Java Stream 計算總和 Stream聚合函數對數據求和、最大、最小、平均

BigDecimal total = tOrderOrders.stream() .map(TOrderOrder::getAmount).reduce(BigDecimal.ZERO,BigDecimal::add);

list.stream().mapToDouble(User::getHeight).sum()//和
list.stream().mapToDouble(User::getHeight).max()//最大
list.stream().mapToDouble(User::getHeight).min()//最小
list.stream().mapToDouble(User::getHeight).average()//平均值