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Java Cookbook
book

Java Cookbook

by Ian F. Darwin
June 2001
Intermediate to advanced content levelIntermediate to advanced
888 pages
21h 1m
English
O'Reilly Media, Inc.
Content preview from Java Cookbook

High-Resolution Timers

Problem

You need to time how long something takes.

Solution

Call System.getTimeMillis( ) twice, and subtract the first result from the second result.

Discussion

Needing a timer is such a common thing that, instead of making you depend on some external library, the developers of Java have built it in. The System class contains a static method that returns the current time (since 1970) in milliseconds. Thus, to time some event, use this:

long start = System.getTimeMillis(  ); 
method_to_be_timed(  ); 
long end = System.getTimeMillis(  ); l
ong elapsed = end - start;    // time in msec.

Here is a short example to measure how long it takes a user to press return. We divide the time in milliseconds by a thousand to get seconds, and print it nicely using a NumberFormat:

// Timer0.java 
long t0, t1; 
System.out.println("Press return when ready"); 
t0=System.currentTimeMillis(  ); 
int b; 
do { 
    b = System.in.read(  ); 
} while (b!='\r' && b != '\n');

t1=System.currentTimeMillis(  ); 
double deltaT = t1-t0; 
System.out.println("You took " +  
    DecimalFormat.getInstance(  ).format(deltaT/1000.) + " seconds.");

This longer example uses the same technique, but computes a large number of square roots and writes each one to a discard file using the getDevNull( ) method from Section 2.5:

import java.io.*; import java.text.*; /** * Timer for processing sqrt and I/O operations. */ public class Timer { public static void main(String argv[]) { try { new Timer().run( ); } catch (IOException e) { System.err.println(e); ...
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Publisher Resources

ISBN: 0596001703Supplemental ContentCatalog PageErrata