understanding how to write code in Java for this platform opens up access to a huge market for mobile devices and allows you to support legacy projects.
The process of creating mobile software requires not only knowledge of the language syntax, but also a deep understanding of the architecture of the operating system. You will work with unique components, such as Activity, Service and BroadcastReceiverthat manage the life cycle of the app. This distinguishes mobile development from the creation of desktop utilities or web services, where the logic of work is often more linear and predictable.
In this article we will look at the entire path from installing the necessary software to publishing the finished product in the store Google Play. We will look at the key features of interface layout, user event processing and interaction with smartphone hardware. Being ready to dive into the world of object-oriented programming and mobile technologies will be your first step towards creating your own digital products.
Preparing the work environment and installing tools
The first step towards creating an application is to install an integrated development environment Android Studio. This is the official IDE from Google, which provides all the necessary tools for writing code, debugging and emulating devices. The distribution package should be downloaded exclusively from the official website of the developer in order to avoid problems with security and version compatibility.
After installation, you will need to configure Android SDK (Software Development Kit), which contains libraries and tools for compiling code for different versions of the operating system. In the SDK manager, you need to select the target versions Androidfor which you plan to develop. It is recommended to install at least one stable version of the system and an emulator image for testing.
A critical point is the choice of version JDK (Java Development Kit). Modern versions Android Studio often come with a built-in version JDKhowever, complex projects may require manual configuration of the path to the external Java installation. Incorrect configuration of compilation error paths, so you should carefully check the settings in the menu File → Project Structure → SDK Location.
⚠️ Attention: Versions of tools Gradle and plugin Android must be strictly compatible with each other. If, after updating the environment, the project no longer builds, check the configuration files
build.gradleand check the versions with the official compatibility table.
☑️ Ready for development
Project structure and main components
When creating a new project, the environment generates a standard directory structure that must be understood to work effectively. Focus on the folder app/src/main, where all source code and resources are stored. The file AndroidManifest.xml is the passport of your application: it describes all components, access rights and hardware requirements.
The language code Java is located in a directory java and is organized into packages. Each application screen is usually a separate class that inherits from the base class Activity. It is in this class that the logic of user interaction, processing of button clicks and data management is described.
Application resources, such as images, strings and interface layouts, are stored in the folder res. The separation of code and resources makes it easy to adapt the application to different languages and screen sizes without changing the app logic. The use of resource identifiers, such as R.layout.activity_main, ensures type safety when accessing interface elements.
| Component | Purpose | Life cycle |
|---|---|---|
| Activity | Single interface screen | Managed by the system |
| Service | Background operation | Long-term |
| BroadcastReceiver | Reaction to events | Short-term |
| ContentProvider | Data management | By request |
What is an R-class?
The R-class is generated automatically and contains links to all project resources. Never edit this file manually, as it will be overwritten during the next compilation.
Creating an interface using XML
The visual part of the application on Android is described using markup language XML. This approach allows you to separate the design from the operating logic, which simplifies the maintenance and modification of the code. Each interface element, be it a button or a text field, is an object of a class View or its descendant.
For arranging elements, special containers are used, called Layouts. The most common are LinearLayout, which arranges elements sequentially, and ConstraintLayout, which allows you to create complex adaptive interfaces with linking elements to each other. Choosing the right layout affects rendering performance and usability on different screens.
Each interactive element must be assigned a unique identifier using the attribute android:id. This is the link between XML markup and Java code. Without an identifier, it will be impossible to programmatically access a button or input field, which will make the interface static and non-functional.
- 📱 TextView —used to display text information to the user.
- 🔘 Button —an interactive element for triggering actions when clicked.
- 🖼️ ImageView —component for displaying graphic images and icons.
- 📝 EditText —an input field that allows the user to enter text.
Use string files (strings.xml) for all text in the interface. This will simplify the localization of the application into other languages in the future and eliminate the hardcode of lines in the code.
Writing logic in Java
After creating the layout, you need to animate the interface using code in Java. The connection between XML and code is established in the onCreatemethod, which is called when the activity is created. Here we use the setContentViewmethod, which loads the corresponding markup file.
