Java Cookbook-date and Times

6.12 Measuring Elapsed time

--problem

You need to time how long long it takes to do something

--solution

Call System.currenttimemillis () Twice,or system.nanotime (), and subtract the first

Ressult from the second result

--discussion

The System class contains the methods for Times.currenttimemillis () return, the current time (since 1970) in Millise Conds,and Nanotime ()

(New in 1.5) returns the relative time in nanoseconds. To time some event with this:

　

Long Start=system.currenttimemillis ();　　Method_to_be_timed ();　　Long End=system.currenttimemillis ();　　Long elapsed=end-start;//time in milliseconds Or:long start=system.nanotime ();　　Method_to_be_timed ();　　Long End=system.nanotime (); Long Elapsed=end-start;//time in nanoseconds

Here's a short example to measure how long it takes a user to press RETURN.

We divide the time in milliseconds by + to get seconds

and print it nicely using a NumberFormat

Long t0,t1;　　　　System.out.println ("Press Return to Ready");　　T1=system.currenttimemillis (); int b;do{b=system.in.read ();}　　while (b!= ' \ r ' &&b!= ' \ n ');　　T1=system.currrenttimemillis ();　　Double deltat=t1-t0; System.out.println (Decimalformat.getinstance (). Format (deltat/1000.) + "seconds.");

　

Import java.io.*;　　Import java.text.*;  /** * Timer for processing sqrt and I/O operations */public class timercompution{public static void Man (string[]　　　　args) {try{new Timer (). run ();　　}catch (IOException e) {System.err.println (e);} } public void Run () throws ioexception{DataInputStream n=new DataOutputStream (New Bufferedoutputstream (New File　　　　　　OutputStream (Sysdep.getdevnull ()));　　　　　　Long t0,t1;　　　　　　System.out.println ("Java starts at" + (T0=system.currenttimemillis ()));　　　　　　Double k;　　　　　　　　for (int i=0;i<100000;i++) {k=2.1*math.sqrt ((dobule) i);　　　　　　N.writedouble (k);　　　　　} System.out.println ("Java Ends at" + (T1=system.currenttimemillis ()));　　　　　Double deltat=t1-t0; System.out.println ("This run took" + decimalformat.getinstance (). Format (deltat/1000.) + "seconds.");}}

　　

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