Re: [rules-dev] BUG: [5.3.0.Final] CollectSetAccumulateFunction should probably use IdentityHashMap internally
I don't think that this would be a good idea. Consider, for instance,
IdentityHashMap<String,Integer> map =
new IdentityHashMap<String,Integer>();
map.put( "one", 1 );
map.put( new String( "one" ), 2 );
which results in kay and value sets:
keys: [one, one]
values: [2, 1]
"equals" should not be based on mutable properties reflecting state,
just like a body paint job doesn't change the identity of your car -
it just makes the Joneses think so ;-)
-W
On 25/02/2012, SirMungus <Patrick_Rusk(a)ssga.com> wrote:
[First post. I apologize in advance if I'm following the wrong
protocol to
report a bug.]
I had a rule using the collectSet() accumulator that was giving me an NPE at
line 123 of CollectSetAccumulateFunction.java, highlighted below:
public void reverse(Serializable context,
Object value) throws Exception {
CollectListData data = (CollectListData) context;
CollectListData.MutableInt counter = data.map.get( value );
*/if( (--counter.value) == 0 ) {/*
data.map.remove( value );
}
}
When looking in the debugger, I could see that the "value" passed in was
indeed present within the "data.map". However, the
"data.map.get(value)" was
returning null. I thankfully realized this was because the object had
changed, which changed its hashCode(). The stored hashCode() in the HashMap
was different from its current hashCode().
I solved my problem by reimplementing my hashCode() as
System.identityHashCode(this) and my equals as "this == other".
However, I suspect the CollectSetAccumulateFunction should really use an
IdentityHashMap in this situation. It's a really bad idea to allow mutable
objects as keys in HashMap, and there is nothing about the collectSet()
accumulator function that suggests that it should only collect immutable
objects.
Thanks.
P.S. I'm loving Drools. Great tool.
--
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