Applying accumulate on subclass in drools

I am creating the object of stock and inserting stock values as below

1. Customer 1 has 2 stocks stocks4 and stocks5
2. customer2 has 1 stocks arrayListStocks1

Here I am trying to make sum of all Stocks for given session

Stocks stocks1=new Stocks("stock1", 1, 1);
            Stocks stocks2=new Stocks("stock2", 2, 2);

            Stocks stocks4=new Stocks("stock4", 4, 4);
            Stocks stocks5=new Stocks("stock5", 5, 5);

            ArrayList<Stocks> arrayListStocks1=new ArrayList<Stocks>();
            arrayListStocks1.add(stocks1);
            arrayListStocks1.add(stocks2);


            Customer customer1= new  Customer();
            customer1.setCustomerName("ACC");
            customer1.setStocks(arrayListStocks1);

            ArrayList<Stocks> arrayListStocks2=new ArrayList<Stocks>();
            arrayListStocks2.add(stocks4);
            arrayListStocks2.add(stocks5);


            Customer customer2= new  Customer();
            customer2.setCustomerName("JINDAL");
            customer2.setStocks(arrayListStocks2);

            kSession.insert(customer1);
            kSession.insert(customer2);


rule "Rule5"
 // agenda-group "promotions2"
dialect "java"
no-loop
salience 80
    when
         $list: List() from collect($customer:Customer($customerName:customerName,$stk:stocks))
         $customer:Customer($customerName:customerName,$stk:stocks)
         $stocks:Stocks() from $stk
         $listStocks: List() from collect(Stocks($stockNumber:stockNumber > 1) from $stk )
         $sum:Number() from accumulate (Stocks($stockNumber: stockNumber) from $stk,sum($stockNumber))
    then
       // System.out.println("Rule5 Stock Number- " + $stocks.getStockNumber());
       // System.out.println("Rule5  SIZE - " + $listStocks.size());
        System.out.println("Number - " +  $sum);
end

when I run above rule I am getting below output Number - 9.0 Number - 9.0 Number - 3.0 Number - 3.0

how to calculate sum of 2 stocks from customer1 and customer2 I am expecting the result 12

Thanks,

If all you want to do is to calculate the sum of all the stock for all the customers, then you can try something like this:

rule "Stocks Sum"
when
  $n: Number() from accumulate(
    Customer($stk:stocks) and
    Stocks($stockNumber: stockNumber) from $stk,
    sum($stockNumber)
  )
then
  //...
end

Hope it helps