Streams : Calculate the difference of totals in one go

Question

I have a List<LedgerEntry> ledgerEntries and I need to calculate the sum of creditAmount and debitAmount.

class LedgerEntry{
 private BigDecimal creditAmount;
 private BigDecimal debitAmount;

 //getters and setters
}

I have implemented this as,

BigDecimal creditTotal = ledgeredEntries.stream().map(p ->p.getCreditAmount()).
reduce(BigDecimal.ZERO, BigDecimal::add);
BigDecimal debitTotal = ledgeredEntries.stream().map(p ->p.getDebitAmount()).
reduce(BigDecimal.ZERO, BigDecimal::add);
BigDecimal sumCreditDebit = creditTotal.subtract(debitTotal);

This looks like I'm iterating over the List twice. Is there a way to get this done in one go without having to steam the list twice?

Answer 1

Just reduce it to:

BigDecimal sumCreditDebit = ledgeredEntries.stream().map(p -> p.getCreditAmount()
        .subtract(p.getDebitAmount()))
        .reduce(BigDecimal.ZERO, BigDecimal::add);