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POStatic block vs static method - initializing static fields
 

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  1. POStatic block vs static method - initializing static fields
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    <p>Out of curiosity, I measured the performance between static block and static method initializer. First, I implemented the above mentioned methods in two separate java classes, like so: </p> <p>First:</p> <pre><code>class Dummy { static java.util.List&lt;Integer&gt; lista = new java.util.ArrayList&lt;Integer&gt;(); static { for(int i=0; i &lt; 1000000; ++i) { lista.add(new Integer(i)); } } } public class First { public static void main(String[] args) { long st = System.currentTimeMillis(); Dummy d = new Dummy(); long end = System.currentTimeMillis() - st; System.out.println(end); } } </code></pre> <p>Second:</p> <pre><code>class Muddy { static java.util.List&lt;Integer&gt; lista = new java.util.ArrayList&lt;Integer&gt;(); public static void initList() { for(int i=0; i &lt; 1000000; ++i) { lista.add(new Integer(i)); } } } public class Second { public static void main(String[] args) { long st = System.currentTimeMillis(); Muddy.initList(); Muddy m = new Muddy(); long end = System.currentTimeMillis() - st; System.out.println(end); } } </code></pre> <p>Then I executed <a href="http://codepad.org/7plqLRVD" rel="nofollow">this</a> little batch script to measure it 100 times and put the values in a file. <code>batchFile.bat First Second dum.res.txt</code></p> <p>After that, I wrote <a href="http://codepad.org/YmME2Df4" rel="nofollow">this</a> piece of code to calculate mean value and standard deviation of Dummy's and Muddy's measured values. </p> <p>This is the result that I've got: </p> <pre><code>First size: 100 Second size: 100 First Sum: 132 Std. deviation: 13 Second Sum: 112 Std. deviation: 9 </code></pre> <p>And it is similar on my other machines...every time I test it.</p> <p>Now I'm wondering, why is it so? I checked the bytecode and Second.class has one instruction more (call to static initList()) between calls to System.currentTimeMillis(). They both do the same thing, but why is the First one slower? I can't really reason it out just by looking at the bytecode, since this was my first time touching <em>javap</em>; I don't understand bytecode yet. </p>
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    1. COTry reversing First and Second in your call to the batch script and see what the results are :)
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    2. COThe number of instructions has nothing to do with how long those instructions take (telling you to drive across town versus across the country - well, unless you live in Lichenstein or something). Are they the exact same instructions? I rather doubt that. On a side note, I'd be hesitant to use your second version, even if it is faster - it relies on making that `initList()` call, something I'd never count on.
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    3. CO@antlersoft It returns the same results. Already tested it.
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