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https://issues.apache.org/jira/browse/MATH-942?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13598071#comment-13598071
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Piotr Wydrych commented on MATH-942:
------------------------------------
bq. I am a bit reluctant to use Object[] as your patch, though. Are you sure it
would always work? I know type erasure occurs, but with your patch, we mainly
apply it ourselves. Is it safe?
I did some reading, scanning other generics classes code, and testing. It seems
that there are two proper ways to do it:
# return {{Object[]}}, or
# return {{List<T>}}.
I suggest returning {{Object[]}}, like {{ArrayList.toArray()}}. I've attached
an updated patch.
Then, the following code will work:
{code}
public class X {
public static void main(String[] args) {
List<Pair<X, Double>> list = new ArrayList<Pair<X, Double>>();
list.add(new Pair<X, Double>(new X(), new Double(1)));
X[] xarr;
Object[] oarr;
try {
xarr = (X[]) new DiscreteDistribution<X>(list).sample(1);
throw new RuntimeException("Expected ClassCastException");
} catch (ClassCastException e) {
}
oarr = new DiscreteDistribution<X>(list).sample(1);
}
}
{code}
> DiscreteDistribution.sample(int) may throw an exception if first element of
> singletons of sub-class type
> --------------------------------------------------------------------------------------------------------
>
> Key: MATH-942
> URL: https://issues.apache.org/jira/browse/MATH-942
> Project: Commons Math
> Issue Type: Bug
> Reporter: Piotr Wydrych
> Attachments: DiscreteDistribution.java.patch
>
>
> Creating an array with {{Array.newInstance(singletons.get(0).getClass(),
> sampleSize)}} in DiscreteDistribution.sample(int) is risky. An exception will
> be thrown if:
> * {{singleons.get(0)}} is of type T1, an sub-class of T, and
> * {{DiscreteDistribution.sample()}} returns an object which is of type T, but
> not of type T1.
> To reproduce:
> {code}
> List<Pair<Object,Double>> list = new ArrayList<Pair<Object, Double>>();
> list.add(new Pair<Object, Double>(new Object() {}, new Double(0)));
> list.add(new Pair<Object, Double>(new Object() {}, new Double(1)));
> new DiscreteDistribution<Object>(list).sample(1);
> {code}
> Attaching a patch.
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