Kotlin Reflection - GeeksforGeeks

09 Sep, 2021
Reflection is a set of language and library features that provides the feature of introspecting a given program at runtime. Kotlin reflection is used to utilize class and its members like properties, functions, constructors, etc. at runtime. Along with Java reflection API, Kotlin also provides its own set of reflection API, in a simple functional style. The standard Java Reflection constructs are also available in Kotlin and work perfectly with its code. Kotlin reflections are available in: 
kotlin.reflect package
It gives access to properties and nullable typesKotlin reflection has some additional features to Java reflection.kotlin reflection helps in accessing the JVM code, written by a language 
It gives access to properties and nullable types
Kotlin reflection has some additional features to Java reflection.
kotlin reflection helps in accessing the JVM code, written by a language 
To obtain, a class reference at runtime which is statically known, use the class reference operator. Also, the reference to a class can also be obtained from the instances of the class, such references are known as bounded class references. Using instances, you obtain the reference to the exact type to which the object conforms to, in case of inheritance. Example to demonstrate Class references 
Java
// A sample empty classclass ReflectionDemo {} fun main(){    // Reference obtained using class name    val abc = ReflectionDemo::class    println("This is a class reference $abc")     // Reference obtained using object    val obj = ReflectionDemo()    println("This is a bounded class reference ${obj::class}")}
Output 
This is a class reference class kotlin1.com.programmingKotlin.chapter1.ReflectionDemo
This is a bounded class reference class kotlin1.com.programmingKotlin.chapter1.ReflectionDemo 
We can obtain a functional reference to every named function that is defined in Kotlin. This can be done by preceding the function name, with the :: operator. These functional references can then be used as parameters to other functions. In the case of overloaded functions, we can either explicitly specify the type of the function, or it can be implicitly determined from the content.Example to demonstrate Functional References 
Java
fun add(a: Int,b: Int) : Int{    return a+b;}  fun add(a: String,b: String): String{    return """$a$b"""}  fun isDivisibleBy3(a: Int): Boolean{    return a%3 == 0}fun main(){    // Function reference obtained using :: operator    val ref1 = ::isDivisibleBy3    val array = listOf<Int>(1,2,3,4,5,6,7,8,9)    println(array.filter(ref1))      // Function reference obtained for an overloaded function    // By explicitly specifying the type    val ref2: (String,String) -> String = ::add;    println(ref2)      // Function reference obtained implicitly    val x = add(3,5)    println(x)}
Output 
[3, 6, 9]
fun add(kotlin.String, kotlin.String): kotlin.String
8 
We can obtain property reference in a similar fashion as that of function, using the :: operator. If the property belongs to a class than the classname should also be specified with the :: operator. These property references allow us to treat a property as an object that is, we can obtain there values using get function or modify it using set function.Example to demonstrate Property References 
Java
class Property(var a: Float){}  val x = 10;  fun main(){    // Property Reference for a package level property    val z = ::x    println(z.get())    println(z.name)      // Property Reference for a class property    val y = Property::a    println(y.get(Property(5.899f)))}
Output 
10
x
5.899 
The references to constructors of a class can be obtained in a similar manner as the references for methods and properties. These references can be used as references to a function which returns an object of that type. However, these uses are rare.Example to demonstrate Constructor References 
Java
class Property(var a: Float){}fun main(){    // Constructor Reference    val y = ::Property    println(y.name)}
Output 
<init>
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