A `companion object` inside a class hosts what other languages call "static" members. Methods + properties on the companion are callable as `Foo.bar()`, but unlike static, they're a real object you can extend or implement interfaces on.
Kotlin
class User private constructor(val id: Long, val name: String) {
companion object {
private var nextId = 0L
fun create(name: String): User = User(++nextId, name)
const val MAX_NAME_LENGTH = 50
// Companion objects can implement interfaces too
}
}
fun main() {
val u = User.create("Alice") // calls companion factory
println("${u.id} ${u.name}")
println(User.MAX_NAME_LENGTH) // 50
// Java callers see this as a static field:
// User.Companion.create("Alice") — by default
// User.create("Alice") — with @JvmStatic on the function
}Save your own code snippets
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