To access interface elements, we use the findViewByIdmethod, which returns a reference to the object by its identifier. The resulting object must be converted to the desired type, for example, (Button) or (TextView). Only then can you assign event listeners, such as OnClickListener to handle clicks.
Attempt to change text in TextView from a background thread will cause an exception and crash the application. For long-running operations, such as loading data from the network, you should use separate threads or asynchronous tasks.
Button myButton = findViewById(R.id.my_button);myButton.setOnClickListener(new View.OnClickListener {
@Override
public void onClick(View v) {
// Click processing logic
Toast.makeText(MainActivity.this,"Pressed!", Toast.LENGTH_SHORT).show;
}
});
⚠️ Attention: Never store direct links to
VieworContextactivities in static fields. This leads to memory leaks, since the garbage collector will not be able to free resources even after the screen is closed.
Data handling and persistence state
Mobile applications rarely work without data, so it is important to understand the mechanisms for storing them. For simple settings and user preferences, the SharedPreferencesmechanism is used. It is a key-value store and is ideal for storing the state of radio buttons or the last selected item.
A local database is used to store more complex structured data SQLite. In an ecosystem, working with it is often abstracted through a library, which simplifies writing queries and checking their correctness at the compilation stage. This allows you to avoid many mistakes associated with manually writing SQL queries. Android working with it is often abstracted through a library Room, which simplifies writing queries and checking their correctness at the compilation stage. This allows you to avoid many of the mistakes associated with manually writing SQL queries.
Particular attention should be paid to maintaining the activity state when the device configuration changes, for example, when the screen is rotated. By default, the activity is destroyed and recreated, which may result in the loss of user input. To prevent this, you need to override the method onSaveInstanceState and restore the data to onCreate.
Using the MVVM (Model-View-ViewModel) architecture helps separate the logic for working with data from the interface code, making the application more testable and maintainable.
Debugging, testing and publishing
The debugging process in Android Studio provides powerful tools for analyzing the operation of the application. You can set breakpoints, step through code, and inspect variable values in real time. System operation logs are displayed in a window Logcatwhere you can filter messages by tags and severity level.
Before releasing the application, it is necessary to conduct testing on real devices with different versions Android and screen diagonals. Emulators are useful in the early stages, but only real hardware will show problems with performance, heating or sensor operation. Pay special attention to the operation of the application when there is insufficient RAM.
To be published in Google Play the application must be signed with a digital release key. This key is stored in a file keystore and must be securely stored, since its loss will make it impossible to update the application in the future. The release build process differs from the debug version by optimizing the code and removing debugging information.
- 🚀 MinifyEnabled — enabling code obfuscation to reduce the size of the APK.
- 🔐 Signing Config — setting up a digital key for signing the application.
- 📦 Bundle — Android App Bundle publishing format instead of APK.
⚠️ Attention: Store policies Google Play and API level requirements are regularly updated. Before publishing, be sure to check the latest requirements in the developer console, as applications with an outdated targetSdkVersion may be rejected.
What is ProGuard?
ProGuard is a tool that removes unused code and renames classes to obscure names to make reverse engineering more difficult and reduce file size applications.
Do I need to know Kotlin if I write in Java?
Knowledge Kotlin is not strictly required to support existing Java projects, but is highly desirable for new development. Many modern libraries and code examples are written directly in Kotlin, and understanding both languages will make you a more versatile specialist.
What is the minimum version of Android supported?
Technically, you can configure the project to support very old versions, starting from Android 2.3. However, for publication in Google Play there are restrictions: the application must support current versions of the system, and the use of outdated APIs may be blocked.
How to translate an application into another language?
For localization, you need to create files strings.xml in resource folders with language suffixes, for example values-es for Spanish or values-fr for French. The system will automatically substitute the required text depending on the language settings on the user's device.
Is it possible to develop for Android on a regular PC?
Yes, to develop for Android a regular computer with an operating system is sufficient Windows, macOS or Linux. Having a physical smartphone is not necessary, since you can use the built-in emulator, although testing on a real device is always preferable.