流:一次计算总数的差异

Question

我有一个List<LedgerEntry> ledgerEntries,我需要计算creditAmount和debitAmount的总和.

class LedgerEntry{
 private BigDecimal creditAmount;
 private BigDecimal debitAmount;

 //getters and setters
}

我实现了这个,

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);

这看起来像是在迭代List两次.有没有办法一次性完成这项工作,而无需两次蒸发列表？

Answer 1

只需将其减少为:

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

Answer 2

您可以减去其中的各个金额map，然后sum使用reduce

ledgerEntries.stream()
    .map(e->e.getCreditAmount().subtract(e.getDebitAmount())
    .reduce(0,BigDecimal::add);