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POArrayList Vs LinkedList
 

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    <p>I was following a <a href="https://stackoverflow.com/questions/322715/when-to-use-linkedlist-over-arraylist/322742#322742">previous post</a> on this that says:</p> <blockquote> <p>For LinkedList</p> <ul> <li>get is O(n)</li> <li>add is O(1)</li> <li>remove is O(n)</li> <li>Iterator.remove is O(1)</li> </ul> <p>For ArrayList</p> <ul> <li>get is O(1)</li> <li>add is O(1) amortized, but O(n) worst-case since the array must be resized and copied</li> <li>remove is O(n)</li> </ul> </blockquote> <p>So by looking at this, I concluded that if I've to do just sequential insert in my collection for say 5000000 elements, <code>LinkedList</code> will outclass <code>ArrayList</code>.</p> <p>And if I've to just fetch the elements from collection by iterating i.e. not grabbing the element in middle, still <code>LinkedList</code> will outclass `ArrayList. </p> <p>Now to verify my above two statements, I wrote below sample program… But I'm surprised that my above statements were proven wrong.</p> <p><code>ArrayList</code> outclassed <code>Linkedlist</code> in both the cases. It took less time than <code>LinkedList</code> for adding as well as fetching them from Collection. Is there anything I'm doing wrong, or the initial statements about <code>LinkedList</code> and <code>ArrayList</code> does not hold true for collections of size 5000000?</p> <p>I mentioned size, because if I reduce the number of elements to 50000, <code>LinkedList</code> performs better and initial statements hold true.</p> <pre><code>long nano1 = System.nanoTime(); List&lt;Integer&gt; arr = new ArrayList(); for(int i = 0; i &lt; 5000000; ++i) { arr.add(i); } System.out.println( (System.nanoTime() - nano1) ); for(int j : arr) { ; } System.out.println( (System.nanoTime() - nano1) ); long nano2 = System.nanoTime(); List&lt;Integer&gt; arrL = new LinkedList(); for(int i = 0; i &lt; 5000000; ++i) { arrL.add(i); } System.out.println( (System.nanoTime() - nano2) ); for(int j : arrL) { ; } System.out.println( (System.nanoTime() - nano2) ); </code></pre>
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    1. COfor your LL are you adding to the head or tail?
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    2. COAlso remember you can specify `initialCapacity` for an ArrayList if you know how many elements it needs to hold, which removes the `O(n)` worst case.
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    3. CO@Andrew good point; always a good idea if you have a reasonable lower bound on the array size.
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