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    <p>This is a bad benchmark IMO.</p> <ul> <li>need to repeat in loop multiple times to warm up jvm</li> <li>need to DO something in your iterative loop or it can be optimized array</li> <li><code>ArrayList</code> resizes, which is costly. If you had constructed <code>ArrayList</code> as <code>new ArrayList(500000)</code> you would construct in one blow, and then all allocations would be quite cheap (one preallocating backed array)</li> <li>You don't specify your memory JVM - it should be run with -xMs == -Xmx (everything preallocated) and sufficiently high that no GC is likely to be triggered</li> <li>This benchmark doesn't cover the most unpleasant aspect of LinkedList - random access. (an iterator isn't necessarily the same thing). If you feed say 10% of the size of a large collection as a random selection of <code>list.get</code> you will find linkedlists are awful for grabbing anything other than the first or last element. </li> </ul> <p>For an arraylist: the jdk get is what you'd expect:</p> <pre><code>public E get(int index) { RangeCheck(index); return elementData[index]; } </code></pre> <p>(basically just return the indexed array element.,</p> <p>For a linkedlist:</p> <pre><code>public E get(int index) { return entry(index).element; } </code></pre> <p>looks similar? Not quite. entry is a method not an primitive array, and look what it has to do:</p> <pre><code>private Entry&lt;E&gt; entry(int index) { if (index &lt; 0 || index &gt;= size) throw new IndexOutOfBoundsException("Index: "+index+ ", Size: "+size); Entry&lt;E&gt; e = header; if (index &lt; (size &gt;&gt; 1)) { for (int i = 0; i &lt;= index; i++) e = e.next; } else { for (int i = size; i &gt; index; i--) e = e.previous; } return e; } </code></pre> <p>That's right, if you ask for say <code>list.get(250000)</code>, it's gotta start at the head and repeatedly iterate through the next element. 250000 accesses or so (there's an optimization in the code where it starts at head or tail depending on which would be less accesses.)</p>
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    1. COAnd yes, when I run a (not so great benchmark, but with these in mind), I get the ArrayList consistently faster as long as I preconstruct the ArrayList. At small numbers the time to build the arraylist structure (empty) starts to have some effect. I'd be glad to share my program, but OTOH I am the first to admit, I am NOT good at writing these JVM benchmarks - they really can be horridly misleading for some of the reasons I mention above.
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    2. COjust as you point out Java as a lot of nondeterministic behavior: JIT compiling, GC, maybe more. Benchmarks have to be taken with a grain of salt but sometimes it's useful to do timing seeing if "method x is faster than method y most of the time"
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    3. COBelieve me I'm not criticizing the intention of the poster. It is GOOD to check assumptions. I merely wanted to point out that benchmarks are very difficult to do correctly in Java, especially given JVM warmup and optimizations.
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