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<a href="http://www.bruceeckel.com/javabook.html">Bruce Eckel's Thinking in Java</a>
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<H2 ALIGN=LEFT>
Locating
the bottleneck
</H2>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Three
approaches to locating the performance-critical part of a program are:
</FONT><a name="_Toc408018852"></a><P></DIV>
<A NAME="Heading637"></A><H3 ALIGN=LEFT>
1.
Install your own instrumentation
</H3>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">&#8220;Profile&#8221;
code by inserting explicit timing: 
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#0000ff">long</font> start = System.currentTimeMillis();
   <font color="#009900">// Operation to be timed goes here</font>
<font color="#0000ff">long</font> time = System.currentTimeMillis() - start; </PRE></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Have
an infrequently-used method print cumulative times out to the console window
with 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>System.out.println(&#160;).</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
Since the compiler will ignore it when false, a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>static
final boolean
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
switch can turn the timing on and off so the code can efficiently be left in
place in released code, ready for emergency use at any time. Even when more
sophisticated profiling is available, this is a convenient way to time a
specific task or operation.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>System.currentTimeMillis(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
returns time in 1/1000ths of a second. However, some systems with time
resolution less than a millisecond (such as a Windows PC) need to repeat an
operation 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>n</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
times and divide the total time by 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>n</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
to get accurate estimates. 
</FONT><a name="_Toc408018853"></a><P></DIV>
<A NAME="Heading638"></A><H3 ALIGN=LEFT>
2.
JDK profiling [2]
<P><A NAME="Index3137"></A></H3>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
JDK comes with a built-in profiler that keeps track of the time spent in each
routine and writes the information to a file. Unfortunately, the JDK profilers
have uneven performance. JDK 1.1.1 works, but subsequent releases have had
various instabilities.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">To
run the profiler, use the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>-prof
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">option
when invoking the unoptimized versions of the Java interpreter, for example: 
</FONT><P></DIV><DIV ALIGN=LEFT><TT><FONT FACE="Courier New" SIZE=3 COLOR="Black">java_g
-prof myClass
</FONT></TT><P></DIV><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Or
with an applet: 
</FONT><P></DIV><DIV ALIGN=LEFT><TT><FONT FACE="Courier New" SIZE=3 COLOR="Black">java_g
-prof sun.applet.AppletViewer applet.html
</FONT></TT><P></DIV><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
profiler output is not particularly easy to decipher. In fact, in JDK 1.0 it
truncates the method names to 30 characters, so it might not be possible to
distinguish between some methods. However, if your platform does support the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>-prof</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
option, either Vladimir Bulatov&#8217;s 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>HyperProf
</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">[3]
or Greg White&#8217;s 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>ProfileViewer</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
[4] will help interpret the results.
</FONT><a name="_Toc408018854"></a><P></DIV>
<A NAME="Heading639"></A><H3 ALIGN=LEFT>
3.
Special tools
</H3>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
best way to keep up with the exploding field of performance optimization tools
is through a Web site such as Jonathan Hardwick&#8217;s 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>Tools
for Optimizing
</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>Java
</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">[5]
at 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>http://www.cs.cmu.edu/~jch/java/tools.html</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.</FONT><a name="_Toc408018855"></a><P></DIV>
<A NAME="Heading640"></A><H3 ALIGN=LEFT>
Tips
for measuring performance
</H3>
<UL>
<LI><FONT FACE="Symbol" SIZE=3 COLOR="Black">	</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Since
profiling uses clock time, make every effort to remove other processes during
the measurement.
</FONT><LI><FONT FACE="Symbol" SIZE=3 COLOR="Black">	</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Always
time the code before and after making changes to verify that, at least on the
test platform, your changes improved the program. (Jon Bentley mentioned that
some of his most logical changes actually slowed the program down.)
</FONT><LI><FONT FACE="Symbol" SIZE=3 COLOR="Black">	</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Try
to make each timing test under identical conditions. 
</FONT><LI><FONT FACE="Symbol" SIZE=3 COLOR="Black">	</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">If
possible, contrive a test that doesn&#8217;t rely on any user input to avoid
variations in user response that can cause the results to fluctuate. 
</FONT><a name="_Toc408018856"></a></UL>
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