blocks|key|1706394|text|java.lang.System.currentTimeMillis()或java.lang.System.nanoTime()应该用来测量运行时间。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1706395|entityMap^0|0|10|11|R|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

<code>java.lang.System.currentTimeMillis()</code> or <code>java.lang.System.nanoTime()</code> ought to work to measure elapsed time.

blocks|key|1706414|text|这是一些示例代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1706415|long+startTime+=+System.currentTimeMillis();
//+Run+some+code;
long+stopTime+=+System.currentTimeMillis();

System.out.println("Elapsed+time+was+"+%2B+(stopTime+-+startTime)+%2B+"+miliseconds.");|code-block|syntax|javascript|1706416|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is some sample code. 

<pre><code>long startTime = System.currentTimeMillis();
// Run some code;
long stopTime = System.currentTimeMillis();

System.out.println("Elapsed time was " + (stopTime - startTime) + " miliseconds.");
</code></pre>

blocks|key|1706449|text|Apache+Commons-Lang还提供了适合您的用途的StopWatch类。它使用System.currentTimeMillis()，因此您仍然会遇到分辨率问题，但您可以暂停并执行圈速等操作。我现在使用它作为事件统计的标准。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1706450|http://commons.apache.org/lang/api-release/org/apache/commons/lang/time/StopWatch.html|offset|length|1706451|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|2E|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

Apache Commons-Lang also has the StopWatch class suited just for your purpose. It uses System.currentTimeMillis(), so you'll still have resolution problems, but you can pause and do lap times and such. I use it as standard now for event stats.

<a href="http://commons.apache.org/lang/api-release/org/apache/commons/lang/time/StopWatch.html" rel="noreferrer">http://commons.apache.org/lang/api-release/org/apache/commons/lang/time/StopWatch.html</a>

blocks|key|1491426|text|我会避免使用System.currentTimeMillis()来测量运行时间。currentTimeMillis()返回“挂钟”时间，该时间可能会发生变化(例如:夏令时、管理员用户更改时钟)，并会扭曲您的时间间隔测量。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1491427|另一方面，System.nanoTime()返回自‘某个参考点’(例如，JVM启动)以来的纳秒数，因此不会受到系统时钟变化的影响。|1491428|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/8/docs/api/java/lang/System.html#currentTimeMillis--|1|2|https://docs.oracle.com/javase/8/docs/api/java/lang/System.html#nanoTime--^0|6|Q|14|J|6|Q|0|14|J|1|0|5|H|5|H|2|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]|$9|10|A|11|1|12]]|E|$]]|$1|F|3|G|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@$9|16|A|17|1|18]]|E|$]]|$1|H|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]|P|$5|K|L|M|E|$N|O]]|Q|$5|K|L|M|E|$N|R]]]]

I would avoid using <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/System.html#currentTimeMillis--" rel="noreferrer"><code>System.currentTimeMillis()</code></a> for measuring elapsed time. <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/System.html#currentTimeMillis--" rel="noreferrer"><code>currentTimeMillis()</code></a> returns the 'wall-clock' time, which may change (eg: daylight savings, admin user changing the clock) and skew your interval measurements. 

<a href="https://docs.oracle.com/javase/8/docs/api/java/lang/System.html#nanoTime--" rel="noreferrer"><code>System.nanoTime()</code></a>, on the other hand, returns the number of nanoseconds since 'some reference point' (eg, JVM start up), and would therefore not be susceptible to system clock changes.

blocks|key|1706556|text|这是我使用System.nanoTime()编写的一个小StopWatch类，正如利的答案中所建议的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1706557|public+class+StopWatch+{
++++//+Constructor
++++public+StopWatch()+{
++++}

++++//+Public+API
++++public+void+start()+{
++++++++if+(!_isRunning)+{
++++++++++++_startTime+=+System.nanoTime();
++++++++++++_isRunning+=+true;
++++++++}
++++}

++++public+void+stop()+{
++++++++if+(_isRunning)+{
++++++++++++_elapsedTime+%2B=+System.nanoTime()+-+_startTime;
++++++++++++_isRunning+=+false;
++++++++}
++++}

++++public+void+reset()+{
++++++++_elapsedTime+=+0;
++++++++if+(_isRunning)+{
++++++++++++_startTime+=+System.nanoTime();
++++++++}
++++}

++++public+boolean+isRunning()+{
++++++++return+_isRunning;
++++}

++++public+long+getElapsedTimeNanos()+{
++++++++if+(_isRunning)+{
++++++++++++return+System.nanoTime()+-+_startTime;
++++++++}
++++++++return+_elapsedTime;
++++}

++++public+long+getElapsedTimeMillis()+{
++++++++return+getElapsedTimeNanos()+/+1000000L;
++++}

++++//+Private+Members
++++private+boolean+_isRunning+=+false;
++++private+long+_startTime+=+0;
++++private+long+_elapsedTime+=+0;
}|code-block|syntax|javascript|1706558|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here is a small StopWatch class I wrote using the System.nanoTime() as suggested in the answer from Leigh:

<pre><code>public class StopWatch {
 // Constructor
 public StopWatch() {
 }

 // Public API
 public void start() {
 if (!_isRunning) {
 _startTime = System.nanoTime();
 _isRunning = true;
 }
 }

 public void stop() {
 if (_isRunning) {
 _elapsedTime += System.nanoTime() - _startTime;
 _isRunning = false;
 }
 }

 public void reset() {
 _elapsedTime = 0;
 if (_isRunning) {
 _startTime = System.nanoTime();
 }
 }

 public boolean isRunning() {
 return _isRunning;
 }

 public long getElapsedTimeNanos() {
 if (_isRunning) {
 return System.nanoTime() - _startTime;
 }
 return _elapsedTime;
 }

 public long getElapsedTimeMillis() {
 return getElapsedTimeNanos() / 1000000L;
 }

 // Private Members
 private boolean _isRunning = false;
 private long _startTime = 0;
 private long _elapsedTime = 0;
}
</code></pre>

What's a simple/easy way to access the system clock using Java, so that I can calculate the elapsed time of an event?

How do I calculate the elapsed time of an event in java?

Java

使用Java访问系统时钟的简单方法是什么，这样我就可以计算事件的运行时间？

问如何在java中计算事件的运行时间？
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