Object Object Object

What is object

The object keyword in Kotlin defines something like class. But you cannot create instance of an object, as there is only one. Remember Singleton pattern.

object One {
  val n = 1
}

print(One.n) // 1

Interesting things about object

If you want to confine the object within the current file, you can make it as private. However, you cannot provide a parameter list for an object. Naming conventions is a little different for creating instance of object. What happens when you create an object? Kotlin defines the class and create a single instance of that class. Therefore, instead of starting a lower-case for first letter for instance of class, we use the upper-case for first letter, just like the class.

open class School(val noOfStudents: Int)

object University: School(1000)

interface SchoolOpening {
  fun open(): String
}

object OpenSchool: SchoolOpening {
  override fun open() = "Time to open"
}

Nested Object

Object could not be placed inside functions, but it can be nested inside other object or class.

object Outer {
  object Nested {
    val a = "Outer.Nested.a"
  }
}