How to count the number of objects created in Kotlin? - kotlin

Question

In the following code snippet i have created 4 instances of CompanionClass and want to know how many
instances i have created , so have tried many ways but didn't work. Here i used companion object class
to keep track of objects but i know it has no connection with objects because keepTrackOfObjects() is
static. Can anyone help me solve this, please?
class CompanionClass
{
companion object{
var numberOfObjects = 0
fun keepTrackOfObjects() = println("number of created objects currently is: +
${++numberOfObjects}")
}
}
fun main()
{
val obj1 = CompanionClass()
CompanionClass.keepTrackOfObjects()
val obj2 = CompanionClass()`enter code here`
val obj3 = CompanionClass()
val obj4 = CompanionClass()
CompanionClass.keepTrackOfObjects()
}
// output is
// 1
// 2

Answer 1

You can use the init block to count the elements you created:
class CompanionClass {
companion object {
var counter: Int = 0
fun counter(): Int {
return counter
}
}
init {
counter++
}
}
You can test the behavior in this kotlin playground.

Answer 2

The problem is with your companion Object,
var numberOfObjects = 0
will initialise the variable every time you create a new instance. So create this variable in a separate class where keep all static content and use it from there. then you companion object will be like this.
companion object{
fun keepTrackOfObjects() = println("number of created objects currently is: +
${++numberOfObjects}")
}

Answer 3

To achieve this, you should increment your numberOfObject in a init statement.. Get a look at the code below
class User (var firstName:String,var lastName:String){
companion object {
var numberofinstance:Int = 0
fun getNumberOfInstance() = println("Nombre d'instance = $numberofinstance")
}
init {numberofinstance++}
}
Now you can use it in your main function
fun main(){
val user1=User("bob","marley")
val user2=User("bonkey","reynard")
val user3=User("jobbs","steve")
val user4=User("bill","naim")
val user5=User("jeff","romain")
User.getNumberOfInstance()
}
Output : Number of instance = 5