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copied!<p>An optimization trick that makes your code easier to maintain and less susceptible to a concurrency bug.</p> <pre><code>public class Slow { /** Loop counter; initialized to 0. */ private long i; public static void main( String args[] ) { Slow slow = new Slow(); slow.run(); } private void run() { while( i++ < 10000000000L ) ; } } </code></pre> <p>$ time java Slow<br /> real 0m15.397s<br /> $ time java Slow<br /> real 0m20.012s<br /> $ time java Slow<br /> real 0m18.645s<br /></p> <p><strong>Average: 18.018s</strong></p> <pre><code>public class Fast { /** Loop counter; initialized to 0. */ private long i; public static void main( String args[] ) { Fast fast = new Fast(); fast.run(); } private void run() { long i = getI(); while( i++ < 10000000000L ) ; setI( i ); } private long setI( long i ) { this.i = i; } private long getI() { return this.i; } } </code></pre> <p>$ time java Fast<br /> real 0m12.003s<br /> $ time java Fast<br /> real 0m9.840s<br /> $ time java Fast<br /> real 0m9.686s<br /></p> <p><strong>Average: 10.509s</strong></p> <p>It requires more bytecodes to reference a class-scope variable than a method-scope variable. The addition of a method call prior to the critical loop adds little overhead (and the call might be inlined by the compiler anyway).</p> <p>Another advantage to this technique (always using accessors) is that it eliminates a potential bug in the <strong>Slow</strong> class. If a second thread were to continually reset the value of <strong>i</strong> to 0 (by calling <code>slow.setI( 0 )</code>, for example), the <strong>Slow</strong> class could never end its loop. Calling the accessor and using a local variable eliminates that possibility.</p> <p>Tested using J2SE 1.6.0_13 on Linux 2.6.27-14.</p>

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