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PO"Comparison method violates its general contract!" - finding small sample data set
 

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  1. PO"Comparison method violates its general contract!" - finding small sample data set
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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/8327514/comparison-method-violates-its-general-contract">“Comparison method violates its general contract!”</a> </p> </blockquote> <p>I have a larger sample of partially sorted data (> 700 items) which I want to sort with Java 7 and get the following exception:</p> <pre><code>java.lang.IllegalArgumentException: Comparison method violates its general contract! at java.util.TimSort.mergeLo(TimSort.java:747) at java.util.TimSort.mergeAt(TimSort.java:483) at java.util.TimSort.mergeCollapse(TimSort.java:410) at java.util.TimSort.sort(TimSort.java:214) at java.util.TimSort.sort(TimSort.java:173) at java.util.Arrays.sort(Arrays.java:659) at java.util.Collections.sort(Collections.java:217) </code></pre> <p>Now I'm trying to lower the size of the data set to make finding the reason simpler. I've written a small application which picks a random subset out of the larger set to reproduce the exception.</p> <pre><code>private static final int SUBSET_SIZE = 32; public void testSorting() { ... final Random random = new Random(); for (int i = 10000000; i-- &gt; 0; ) { testFew(strings, random); } } private void testFew(List&lt;String&gt; strings, Random random) { final List&lt;String&gt; list = new ArrayList&lt;String&gt;(); int index = 0; for (int i = 0; i &lt; SUBSET_SIZE; i++) { final int rnd = random.nextInt(strings.size() / 100) + 1; index = (index + rnd) % strings.size(); list.add(strings.get(index)); } try { Collections.sort(list, MY_COMPARATOR); } catch (RuntimeException ex) { for (String s : list) { System.err.println(s); } throw ex; } } </code></pre> <p>The strange thing is that finding a sample to reproduce is very simple if the subset contains <strong>at least 32 items</strong>, but I've did not succeeded in finding a smaller set. IMHO, this smells rather like a bug in the sorting algorithm than in our comparator.</p>
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    1. COCan you post your comparator here?
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    2. COI bet $1000 that the bug is in your code, and not in the sort algorithm. Why not post its code for us to inspect it, along with the full stack trace of the exception?
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