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Message-ID: <5638E9E6.8010805@spaceroots.org>
Date: Tue, 03 Nov 2015 18:07:50 +0100
From: Luc Maisonobe <luc@spaceroots.org>
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To: dev@commons.apache.org
Subject: Re: [5/6] [math] Fixed findbugs warning.
References: <b171f07ef8e741758b13483af6f05efb@git.apache.org>
 <e30b76104ac64664a90583084e733aaf@git.apache.org>
 <229bd4e8035b36ca0f0ba5d78c090b2d@scarlet.be>
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Le 03/11/2015 15:33, Gilles a écrit :
> On Tue, 03 Nov 2015 11:06:50 -0000, luc@apache.org wrote:
>> Fixed findbugs warning.
>>
>> When defining compareTo, we should also define equals and hashcode.
>>
>>
>> Project: http://git-wip-us.apache.org/repos/asf/commons-math/repo
>> Commit:
>> http://git-wip-us.apache.org/repos/asf/commons-math/commit/04454fc0
>> Tree: http://git-wip-us.apache.org/repos/asf/commons-math/tree/04454fc0
>> Diff: http://git-wip-us.apache.org/repos/asf/commons-math/diff/04454fc0
>>
>> Branch: refs/heads/MATH_3_X
>> Commit: 04454fc0096d5d388e10c5b13024b2a947a4e923
>> Parents: b72d446
>> Author: Luc Maisonobe <luc@apache.org>
>> Authored: Tue Nov 3 11:23:46 2015 +0100
>> Committer: Luc Maisonobe <luc@apache.org>
>> Committed: Tue Nov 3 11:23:46 2015 +0100
>>
>>
>> ----------------------------------------------------------------------
>>  .../commons/math3/ml/neuralnet/MapUtils.java    | 24
>> +++++++++++++++++---
>>  1 file changed, 21 insertions(+), 3 deletions(-)
>>
>> ----------------------------------------------------------------------
>>
>>
>>
>> http://git-wip-us.apache.org/repos/asf/commons-math/blob/04454fc0/src/main/java/org/apache/commons/math3/ml/neuralnet/MapUtils.java
>>
>>
>> ----------------------------------------------------------------------
>> diff --git
>> a/src/main/java/org/apache/commons/math3/ml/neuralnet/MapUtils.java
>> b/src/main/java/org/apache/commons/math3/ml/neuralnet/MapUtils.java
>> index 83036c2..6ef9327 100644
>> --- a/src/main/java/org/apache/commons/math3/ml/neuralnet/MapUtils.java
>> +++ b/src/main/java/org/apache/commons/math3/ml/neuralnet/MapUtils.java
>> @@ -17,14 +17,15 @@
>>
>>  package org.apache.commons.math3.ml.neuralnet;
>>
>> -import java.util.HashMap;
>> +import java.util.ArrayList;
>>  import java.util.Collection;
>>  import java.util.Collections;
>> +import java.util.HashMap;
>>  import java.util.List;
>> -import java.util.ArrayList;
>> +
>> +import org.apache.commons.math3.exception.NoDataException;
>>  import org.apache.commons.math3.ml.distance.DistanceMeasure;
>>  import org.apache.commons.math3.ml.neuralnet.twod.NeuronSquareMesh2D;
>> -import org.apache.commons.math3.exception.NoDataException;
>>  import org.apache.commons.math3.util.Pair;
>>
>>  /**
>> @@ -320,5 +321,22 @@ public class MapUtils {
>>          public int compareTo(PairNeuronDouble other) {
>>              return Double.compare(this.value, other.value);
>>          }
>> +
>> +        /** {@inheritDoc} */
>> +        @Override
>> +        public boolean equals(Object other) {
>> +            if (!(other instanceof PairNeuronDouble)) {
>> +                return false;
>> +            }
>> +            return Double.doubleToRawLongBits(value) ==
>> +                   Double.doubleToRawLongBits(((PairNeuronDouble)
>> other).value);
>> +        }
>> +
>> +        /** {@inheritDoc} */
>> +        @Override
>> +        public int hashCode() {
>> +            return Double.valueOf(value).hashCode();
>> +        }
>> +
>>      }
>>  }
> 
> I think that in general, it is not correct to assume pair equality
> by only taking "value" into account.
> I also think that the default implementation provided the correct
> semantics (for the sole usage of sorting).

Sure, but as the compareTo method did only use value, the equals method
should be consistent with it. Otherwise, you could have compareTo return
0 when equals does not return true for example.

best regards,
Luc

> 
> 
> Regards,
> Gilles
> 
> 
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