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Is there a sort issue with java7? I am using Collections.sort(list, comparator)
When I switched over to java7, I noticed that the sorting resulted in a different list compared to the result when I was using java6.
Example: List = [d, e, b, a, c, f, g, h]
In java6 Collections.sort(List, comparator) resulted in [a, b, c, d, e, f, g, h]
In java7 Collections.sort(List, comparator) resulted in [b, a, c, d, e, f, g, h]
The first two values in the list have been swapped.
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By default, Collection. sort performs the sorting in ascending order. If we want to sort the elements in reverse order we could use following methods: reverseOrder() : Returns a Comparator that imposes the reverse of natural ordering of elements of the collection.
It works on array input. Collections. sort() can sort objects on both contiguous and discrete memory locations: i.e. it can work on both ArrayList and LinkedList . Collections.
Collections. sort() works for objects Collections like ArrayList, LinkedList, etc. We can use Collections. sort() to sort an array after creating an ArrayList of given array items.
So, in the end, Collections#sort uses Arrays#sort (of object elements) behind the scenes. This implementation uses merge sort or tim sort.
Java 7 switched from Merge sort to Tim sort. It might result in slight changes in order with "broken comparators" (quoting comment in source code of Arrays class):
/**
* Old merge sort implementation can be selected (for
* compatibility with broken comparators) using a system property.
* Cannot be a static boolean in the enclosing class due to
* circular dependencies. To be removed in a future release.
*/
Try running your JVM with:
java -Djava.util.Arrays.useLegacyMergeSort=true
It's not clear what "broken comparator" means, but apparently it can result in different order of elements in sorted arrays.
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