Java-8 lambda 表达式等价于传统 for

Question

我在 Java 7 中有一个 for 语句，它工作正常：

Double totalDistributedCredit = 0D;
Set<DistributionPlan> distributionPlanList = loadByEntityId(creditResourceId).getDistributionPlan();
for (DistributionPlan distributionPlan : distributionPlanList) {
    Set<DistributedCredit> distributedCreditList = iDistributionPlanService.loadByEntityId(distributionPlan.getId()).getDistributedCredit();
    for (DistributedCredit distributedCredit : distributedCreditList) {
        totalDistributedCredit += distributedCredit.getDistributedAmount();
    }
}

我想在 Java 8 中将我的代码转换为 Stream & collect 并返回一个双精度值。

Answer 1

以下应该可以工作：

double sum = distributionPlanList.stream()
    .flatMap(e -> iDistributionPlanService.loadByEntityId(e.getId()).getDistributedCredit().stream())
    .map(dc -> dc.getDistributedAmount())
    .mapToDouble(Double::doubleValue)
    .sum();