How to check if an argument of an object is in an ArrayBuffer filled with objects in Scala? - scala

Question

I want to check if an Int typed by an user exists as primary argument/variable(the class has only one argument of type Int) in an ArrayBuffer filled with objects of a class.
It's an assignment for school, and I'm not able to get help of a prof or assistant so I'm asking for your help. I have to code a class "ewallet", which has attributes like "client id"(Int) and "pin code" (random Int between two Numbers). I'm not using "pin code" as an argument of the class as it seems to be implied in the assignment as it says "It has to show the pass when the user creates an account using his client id". I shouldn't be able to create 2 ewallets with the same client id.
So I would have to refuse to create an ewallet when if an ewallet with the same client id exists already in the ArrayBuffer (or array) that stocks ewallets.
Because of the Randomly generated "pin code", it creates different ewallets with same client id and different pin codes. So how to not add an ewallet(class) to a list if an ewallet with some argument exists already?
Thanks for helping a newbie.
I could just created another array list saving the client id's entered by an user and save them to compare with future client id's. But I'd like to learn how to do with an array containing objects.
I tried with for (i <- ListClients) if (NumClient != i.id) but if the list is empty, it doesn't do anything...
class ewallet(clientID: Int){
val id = clientID
val pass = 100 + Random.nextInt((99999-100)+1) //for the class, I didnt include the rest as its not related.
//for the main
def main(args: Array[String]): Unit = {
var ListClients = ArrayBuffer[ewallet]()
var action: Char = " ".charAt(0)
do {
println("[c]-Create ewallet. \n[a]-Access ewallet.\n[q]-Quit")
action = StdIn.readChar()
if (action == 'c') {
val NumClient = StdIn.readLine("Enter your client id :").toInt
var newClient = new ewallet(NumClient)
for (i <- ListClients) if (NumClient == i.id) {
println("Impossible, already exists.")
}
for (i <- ListClients) if (NumClient != i.id){
ListClients += newClient
println("Your pin code is : " + newClient.pass)
}
}
println(ListClients.mkString("\n"))
} while(action != 'q')
I should be able to add newClient to ListClients if NumClient != i.id, but because it's initially empty, it doesn't read those lines… So it does Nothing.

Answer 1

The simplest way would be to assign the result of the presence check to a variable, and add or "not add" the client object based on this variable. In Scala, the idiomatic way to work with collections are their rich set of transformation methods; in your case, exists provides the solution:
val alreadyExists = ListClients.exists(_.id == NumClient)
if (alreadyExists) {
println("Impossible, already exists.")
} else {
ListClients += newClient
println("Your pin code is : " + newClient.pass)
}
If you don't know yet about collection transformations and higher-order functions in general (and you should! they make life a lot easier), then the above piece is actually equivalent to this:
var alreadyExists = false
for (i <- ListClients) {
alreadyExists = alreadyExists || i.id == NumClient
}
(albeit a bit more efficient since it stops the iteration right after the existing client is found, if it is at all present).
As an unrelated comment, in Scala it is conventional to name variables in pascalCase and types in CamelCase. Thus, your class should be called something like EWallet, and variables like ListClients should be called listClients. Also, " ".charAt(0) is the same as ' '.