Jetpack Compose

Jetpack Compose is a tool from Google used to build user interfaces for Android apps. User interface means everything the user sees and can touch on the screen: buttons, texts, lists, input fields. In the past, you had to maintain two separate things for this: an XML file that describes the appearance, and a Kotlin or Java file that controls the behavior. Jetpack Compose turns this into a single thing. You write Kotlin code – a widely used programming language for Android – and within it directly describe what should appear on the screen. Google officially released Compose in 2021 and has since recommended it as the preferred way to build new Android apps.

Why Compose changed Android development

The old system, known as the View system, dates back to 2008 – the year Android was released. It was patched and extended over many years. The result: a lot of code for simple tasks, and many places where errors could occur. A button with text and color needed a good 20 lines of XML plus additional Kotlin code. In Compose, it’s often five.

Another advantage is what’s known as state management. In the past, a developer had to manually tell the system: “Update this text now.” Compose flips this around. You describe once what should be displayed when a certain state applies – for example: “If the user is logged in, show their name.” If the state changes, Compose automatically adjusts the interface. This significantly reduces a common source of errors.

The building principle: Composables stack like building blocks

The basic building block in Compose is called a Composable – pronounced “com-POH-zuh-bul.” This is a perfectly normal Kotlin function that you mark with @Composable. It describes a small part of the interface, for example a single button or a line of text. Large interfaces are created by nesting such functions inside one another.

Imagine you’re building a profile section in an app. You write a Composable for the profile picture, one for the name, one for the follow button. You put these three into a parent Composable called ProfileCard. The ProfileCard then ends up on a screen, which is itself a Composable too. This layering principle is called declarative: you describe the result, not every single step to get there. This is the opposite of the older, imperative style, where you instruct step by step what to do.

When the user presses a button, Compose only recalculates the parts of the interface that have actually changed. This process is called recomposition. It is targeted and efficient, so that the app stays smooth.

Jetpack Compose in apps, news, and job postings

Many well-known Android apps already rely on Compose. Google itself has partially or fully switched Play Store, Maps, and Gmail to Compose. Twitter – now X – and Airbnb have publicly described how they migrated their apps. Anyone starting a new Android app today will almost always encounter Compose, because Google presents it as the standard in its learning materials and templates.

In tech news, Compose mainly comes up at Android developer conferences, such as Google I/O, which takes place every spring. New Compose features are presented there. In job postings for Android developers, too, “Jetpack Compose” has been one of the most frequently mentioned keywords since 2022 – anyone who wants to build Android apps can hardly avoid the term.

A common misconception: Jetpack Compose does not replace Kotlin, but builds on top of it. Compose is not a separate framework that you learn instead of a programming language – it is a library, meaning a collection of ready-made tools that you integrate into Kotlin code. The term Jetpack, in turn, refers to an entire family of such libraries from Google for Android, ranging from database management to navigation between screens.