Mobile development remains one of the most popular areas in IT, and the platform Android continues to hold the lead in the number of active devices in the world. Despite the growing popularity of the language Kotlin, Java it is still the foundation of the ecosystem, on which millions of lines of code are written in existing projects. Studying development for Android in Java gives a deep understanding of how a virtual machine works Dalvik and ARTand also opens up access to a huge amount of legacy code and libraries.
The process of creating an application may seem complicated for a beginner due to the abundance of tools and specific architecture, but a consistent approach allows you to break the task into understandable steps. You will need to install a specialized development environment, understand the activity life cycle, and learn how to design user interfaces. In this article, we will go all the way from setting up the working environment to assembling a ready-made installation file.
Being willing to learn and having basic knowledge of object-oriented programming will significantly speed up the immersion process. Android SDK provides all the necessary tools for emulating the operation of the app on virtual devices, which eliminates the need to constantly connect a physical smartphone. Let's start by preparing your computer for use.
Preparing the development environment and installing tools
The first and most important step is installing the integrated development environment Android Studio. This is an official tool from Google that includes a code editor, emulator, debugger and interface designer. The distribution should be downloaded exclusively from the developer’s official website to avoid compatibility and security problems. After installation, the app will offer to download additional components, such as Android SDK Platform and an emulator.
During the setup process, you will be asked to select the installation type. For most users, the standard mode is suitable Standard, which automatically downloads the latest stable versions of the necessary packages. If you plan to develop for specific versions of Android or test on older devices, you should select Custom and manually select the required API versions.
⚠️ Attention: Make sure that virtualization is enabled on your computer in the BIOS/UEFI. Without this technology, the emulator will work extremely slowly or will not start at all, which will make testing the application impossible.
After installation is complete and the project is loaded for the first time, the environment will prompt you to create a new project. It is important to choose the right template here. A template Empty Activityis best suited to start learning, as it contains a minimal set of code and allows you to understand the structure of the project without unnecessary noise. Don't choose complex templates with navigation menus or maps until you master the basic principles.
Project structure and key configuration files
Understanding directory structure is critical to navigating the project. After creating a new project, you will see several key folders. The folder app/manifests contains a file AndroidManifest.xml, which is the passport of your application. It describes all components, such as activities and services, and also requests the necessary permissions to access the camera, the Internet or contacts.
The main application code is located in the folder app/java. This is where you will create classes in Java. The entry point is usually a class MainActivity, which inherits from the base class Activity. Application resources, including interface layouts, strings, colors, and images, are stored in the app/resfolder. Separating code and resources makes it easy to localize the application and change the design without rewriting the logic.
The build file build.gradle (app module level) manages the project dependencies. Here you connect external libraries that expand the functionality of your application. For example, to work with the network, a library is often connected Retrofit, and for loading images - Glide. The connection syntax is as follows:
dependencies {implementation 'androidx.appcompat:appcompat:1.6.1'
implementation 'com.google.android.material:material:1.9.0'
}
It is important to monitor the versions of the libraries you are connecting to, since version incompatibility can lead to compilation errors. The build system Gradle will automatically download all specified dependencies from the repositories when the project is first built. If you change this file, the project will need to be synchronized, which Android Studio will prompt you to do automatically.
Use the gradle.properties file to increase the amount of memory allocated to the project build, adding the line org.gradle.jvmargs=-Xmx2048m if the build fails with an OutOfMemory error.
Creating the user interface in XML
The interface of Android applications is described in markup language XML. Each screen corresponds to a separate XML file, which is visually displayed in the layout editor. The main container in which the elements are located is called ViewGroup. The most commonly used groups are LinearLayout for the linear arrangement of elements and ConstraintLayout for creating flexible interfaces with anchors.
Consider a simple example of creating a screen with text and a button. In the layout file, you add a widget TextView to display the title and Button to the user action. Each element can be given a unique name via the android:idattribute in order to subsequently access it from Java code. The parameters of width, height, indents and text are also set.
| UI element | Description | Frequent use |
|---|---|---|
TextView |
Text display | Headings, signatures, articles |
EditText |
Text entry field | Registration forms, search |
Button |
Button to press | Submitting forms, transitions |
ImageView |
Displaying images | Logos, photographs products |
To adapt the interface to different screens, it is recommended to use restrictions (constraints) in ConstraintLayout. This allows elements to “stick” to the edges of the screen or to each other, maintaining proportions on devices with different diagonals. The visual editor in Android Studio allows you to drag and drop elements with the mouse, automatically generating the necessary XML code.
