Question

我是Java复杂概念的新手，我也知道这不是一个困难的问题，但是我知道我在做一些错误，这是我班上的一个方法，并且正在我的主要方法中提取其值，但显示NaN 这是方法：

protected static Map<String, Double> getSlaMetrics(List<Vm> vms) {
        Map<String, Double> metrics = new HashMap<String, Double>();
        List<Double> slaViolation = new LinkedList<Double>();
        double totalAllocated = 0;
        double totalRequested = 0;
        double totalUnderAllocatedDueToMigration = 0;

    for (Vm vm : vms) {
        double vmTotalAllocated = 0;
        double vmTotalRequested = 0;
        double vmUnderAllocatedDueToMigration = 0;
        double previousTime = -1;
        double previousAllocated = 0;
        double previousRequested = 0;
        boolean previousIsInMigration = false;

        for (VmStateHistoryEntry entry : vm.getStateHistory()) {
            if (previousTime != -1) {
                double timeDiff = entry.getTime() - previousTime;
                vmTotalAllocated += previousAllocated * timeDiff;
                vmTotalRequested += previousRequested * timeDiff;

                if (previousAllocated < previousRequested) {
                    slaViolation.add((previousRequested - previousAllocated) / previousRequested);
                    if (previousIsInMigration) {
                        vmUnderAllocatedDueToMigration += (previousRequested - previousAllocated)
                                * timeDiff;
                    }
                }
            }

            previousAllocated = entry.getAllocatedMips();
            previousRequested = entry.getRequestedMips();
            previousTime = entry.getTime();
            previousIsInMigration = entry.isInMigration();
        }

        totalAllocated += vmTotalAllocated;
        totalRequested += vmTotalRequested;
        totalUnderAllocatedDueToMigration += vmUnderAllocatedDueToMigration;
    }

    metrics.put("overall", (totalRequested - totalAllocated) / totalRequested);
    if (slaViolation.isEmpty()) {
        metrics.put("average", 0.);
    } else {
        metrics.put("average", MathUtil.mean(slaViolation));
    }
    metrics.put("underallocated_migration", totalUnderAllocatedDueToMigration / totalRequested);
    // metrics.put("sla_time_per_vm_with_migration", slaViolationTimePerVmWithMigration /
    // totalTime);
    // metrics.put("sla_time_per_vm_without_migration", slaViolationTimePerVmWithoutMigration /
    // totalTime);

    return metrics;
}

我正在尝试通过以下代码打印其值：

Map<String, Double> results = getSlaMetrics(vmList);
System.out.println("Overall Violations:" + results.get("overall"));

我知道这是一个基本问题，但是请不要介意。

Answer 1

获得 NaN“不是数字” 表示我们试图将零除以零。将非零数字除以零将得到-Infinity或Infinity。我会看一下这行，并确保不要将数字除以零。

metrics.put（“ overall”，（totalRequested-totalAllocated）/ totalRequested）;

正如Ivan在下面的评论中提到的，让我们演示NaN，-Infinity和Infinity

的几种情况。

System.out.println(0.0/0.0);
System.out.println(0/0.0);
System.out.println(-1/0.0);
System.out.println(1/0.0);

它产生以下输出：

NaN
NaN
-Infinity
Infinity

Answer 2

这里的实际问题不在于Map及其方法，而在于代码。如果您执行此代码，则控件将永远不会转到以下


if (previousTime != -1) {
                double timeDiff = entry.getTime() - previousTime;
                vmTotalAllocated += previousAllocated * timeDiff;
                vmTotalRequested += previousRequested * timeDiff;

                if (previousAllocated < previousRequested) {
                    slaViolation.add((previousRequested - previousAllocated) / previousRequested);
                    if (previousIsInMigration) {
                        vmUnderAllocatedDueToMigration += (previousRequested - previousAllocated)
                                * timeDiff;
                    }
                }

因此在以下分配中分配的值为零

         totalAllocated += vmTotalAllocated;          //  zero
        totalRequested += vmTotalRequested;           // zero
        totalUnderAllocatedDueToMigration += vmUnderAllocatedDueToMigration;  // zero

因此Map中的以下值为0.0 / 0.0，即NaN

 metrics.put("overall", (totalRequested - totalAllocated) / totalRequested); 

   // Value in Map for Key "overall" is ==> 0.0 - 0.0/0.0 = NaN

因此，如果输出中包含NaN，就不足为奇了。

从受保护的方法java获取hashmap值

2 个答案: