What is the purpose of annotations in Jetpack Compose and how are they used?

In Jetpack Compose, annotations are used to provide additional information to the compiler and development tools, as well as to control the behavior of functions and UI components. For example, the @Composable annotation indicates a function that describes a part of the user interface and can be called within other composable functions.

Example of using the @Composable annotation:

@Composable
fun Greeting(name: String) {
    Text(text = "Hello, $name!")
}

Additionally, there are annotations for optimization, validation, state management, etc. They help make the code more readable and correct from the perspective of Compose.

Thus, annotations in Jetpack Compose serve to:

• Mark composable functions (@Composable)
• Manage state and effects (@Stable, @Immutable)
• Assist the compiler and tools in code analysis

They are used by adding them before the definition of functions or classes.