Development of mobile applications on platform Android remains one of the most popular areas in the IT industry, despite the active implementation of the language Kotlin. Java still is the foundation of the ecosystem, ensuring the stability of millions of existing projects and providing a deep understanding of how a virtual machine Dalvik or ARTworks. For a novice developer, choosing this language means access to a huge array of documentation and time-tested architectural solutions.
However, the process of writing code for Android is significantly different from creating desktop applications or server systems. The limitations of the mobile operating system, component lifecycle management, and specific memory optimization requirements are critical here. In this article, we'll take a closer look at how to set up your environment, understand the basic principles, and start writing efficient code that will work on smartphones and tablets.
Preparing a professional development environment (IDE)
The first step towards creating a quality application is to install an integrated development environment. The Android Studioplatform-based IntelliJ IDEAhas been considered an industry standard for many years. It provides all the necessary tools: from smart code completion to a powerful device emulator. The distribution should be downloaded exclusively from the developer’s official website to avoid licensing and security problems.
After installation, you need to configure it correctly Software Development Kit (SDK). It is a set of tools, libraries and documentation needed to compile and run applications. In the SDK Manager inside the development environment, you should select the specific version of the platform Androidfor which you will write code, as well as the build tools Build-Tools. It is important to make sure that the package Android SDK Platform-Toolscontaining utilities adb for debugging on real devices is installed.
Project configuration also plays a decisive role. When creating a new project, the wizard will prompt you to select the minimum SDK version (minSdkVersion). This setting determines which devices your app can run on. The lower the version, the wider the audience coverage, but the fewer modern APIs will be available for you to use.
☑️ Checking the readiness of the environment
⚠️ Attention: Versions of the build tools and compiler may change with the release of new Android Studio updates. Always check version numbers against Google's official documentation to avoid dependency conflicts in the file
build.gradle.
Android App Architecture Basics
Understanding architecture is key to writing maintainable code. Unlike regular Java apps, where an Execution begins with a main()method, an Android application consists of a set of components whose life cycle is managed by the operating system. The main building blocks are Activities, which represent a separate screen with a user interface, and Services, which perform background operations.
Each component has a strictly defined sequence of states. For example, Activity goes through the stages of creation, start, resumption, pause, stop and destruction. The developer is required to override the appropriate callback methods, such as onCreate(), onStart() or onDestroy(), in order to correctly save the application state and free resources.
Interaction between components is carried out through special objects - Intents. They allow you to launch other activities, transfer data between them, or initiate system actions, such as opening the camera or browser. Incorrect use of intents can lead to memory leaks or application crashes when the screen is rotated.
What is a Manifest file?
AndroidManifest.xml is a configuration file that tells the system about the components of your application, required permissions and SDK versions. Without correctly registering an activity in the manifest, the system simply will not know about its existence and will not be able to launch it.
The MVC pattern or its variations, such as MVVM, are often used to organize logic. This helps separate the user interface from the business logic, making the code more readable and testable. Using ViewModel allows you to save data when changing the device configuration, which is a common problem when developing for Android.
Creating an interface: XML and Layouts
The visual part of the application is described in markup language XML. Layout files are stored in a directory res/layout and define the hierarchy of View objects that the user sees on the screen. Each interface element, be it a button Button or a text field TextViewcorresponds to a class in Java code.
The modern approach to layout involves the use of flexible containers. ConstraintLayout allows you to create complex interfaces with a flat hierarchy, which has a positive effect on performance rendering. Unlike outdated LinearLayout With multiple nesting, this constraint manager adapts to different screen sizes without the need to create dozens of alternative layouts.
Binding XML markup to Java code occurs through the method findViewById() or, in newer versions, through the ViewBinding mechanism. Having received a reference to an element, the developer can programmatically change its properties, set event handlers and update content in real time.
| UI element | Purpose | Frequency of use |
|---|---|---|
TextView |
Text display | Critical high |
Button |
Action control element | High |
RecyclerView |
Display data lists | High |
EditText |
User text input field | Medium |
Working with data and asynchrony
Mobile applications rarely work in isolation; they constantly need access to a network, database, or file system. Performing such operations in the main thread (UI Thread) is strictly prohibited, as this leads to blocking of the interface and the appearance of an error ANR (Application Not Responding). To solve this problem, Java uses multithreading mechanisms.
The traditional approach was to use classes AsyncTask, but they are now considered obsolete. Modern standards dictate the use of libraries Retrofit for network queries and Room for working with a local SQLite database. These tools automatically perform heavy operations on background threads and return the result to the main thread through callback or LiveData mechanisms.
Lambda expressions and interfaces that appeared in new versions of Java are also actively used to control threads. This allows you to write more concise code for processing asynchronous tasks. For example, loading an image from the Internet can be implemented in several lines using the library Glide or Picasso.
⚠️ Attention: Never store sensitive data (passwords, tokens) in SharedPreferences in clear text. Use encrypted storage or Android Keystore to protect user information.
Use Facebook's Stetho library or Android Studio's built-in database inspector to view SQLite content in real time while debugging. This will save hours on writing debug logs.
Debugging and testing code
The process of writing code is inextricably linked with finding and correcting errors. The Logcat tool in Android Studio is the main source of information about the operation of the application. It displays system logs, error messages and debug outputs that the developer adds using the class Log. Correctly setting up filters allows you to quickly find the required records in a stream of thousands of events.
To check the functionality of individual modules, you need to write unit tests (Unit Tests) using the framework JUnit. They run quickly and do not require an emulator, allowing you to test the calculation logic and data processing. To test the user interface, there are instrumental tests that run on a real device or an emulator.
Debugger allows you to execute code step by step, stopping at breakpoints. This is an indispensable tool for analyzing the state of variables at a specific point in time. You can change variable values on the fly and see how this affects further app execution.
Log.d("MainActivity", "Variable value: " + variableValue);
It is also important to test on different device configurations. The emulator allows you to simulate different versions of Android, screen sizes and amounts of RAM. However, tests on real hardware devices remain mandatory, since the emulator cannot fully reproduce the behavior of a specific processor or radio module.
Regular coverage of the code with tests reduces the number of bugs in production by 40-50% and simplifies refactoring in the future.
Building and publishing the application
The final stage of development is preparing the release version of the application. The build system Gradle compiles Java source code into bytecode, optimizes resources and packages all files into APK or AAB (Android App Bundle) format. To publish to the Google Play Store, using the AAB format is a mandatory requirement, as it allows the store to generate optimized APKs for each specific user device.
The build process includes the step of obfuscation of the code using a tool ProGuard or R8. This makes the source code unreadable to attackers and reduces the size of the resulting file by removing unused classes and methods. Setting up obfuscation rules requires care so as not to remove elements necessary for reflection or serialization to work.
Before release, you must sign the application with a digital key. This key confirms the authorship of the developer and allows you to release updates for an application already installed by users. Losing the signing key means it is impossible to update the application, so storing it requires maximum security.
What is the difference between Debug and Release builds?
Debug builds include debugging information, are not obfuscated and have lower performance, but allow you to use debugging tools. The release build is optimized for speed and size, signed with the developer key and ready for publication in the store.
Is it possible to write in pure Java without XML?
Yes, the entire interface can be created programmatically in Java by creating View objects and adding them to the hierarchy manually. However, this complicates code maintenance and separation of responsibilities between design and logic, so using XML or Jetpack Compose is the standard.
What is the minimum version of Java required for Android?
Modern versions of Android Studio and Gradle require at least Java 11, and for new features it is recommended to use Java 17. Older projects can run on Java 8, but support for legacy versions is gradual is terminated.
Why do you need the build.gradle file?
This is a build configuration script that specifies project dependencies, plugin versions, compiler settings, and signing parameters. It manages the entire process of turning source code into a finished application.