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    <p>I think it is an artefact of how you are benchmarking the code.</p> <p>I have run the following benchmark using JVM <code>1.7.0_09</code> with <code>-XX:+AggressiveOpts -XX:CompileThreshold=1</code>:</p> <pre><code>import java.util.ArrayList; import java.util.List; import java.util.Random; public class Main { static final int COUNT = 1000000; static int[] ints = new int[COUNT]; static Integer[] integers = new Integer[COUNT]; static void primitiveToObject() { List&lt;Integer&gt; objects = new ArrayList&lt;Integer&gt;(ints.length); for (int i = 0; i &lt; ints.length; i++) { int value = ints[i] + 1; objects.add(value); //boxing } } static void objectsToPrimitiveToObject() { List&lt;Integer&gt; result= new ArrayList&lt;Integer&gt;(integers.length); for (int i = 0; i &lt; integers.length; i++) { int value = integers[i] + 1; //unboxing result.add(value); //boxing } } public static void main(String[] args) { Random rand = new Random(); for (int i = 0; i &lt; COUNT; ++i) { int val = rand.nextInt(); ints[i] = val; integers[i] = val; } for (int i = 0; i &lt; 10; ++i) { long start_p = System.currentTimeMillis(); for (int j = 0; j &lt; 100; ++j) { primitiveToObject(); } long end_p = System.currentTimeMillis(); long start_o = System.currentTimeMillis(); for (int j = 0; j &lt; 100; ++j) { objectsToPrimitiveToObject(); } long end_o = System.currentTimeMillis(); System.out.printf("p2o:%d o2p2o:%d\n", end_p - start_p, end_o - start_o); } } } </code></pre> <p>The results were as follows:</p> <pre><code>p2o:2043 o2p2o:818 p2o:709 o2p2o:748 p2o:670 o2p2o:756 p2o:675 o2p2o:742 p2o:679 o2p2o:750 p2o:700 o2p2o:757 p2o:738 o2p2o:733 p2o:706 o2p2o:786 p2o:684 o2p2o:752 p2o:676 o2p2o:799 </code></pre> <p>As you can see, after the initial warm-up, <code>primitiveToObject()</code> is faster, as one might expect from a method that's doing less work.</p> <p>For completeness, I've also tested this using JDK 6, and observed similar results.</p>
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    1. COThanks. My mistake was to use single call for every method instead of multiple calling.
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