Why can't you write an interface directly in Java?
Although it is technically possible to create View objects programmatically, using XML separates logic and presentation, simplifies the work of designers and allows the system to cache resources more efficiently.
Writing application logic in Java
Once the interface is ready, you need to “revive” it by writing logic in Java. In an activity class, a method onCreate is the entry point where initialization occurs. The first step is to bind Java objects to elements from the XML layout using the findViewByIdmethod. This method finds a view by its ID and returns a reference to it, which must be cast to the appropriate type.
Next you can app the reaction to user actions. The most common scenario is handling a button click. To do this, use the method setOnClickListener, into which an anonymous class or lambda expression is passed. Inside this handler, you describe the actions that should be performed when clicked, for example, changing the text or going to another screen.
Button myButton = findViewById(R.id.my_button);myButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// Logic for processing the click
Toast.makeText(MainActivity.this, "Button pressed!", Toast.LENGTH_SHORT).show();
}
});
The class Toastis often used to display short messages to the user. It shows a pop-up notification that disappears after a few seconds. This is a convenient way to debug or inform the user about the result of an action without interrupting his work. Also in this section you can implement mathematical calculations, working with strings and conditional logic.
⚠️ Warning: Never perform long operations, such as network requests or reading large files, in the main thread (UI Thread). This will cause the interface to freeze and an error to appear
ANR(Application Not Responding).
Working with activities and transitions between screens
Most applications consist of several screens, which in Android are called Activity. The transition from one screen to another is carried out using the object Intent. An intent is a message to the system that you want to launch another component. You create an intent, specifying the current context and the class of the target activity, and then call the method startActivity.
Often there is a need to transfer data from one screen to another. For example, when you select a product in the list, you need to open a screen with its detailed description. To do this, additional data is added to the object Intent through the method putExtra. In the receiving activity, this data is retrieved in the method onCreate using getIntent().getStringExtra() or similar methods for other data types.
☑️ Checklist for transitioning between screens
The life cycle of an activity is the sequence of states that the screen goes through: creation, start, pause, stop, and destruction. Understanding the onPause, onStop and onDestroy methods is necessary to correctly save data and free up resources. For example, if the user has minimized the application, it goes into a pause state, and you must stop playing the video or animation.
Building the project and launching it on the device
When the code is written and the interface is designed, the testing stage begins. You can run the application on a virtual device (emulator) created in AVD Manager, or connect a real smartphone via USB. To connect a real device, you need to enable the USB Debugging mode on it in the "For Developers" menu. The computer will recognize the device and it will appear in the list of launch targets.
The APK file build process is managed by the Gradle system. To create a release version ready for publication, use the build command Build > Generate Signed Bundle / APK. You will need to create a signing key (Keystore), which will cryptographically verify the authorship of the application. Losing this key will make it impossible to update the application in the future under the same name.
After successful assembly, you will receive a file with the extension .apk, which can be installed on any Android device. During the build process, the system also checks the code for linter errors, indicating potential performance or security issues. Correcting linter warnings before publishing is considered good development practice.
Signing an application with a Keystore key is a mandatory and irreversible step for publication in the store; keep the key file in a safe place.
Frequently asked questions for beginning developers
Do I need to know Kotlin if I am learning Java for Android?
Knowledge Kotlin is becoming increasingly desirable as Google positions it as the language of choice. However, Java remains fully supported, and many large projects are written in it. Knowledge of Java will give you a foundation that can easily be transferred to Kotlin later.
Why is my emulator running very slowly?
Most often the problem is disabled virtualization (VT-x or AMD-V) in the computer BIOS. The emulator also requires the allocation of sufficient RAM. Try creating a device with a lower screen resolution or using a physical smartphone for tests.
How to add an application icon?
Icons are stored in a folder res/mipmap. Android Studio has a tool Image Asset Studio (available by right-clicking on the res folder) that automatically generates icons of all required sizes and densities from one source image.
What is Gradle Sync Failed?
This error means that the build system was unable to load dependencies or the project settings are incorrect. Check your Internet connection, library versions in build.gradle and try clearing the cache through the menu File > Invalidate Caches / Restart.