如何使用System.currentTimeMillis（）以秒为单位来测量时间跨度？
如何转换System.currentTimeMillis(); 秒？
long start6=System.currentTimeMillis(); System.out.println(counter.countPrimes(100000000)+" for "+start6);
控制台显示5761455 for 1307816001290 。 我无法读取多less秒。
任何帮助？
long start = System.currentTimeMillis(); counter.countPrimes(1000000); long end = System.currentTimeMillis(); System.out.println("Took : " + ((end - start) / 1000));
UPDATE
更准确的解决scheme是：
final long start = System.nanoTime(); counter.countPrimes(1000000); final long end = System.nanoTime(); System.out.println("Took: " + ((end - start) / 1000000) + "ms);
TimeUnit
使用Java 5及更高版本中内置的TimeUnit 枚举 。
long timeMillis = System.currentTimeMillis(); long timeSeconds = TimeUnit.MILLISECONDS.toSeconds(timeMillis);
像这样：
(int)(milliseconds / 1000)
从你的代码看来，你正在试图测量一个计算花了多长时间（而不是试图找出当前的时间）。
在这种情况下，您需要在计算前后调用currentTimeMillis ，取其差值，并将结果除以1000以将毫秒转换为秒。
我在上次作业中写了下面的代码，它可以帮助你：
// A method that converts the nano-seconds to Seconds-Minutes-Hours form private static String formatTime(long nanoSeconds) { int hours, minutes, remainder, totalSecondsNoFraction; double totalSeconds, seconds; // Calculating hours, minutes and seconds totalSeconds = (double) nanoSeconds / 1000000000.0; String s = Double.toString(totalSeconds); String [] arr = s.split("\\."); totalSecondsNoFraction = Integer.parseInt(arr[0]); hours = totalSecondsNoFraction / 3600; remainder = totalSecondsNoFraction % 3600; minutes = remainder / 60; seconds = remainder % 60; if(arr[1].contains("E")) seconds = Double.parseDouble("." + arr[1]); else seconds += Double.parseDouble("." + arr[1]); // Formatting the string that conatins hours, minutes and seconds StringBuilder result = new StringBuilder("."); String sep = "", nextSep = " and "; if(seconds > 0) { result.insert(0, " seconds").insert(0, seconds); sep = nextSep; nextSep = ", "; } if(minutes > 0) { if(minutes > 1) result.insert(0, sep).insert(0, " minutes").insert(0, minutes); else result.insert(0, sep).insert(0, " minute").insert(0, minutes); sep = nextSep; nextSep = ", "; } if(hours > 0) { if(hours > 1) result.insert(0, sep).insert(0, " hours").insert(0, hours); else result.insert(0, sep).insert(0, " hour").insert(0, hours); } return result.toString(); }
只需将纳秒转换为毫秒。
TimeUnit.SECONDS.convert(start6, TimeUnit.MILLISECONDS);
对于从毫秒到秒的转换，由于1秒= 10 3毫秒：
//here m will be in seconds long m = System.currentTimeMillis()/1000; //here m will be in minutes long m = System.currentTimeMillis()/1000*60;
现在Java 8提供了最简洁的方法来获取当前的Unix时间戳：
Instant.now().getEpochSecond();
// Convert millis to seconds. This can be simplified a bit, // but I left it in this form for clarity. long m = System.currentTimeMillis(); // that's our input int s = Math.max(.18*(Math.toRadians(m)/Math.PI),Math.pow(Math.E, Math.log(m)-Math.log(1000))); System.out.println( "seconds: "+s );
