Annotations in Kotlin allow developers to add metadata to their code. These annotations can be used for a variety of purposes, such as code generation, reflection, and more. In this post, we will take a closer look at the Annotation class in Kotlin and how it can be used in your code.

The Annotation class in Kotlin is a special kind of class that can be applied to other elements of your code, such as classes, functions, and properties. These annotations can be used to provide additional information about the element to which they are applied. For example, you might use an annotation to indicate that a certain function should only be called on the main thread or to indicate that a certain property should be serialized to JSON.

To create an annotation class in Kotlin, you simply need to prefix the class declaration with the @ symbol. For example, the following code defines an annotation called MainThread:

@Target(AnnotationTarget.FUNCTION)
annotation class MainThread

The @Target annotation is used to specify the elements to which this annotation can be applied. In this case, the MainThread annotation can only be applied to functions.

Once you have defined an annotation class, you can use it in your code by applying it to the relevant elements. For example, the following code applies the MainThread annotation to a function:

@MainThread
fun doSomething() {
    // code here
}

annotation class MyAnnotation(val value: String)

@MyAnnotation("Hello")
fun doSomething() {
    // code here
}

You can also use the @field:MyAnnotation or @get:MyAnnotation to annotate fields or getters respectively.

Annotations can also be used in conjunction with reflection to inspect the code at runtime. For example, you might use reflection to find all the functions in your code that are annotated with the MainThread annotation, and then ensure that they are only called on the main thread.

In summary, annotations in Kotlin provide a powerful way to add metadata to your code and can be used for a variety of purposes such as code generation, reflection, and more. The Annotation class in Kotlin is the base class for creating annotation and it allows you to create custom annotations and apply them to elements of your code.