Jetpack Compose definition
Jetpack Compose is Android's modern declarative UI toolkit, built by Google in Kotlin. Developers write composable functions that describe the interface for the current state, and Compose redraws only the parts that change when data updates. It replaces XML layouts and the View system as Google's recommended way to build Android user interfaces.
How does Jetpack Compose work?
A Compose interface is built from Kotlin functions annotated with @Composable. Layout composables such as Column, Row, Box and LazyColumn arrange content, modifiers control size, padding, clicks and drawing, and Material 3 components provide buttons, cards, navigation bars and dialogs. Compose reached its stable 1.0 release in 2021 and is now the default for new Android projects in Android Studio templates.
State is held with remember and mutableStateOf, or comes from a ViewModel exposing a StateFlow. When state changes, Compose re-runs only the composable functions that read it, a process called recomposition. Hoisting state up to a parent keeps composables simple and testable. Android Studio previews render composables in the editor with different themes, fonts and screen sizes.
Jetpack Compose vs XML views
The older View system splits UI between XML layout files and Kotlin or Java code that finds views and updates them. Compose keeps everything in Kotlin, removes view binding boilerplate, and makes theming, lists and animation much shorter to write. Adapters for RecyclerView, for example, become a few lines in a LazyColumn.
Migration does not require a rewrite. ComposeView embeds Compose inside existing XML screens, and AndroidView hosts classic views, such as a map or ad view, inside Compose. Most teams migrate gradually, writing new screens in Compose and converting old ones when they need significant changes anyway.
Key Jetpack Compose features
- Material 3 components and dynamic color theming.
- Declarative animation APIs for visibility, size, color and shared elements.
- Navigation Compose for type-safe routes and deep links.
- Lazy lists and grids for efficient scrolling.
- Semantics for accessibility and for UI tests.
- Compose for Wear OS and Android TV.
- Testing APIs that find composables by text or semantics and simulate user input.
- Adaptive layouts for foldables, tablets and Chromebooks.
- Compose Multiplatform from JetBrains, which extends the model to iOS (stable since 2025) and desktop.
Performance tips and pitfalls
Most Compose performance problems come from unnecessary recomposition. Passing unstable objects or lambdas that change on every frame forces composables to rerun, and reading fast-changing state, such as scroll position, too high in the tree recomposes large sections of the screen. Use keys in lazy lists, read state as late as possible and check recomposition counts in the Layout Inspector.
Always measure release builds, since debug builds run Compose noticeably slower. Baseline profiles, generated with Macrobenchmark, precompile critical code paths and improve startup and scrolling. R8 shrinking and optimization should be enabled for production. Test startup and scrolling on a mid-range phone, not only on a flagship device.
When to use Jetpack Compose
For new native Android apps, Compose is the clear default and matches Google's guidance, documentation and new libraries. For existing apps, adopt it screen by screen. Nexzem builds Android apps in Kotlin with Compose and Material 3, profiles release builds on mid-range devices before launch, and uses Compose Multiplatform when clients want to share interface code with iOS.