simple ArrayList Scala

import scala.reflect.ClassTag

object ArrayList{
  var counter = 0
  var increaseFactor = 2
  var size = 0;
}

class ArrayList[T: ClassTag](private var initialSize: Int = 5) {
  ArrayList.size = initialSize
  var arr = new Array[T](5)

  def size:Int = ArrayList.counter

  def isEmpty:Boolean = ArrayList.counter == 0

  def amortizedArray:Unit = {
    var newArr = new Array[T](ArrayList.size*ArrayList.increaseFactor)
    var i = 0

    while (i < size)
     {
       newArr(i) = arr(i)
        i = i+1
     }

    arr = newArr
    ArrayList.size = ArrayList.size*ArrayList.increaseFactor
  }
  def add(elem: T) =
    {
      if (ArrayList.counter == ArrayList.size)
        amortizedArray

      arr(ArrayList.counter) = elem
      ArrayList.counter+=1
    }

  def add(index: Int, elem: T): Unit =
  {
    if(index < 0 || index > ArrayList.counter)
      throw new IndexOutOfBoundsException("Invalid index")

    if (ArrayList.counter == ArrayList.size)
      amortizedArray

    var i = index
    val helpArr = new Array[T](ArrayList.counter - index)

    while (i < ArrayList.counter)
      {
        helpArr(i-index) = arr(i)
        i+=1
      }


    ArrayList.counter+=1
    val tmpIndex= index + 1
    i = tmpIndex

    while (i < ArrayList.counter) {
      arr(i) = helpArr(i - tmpIndex)
      i+=1
    }

    while (i < ArrayList.counter)
     {
       val tmp = arr(i+1)
       arr(i+1) = tmp
      i+=1
     }

    arr(index) = elem
  }

  def print : Unit=
    {
      var i = 0
      while(i < ArrayList.counter)
        {
          println(arr(i))
          i+=1
        }

      println("")
    }

  def contains (elem: T) : Boolean =
    {
      arr.contains(elem)
    }

  def remove (index: Int) : Unit =
    {
      if(index < 0 || index >= ArrayList.counter)
        throw  new IndexOutOfBoundsException("Invalid index")

      ArrayList.counter-=1

      var i = index
      while(i < ArrayList.counter)
        {
          arr(i) = arr(i+1)
          i+=1
        }

    }

}


object Tester {
  def main(args: Array[String]):Unit = {
    val arrayList = new ArrayList[Int]()
    println(arrayList.isEmpty)

    arrayList.add(1)
    arrayList.add(2)
    arrayList.add(3)
    arrayList.add(4)
    arrayList.add(5)
    arrayList.add(6)

    arrayList.print

    arrayList.add(2, 99)

    arrayList.print

    println(arrayList.contains(99))
    println(arrayList.contains(3))

    println(arrayList.isEmpty)

    arrayList.remove(2)

    arrayList.print
  }
}