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From Sean Qiu <sean.xx....@gmail.com>
Subject Re: [jira] Created: (HARMONY-6076) [eut][classlib][luni] - Arrays.sort(T[] a, Comparator<? super T> c) is not stable
Date Tue, 10 Feb 2009 04:55:06 GMT
Yes, seems this patch is not proper, I've revert the patch at r680223.Thanks
for point it out.
Could you please verify it now?


2009/2/10 Regis <xu.regis@gmail.com>

> Regis Xu (JIRA) wrote:
>
>> [eut][classlib][luni] - Arrays.sort(T[] a, Comparator<? super T> c)  is
>> not stable
>>
>> ----------------------------------------------------------------------------------
>>
>>                 Key: HARMONY-6076
>>                 URL: https://issues.apache.org/jira/browse/HARMONY-6076
>>             Project: Harmony
>>          Issue Type: Bug
>>          Components: Classlib
>>    Affects Versions: 5.0M8
>>            Reporter: Regis Xu
>>             Fix For: 5.0M9
>>
>>
>> spec says "This sort is guaranteed to be stable: equal elements will not
>> be reordered as a result of the sort."
>> but Harmony's implementation is not, which cause eut failure in
>> org.eclipse.jdt.core.tests.compiler.test074 - 1.3
>>
>> see the following test:
>>
>> public class TestArrays {
>>    public static void main(String[] args) {
>>        Element[] array = new Element[11];
>>        array[0] = new Element(122);
>>        array[1] = new Element(146);
>>        array[2] = new Element(178);
>>        array[3] = new Element(208);
>>        array[4] = new Element(117);
>>        array[5] = new Element(146);
>>        array[6] = new Element(173);
>>        array[7] = new Element(203);
>>        array[8] = new Element(56);
>>        array[9] = new Element(82);
>>        array[10] = new Element(96);
>>        for (int i = 0; i < array.length; i++) {
>>            System.out.println("Element value is " + array[i].getValue()
>>                    + " index is " + array[i].getIndex());
>>        }
>>
>>        Arrays.sort(array, new ElementComparator());
>>
>>        for (int i = 0; i < array.length; i++) {
>>            System.out.println("Element value is " + array[i].getValue()
>>                    + " index is " + array[i].getIndex());
>>        }
>>    }
>>
>>    public static class Element {
>>        private int value;
>>
>>        private int index;
>>
>>        public int getIndex() {
>>            return index;
>>        }
>>
>>        private static int count = 0;
>>
>>        public int getValue() {
>>            return value;
>>        }
>>
>>        public void setValue(int value) {
>>            this.value = value;
>>        }
>>
>>        public Element(int value) {
>>            this.value = value;
>>            index = count++;
>>        }
>>    }
>>
>>    public static class ElementComparator implements Comparator {
>>
>>        public int compare(Object arg0, Object arg1) {
>>            return ((Element) arg0).getValue() - ((Element)
>> arg1).getValue();
>>        }
>>
>>    }
>> }
>>
>> notice array[1] and array[5] has the same value, the indexes are 1 and 5
>> corresponding, after a stable sort, element has index 1 should be ahead of
>> element has index 5
>>
>> output of RI:
>>
>> =========before sort=============
>> Element value is 122 index is 0
>> Element value is 146 index is 1
>> Element value is 178 index is 2
>> Element value is 208 index is 3
>> Element value is 117 index is 4
>> Element value is 146 index is 5
>> Element value is 173 index is 6
>> Element value is 203 index is 7
>> Element value is 56 index is 8
>> Element value is 82 index is 9
>> Element value is 96 index is 10
>>
>> =========after sort=============
>> Element value is 56 index is 8
>> Element value is 82 index is 9
>> Element value is 96 index is 10
>> Element value is 117 index is 4
>> Element value is 122 index is 0
>> Element value is 146 index is 1
>> Element value is 146 index is 5
>> Element value is 173 index is 6
>> Element value is 178 index is 2
>> Element value is 203 index is 7
>> Element value is 208 index is 3
>>
>> output of Harmony:
>>
>> =========before sort=============
>> Element value is 122 index is 0
>> Element value is 146 index is 1
>> Element value is 178 index is 2
>> Element value is 208 index is 3
>> Element value is 117 index is 4
>> Element value is 146 index is 5
>> Element value is 173 index is 6
>> Element value is 203 index is 7
>> Element value is 56 index is 8
>> Element value is 82 index is 9
>> Element value is 96 index is 10
>>
>> =========after sort=============
>> Element value is 56 index is 8
>> Element value is 82 index is 9
>> Element value is 96 index is 10
>> Element value is 117 index is 4
>> Element value is 122 index is 0
>> Element value is 146 index is 5
>> Element value is 146 index is 1
>> Element value is 173 index is 6
>> Element value is 178 index is 2
>> Element value is 203 index is 7
>> Element value is 208 index is 3
>>
>> notice that in Harmony index 1 and 5 is out of order after sort
>>
>>  Hi,
>
> when I fixed this issue with the following patch:
> Index: modules/luni/src/main/java/java/util/Arrays.java
>
> =====================================================================
>
> --- modules/luni/src/main/java/java/util/Arrays.java
>
> +++ modules/luni/src/main/java/java/util/Arrays.java
>
> @@ -2520,7 +2520,7 @@ public class Arrays {
>
>             Object fromVal = in[start];
>
>             Object rVal = in[r];
>
>             if (c.compare(fromVal, rVal) <= 0) {
>
> -                int l_1 = find(in, rVal, 0, start + 1, med - 1, c);
>
> +                int l_1 = find(in, rVal, -1, start + 1, med - 1, c);
>
>                 int toCopy = l_1 - start + 1;
>
>                 System.arraycopy(in, start, out, i, toCopy);
>
>                 i += toCopy;
>
> I found it made the test
> ArraysTest.test_sort$Ljava_lang_ObjectLjava_util_Comparator faild:
> junit.framework.AssertionFailedError: expected:<200> but was:<310>
>        at junit.framework.Assert.fail(Assert.java:47)
>        at junit.framework.Assert.failNotEquals(Assert.java:277)
>        at junit.framework.Assert.assertEquals(Assert.java:64)
>        at junit.framework.Assert.assertEquals(Assert.java:71)
>        at
> org.apache.harmony.luni.tests.java.util.ArraysTest.test_sort$Ljava_lang_ObjectLjava_util_Comparator(ArraysTest.java:1354)
>
> look into the source, the test use the Comparator for sort:
>        Comparator comparator = new Comparator(){
>            public int compare(Object o1, Object o2) {
>                Integer e1 = (Integer)o1;
>                Integer e2 = (Integer)o2;
>                return e1 > e2 ? 1 : 0;
>            }
>        };
>
> which doesn't impose a total ordering. The order under this Comparator
> can't be defined. So the sort result is depend on implementations.
>
> I suggest remove this test, I believe it's abuse of Comparator.
> What you do think?
>
> --
> Best Regards,
> Regis.
>



-- 
Best Regards
Sean, Xiao Xia Qiu

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