KProperty
- Kotlin course
- Advanced
- Lesson 62/83
- 5 min
Learn property info with KProperty.
Property info with KProperty
KProperty holds a reference to a property. It is obtained with ::propertyName. name gives the property name; get(instance) gives the value.
Example: class User(val name: String). val prop = User::name. prop.name returns "name". prop.get(User("Alex")) gives "Alex". This pattern reads property values at runtime.
Reading values with get
KProperty.get(instance) reads a property value. For class properties the instance is required; for top-level properties it is not.
Example: val u = User("Alex"); val v = User::name.get(u). This returns "Alex". get provides dynamic access at runtime; it is slower than compile-time access but flexible.
Practice Read a User property
Define class User(val name: String). In main create val u = User("Alex"), get the reference val prop = User::name and call println(prop.get(u)).
Starter code
// User class: name property
// in main create u, get prop reference, print its valueSample solution
class User(val name: String)
fun main() {
val u = User("Alex")
val prop = User::name
println(prop.get(u))
}Expected output
Alex
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the KProperty reference
class User(val name: String)
val prop = User____class User(val name: String)
val prop = User::nameExplanation: ::name gives a KProperty reference.
2 Which method reads a class property value via KProperty?
KProperty.get(instance) gives the value.- get(instance) Correct answer
- call()
- invoke()
- apply()
Explanation: get(instance) gives the property value.
3 Match the KProperty parts
| Term | Meaning |
|---|---|
User::name |
Property reference |
prop.name |
Property name |
prop.get(u) |
Value read |
val u = User(...) |
Instance |