Java流API-还原过程中的复杂计算

Question

是否有一些更好的方法在减少方面进行更复杂的计算（检查getCurrentbalance）：

@Override
    public Map<User, BigDecimal> getTotalExpensesForUsers(Group group) {
        return group.getExpenses().stream()
                .collect(Collectors.groupingBy(
                        Expense::getUser,
                        Collectors.reducing(BigDecimal.ZERO, Expense::getAmount, BigDecimal::add)
                ));
    }

    @Override
    public Map<User, BigDecimal> getCurrentBalance(Group group) {
        final var defaultTotalWeight = BigDecimal.valueOf(group.getDefaultTotalWeight());
        var totalExpensesPerUser = getTotalExpensesForUsers(group);
        final var averageExpensePerUser = totalExpensesPerUser.values().stream()
                .reduce(BigDecimal.ZERO, BigDecimal::add)
                .divide(defaultTotalWeight);

        totalExpensesPerUser.entrySet()
                .forEach(e -> e.setValue(e.getValue().subtract(averageExpensePerUser)));
        return totalExpensesPerUser;
    }

我想以某种方式将其放入一个流，因为目前我正在多次迭代集合。还是我应该使用循环的情况？

的含义

PS希望是代码自我解释 因为我得到了很多回答，即在一次迭代中不可能做到这一点，所以我正在更新这个问题。我知道不可能在一次迭代中进行操作，但是像这样，我可以用两个迭代来进行：

@Override
    public Map<User, BigDecimal> getCurrentBalanceAlternative(Group group) {
        var currentBalance = new HashMap<User, BigDecimal>();
        final var defaultTotalWeight = BigDecimal.valueOf(group.getDefaultTotalWeight());
        var totalExpense = BigDecimal.ZERO;

        for(Expense expense: group.getExpenses()){
            var expenseUser = expense.getUser();
            var expenseAmount = expense.getAmount();

            totalExpense = totalExpense.add(expenseAmount);

            currentBalance.put(expenseUser, currentBalance.getOrDefault(expenseUser, BigDecimal.ZERO).add(expenseAmount));
        }

        var averageExpensePerUser = totalExpense.divide(defaultTotalWeight);
        currentBalance.entrySet()
                .forEach(e -> e.setValue(e.getValue().subtract(averageExpensePerUser)));

        return currentBalance;
    }

但是，使用流，我必须分别计算totalexpense。