Question

在阅读Android developers blog post on location时，我偶然发现了这段代码（来自博客的剪切和粘贴）：

List<String> matchingProviders = locationManager.getAllProviders();
for (String provider: matchingProviders) {
  Location location = locationManager.getLastKnownLocation(provider);
  if (location != null) {
    float accuracy = location.getAccuracy();
    long time = location.getTime();

    if ((time > minTime && accuracy < bestAccuracy)) {
      bestResult = location;
      bestAccuracy = accuracy;
      bestTime = time;
    }
    else if (time < minTime && 
         bestAccuracy == Float.MAX_VALUE && time > bestTime){
      bestResult = location;
      bestTime = time;
    }
  }
}

虽然其余部分非常明确，但这条线让我感到难过：

    else if (time < minTime && 
         bestAccuracy == Float.MAX_VALUE && time > bestTime){

'时间'必须在可接受的延迟期内＆amp;比之前的bestTime更新。那讲得通。

但bestAccuracy与Max Float值的比较是什么意思？什么时候精度可以精确地等于浮点数可以容纳的最大值？

Answer 1

如果您按照指向整个源文件的链接，那个特定的位会更有意义。这是一个稍微大一点的片段：

Location bestResult = null;
float bestAccuracy = Float.MAX_VALUE;
long bestTime = Long.MIN_VALUE;

// Iterate through all the providers on the system, keeping
// note of the most accurate result within the acceptable time limit.
// If no result is found within maxTime, return the newest Location.
List<String> matchingProviders = locationManager.getAllProviders();
for (String provider: matchingProviders) {
  Location location = locationManager.getLastKnownLocation(provider);
  if (location != null) {
    float accuracy = location.getAccuracy();
    long time = location.getTime();

    if ((time > minTime && accuracy < bestAccuracy)) {
      bestResult = location;
      bestAccuracy = accuracy;
      bestTime = time;
    }
    else if (time < minTime && bestAccuracy == Float.MAX_VALUE && time > bestTime) {
      bestResult = location;
      bestTime = time;
    }
  }
}

很简单，Float.MAX_VALUE是bestAccuracy的默认值，他只是检查他是否在之前的if子句中没有减少它。

Answer 2

我猜测bestAccuracy已初始化为Float.MAX_VALUE。如果是这样，代码可以概括为：找到具有最小（最佳？）精度且时间大于minTime的提供者。如果没有时间大于minTime，那么只需选择时间最接近minTime的那个。

这可以从

重构

    if ((time < minTime && accuracy < bestAccuracy)) {
      bestResult = location;
      bestAccuracy = accuracy;
      bestTime = time;
    }
    else if (time > minTime && bestAccuracy == Float.MAX_VALUE && time < bestTime) {
      bestResult = location;
      bestTime = time;
    }

到

    if ((time < minTime && accuracy < bestAccuracy)) {
      bestResult = location;
      bestAccuracy = accuracy;
      bestTime = time;
      foundWithinTimeLimit = true;
    }
    else if (time > minTime && !foundWithinTimeLimit && time < bestTime) {
      bestResult = location;
      bestTime = time;
    }

让它更清晰一点。

将精度与Float.MAX_VALUE进行比较意味着什么？

2 个答案: