Creating and Targeting Custom Annotations
Define annotations with retention policies and apply them to classes, functions, and properties.
Why Custom Annotations?
Annotations are metadata attached to declarations (classes, functions, properties, parameters). Custom annotations let you mark code for processing by frameworks, build tools (KSP/KAPT), or your own runtime logic.
Declaring an Annotation
Use the annotation class keyword. Annotation classes can have constructor parameters (only primitive types, String, KClass, enums, other annotations, or arrays thereof):
annotation class Validate(val minLength: Int = 1, val maxLength: Int = 255)All lessons in this course
- Kotlin Reflection: KClass, KFunction, KProperty
- Creating and Targeting Custom Annotations
- Reading Annotations at Runtime
- Reflection-Based Validation and Mapping