Java的8 lambda表達式等同於傳統的

Question

我有一個for聲明在Java 7中，它的做工精細：

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(); 
    } 
} 

我想轉換我的代碼爲Stream &收集的Java 8和返回一個雙值爲。

Answer 1

下面應該工作：

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