What structure does the Dagger dependency injection tool have?

Dagger is a static dependency injection framework for Android and Java. Its structure is based on the following key components:

• @Module — a class that provides dependencies through methods annotated with @Provides.
• @Component — an interface that connects modules and injection points. The component generates code to create and provide objects.
• @Inject — an annotation used to indicate injection points (such as constructors, fields, or methods).

Example:

@Module
class NetworkModule {
    @Provides
    OkHttpClient provideOkHttpClient() {
        return new OkHttpClient();
    }
}

@Component(modules = NetworkModule.class)
interface AppComponent {
    void inject(MainActivity activity);
}

public class MainActivity extends AppCompatActivity {
    @Inject
    OkHttpClient client;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        DaggerAppComponent.create().inject(this);
        // Now client is initialized by Dagger
    }
}

Thus, Dagger builds a dependency graph at compile time, which improves performance and code safety.