Global exception handling in Spring uses @ControllerAdvice to centralize error responses across all controllers. I define @ExceptionHandler methods for specific exceptions, returning consistent error DTOs with HTTP status codes. Custom exceptions exte

Spring Data JPA eliminates boilerplate DAO code with repository interfaces. I extend JpaRepository to get CRUD methods automatically—save, findById, findAll, delete. Custom query methods use method naming conventions—findByEmailAndActiveTrue generates

Java Streams provide a functional approach to processing collections with operations like filter, map, and reduce. I use stream() to create streams from collections and apply intermediate operations that are lazy and return new streams. Terminal opera

Spring Boot simplifies building production-ready REST APIs with minimal configuration. I use @RestController to create RESTful endpoints and @RequestMapping to define routes. The @GetMapping, @PostMapping, @PutMapping, and @DeleteMapping annotations h

Android performance optimization ensures smooth 60fps UI and efficient resource usage. I use Android Profiler to monitor CPU, memory, network, and energy. Layout Inspector identifies overdraw and deep view hierarchies. Systrace captures system-level t

ProGuard and R8 shrink, obfuscate, and optimize Android apps for release builds. R8 is the default tool, combining shrinking and desugaring. I configure rules in proguard-rules.pro—keeping classes used by reflection, serialization, or native code. -ke

Deep links open specific app content from external sources. I configure intent filters in AndroidManifest with URL schemes—http, https, or custom. App Links verify ownership via assetlinks.json on your domain, providing seamless no-dialog opening. Int

Google Play Billing enables selling digital content and subscriptions. I integrate the Play Billing Library and initialize BillingClient with PurchasesUpdatedListener. Query available products with queryProductDetailsAsync(). Launch purchase flow with

Services run background operations without UI. I extend Service and override onStartCommand() for started services or onBind() for bound services. Foreground services use startForeground() with ongoing notification, required for long-running tasks vis

Notification channels give users granular control over notification types on Android 8+. I create channels with unique IDs, names, and importance levels. Channels group related notifications—messages, reminders, promotions. Users control vibration, so

App Widgets display app content on the home screen. I extend AppWidgetProvider, a BroadcastReceiver subclass handling widget lifecycle. onUpdate() refreshes widget UI, onEnabled() initializes on first widget added, onDisabled() cleans up when last rem

BroadcastReceiver responds to system-wide or app-specific events. I register receivers statically in AndroidManifest or dynamically with registerReceiver(). The onReceive() method handles broadcasts—network changes, battery status, boot completed, SMS