Base.kt

class Base {
  
  var pizzaBaseType : String? = null
  
}

Pizza.kt

class Pizza {
  
  var topping : Topping? = null
  var base : Base? = null
  
  override fun onCreate(savedInstanceState: Bundle?) {
  super.onCreate(savedInstanceState)
  setContentView(R.layout.pizza_activity)
    
  toping = Topping()
  toping?.topingType = "Chicken"
  
  base = Base()
  base?.pizzaBaseType = "CheeseBurst"
  }
   
}

Topping.kt

class Topping {
  
  var toppingType : String? = null
  
}