this
- Kotlin course
- Beginner
- Lesson 110/116
- 5 min
Learn to access the class itself with this.
this: the current object
The this keyword refers to the current instance inside a method. When a parameter name clashes with a property name, you use this to tell them apart.
class Person(var name: String) {
fun rename(name: String) {
this.name = name
}
}this.name refers to the property, name to the parameter. The assignment copies the parameter into the property. Using this is not required when there is no clash.
When is this needed?
this is only required when a parameter clashes with a property name. If there is no clash, Kotlin finds the property automatically.
class Person(var name: String) {
fun rename(newName: String) {
name = newName // no need for this
}
}newName does not clash with name, so this can be skipped. When there is a clash, this is mandatory; otherwise the assignment goes to the wrong place. You can still use this for clarity even without a clash.
Practice Add a set method to Person
Define class Person(var name: String); in its body add fun set(name: String) { this.name = name }. In main create val p = Person("Ayşe"), call p.set("Alex") and print p.name with println.
Starter code
fun main() {
// Define a Person class with a name property and set method
// set must use this to separate the parameter
// Create an instance, change name with set, print
}Sample solution
class Person(var name: String) {
fun set(name: String) {
this.name = name
}
}
fun main() {
val p = Person("Ayşe")
p.set("Alex")
println(p.name)
}Expected output
Alex
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Fill in the blank: assign with this
class Person(var name: String) {
fun set(name: String) {
____.name = name
}
}class Person(var name: String) {
fun set(name: String) {
this.name = name
}
}Explanation: this.name refers to the property.
2 When is this used?
- When a parameter clashes with a property name Correct answer
- Always
- Never
- Only in static methods
Explanation: answer: when a parameter clashes with a property name. this separates them.
3 Match expression to meaning
| Term | Meaning |
|---|---|
this.name |
Property access |
name |
Parameter |
this |
Current object |
= name |
Assignment |