(1)如何精确给代码计时;
(2)计时机制本身的时间开销;
经典的程序计时利用Java API方法:System.currentTimeMillis(),在待测代码前后放置一个秒表(stopwatch),计算前后时间差即可。
下面是一个引自“”的stopwatch类,
import java.io.PrintStream;
final class Timer{
private long startTime;
private long endTime;
public Timer() { reset(); }
public void start() {
System.gc();
startTime = System.currentTimeMillis();
}
public void end() {
System.gc();
endTime = System.currentTimeMillis();
}
public long duration() {
return (endTime - startTime);
}
public void printDuration( PrintStream out ) {
long elapsedTimeInSecond = duration() / 1000;
long remainderInMillis = duration() % 1000;
out.println("\nTotal execution time:"
+ elapsedTimeInSecond + "."
+ remainderInMillis
+ " seconds");
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