Deep Copy of List element and recursion - java

Question

I have a Trade class with 3 parameters (amount, description, date). The amount of each trade cannot be greater than maxAmount.

I have many trades saved in a ListToSend, and some of the amounts exceed the maxAmount limit, so I need to split those trades into multiple trades before sending the list.

I thought about working with two lists, my original ListToSend and a tradesToSplit list. Basically I want to:

1. Move each splitableTrade from ListToSend to tradesToSplit.
2. Then I want to loop over tradesToSplit and for every trade in there :
   • I call a recursiveMethod that is going to divide the amount by 2 and:
     • if amount/2 is not greater than maxAmount :
       • Then I create a newTrade, which is essentially a deep copy of the initial trade, and I set the newTrade amount to be originalAmount/2.
       • if not, I keep dividing the amount by calling recursiveMethod

But I'm stuck here as I have no idea how to edit the original trade after many iteration of recursiveMethod.

Is there a better way to achieve what I'm trying to do ?

Answer 1

in OOP it is recommended to keep objects immutable because immutable objects are inherently thread-safe, easier to debug (you can share the object reference without worrying about unexpected or unauthorized changes), etc.

In your case I would create a function splitTrade that would take a trade of any amount and return a list of trade where each amount is less than maxAmount.

Here is some pseudo java code:

private List<Trade> splitTrade(Trade trade, List<Trade> acc) {
  if (trade.getAmount() > Trade.MAX_AMOUNT) {
    Trade trade1 = new Trade(Trade.MAX_AMOUNT, trade.getDescription(), trade.getDate());
    Trade trade2 = new Trade(trade.getAmount() - Trade.MAX_AMOUNT, trade.getDescription(), trade.getDate());
    acc.add(trade1);
    return splitTrade(trade2, acc);
  } else {
    acc.add(trade);
    return acc;
  }
}

public List<Trade> splitAllTrades(List<Trade> listToSend) {
  return listToSend.stream().flatMap((t) -> splitTrade(t, new ArrayList<Trade>()).stream().toList();
}

without the lambda syntax:

public List<Trade> splitAllTrades(List<Trade> listToSend) {
  List<Trade> validTrades = new ArrayList<>();
  for (Trade trade: listToSend) {    
    validTrades.addAll(splitTrade(trade, new ArrayList<Trade>()));
  }
  return validTrades;
}