Dipanjan Laha created COLLECTIONS-531:
-----------------------------------------
Summary: Generic Wildcards specified in
CollectionUtils#isEqualCollection(Collection, Collection, Equator) may cause
ClassCastException in certain cases
Key: COLLECTIONS-531
URL: https://issues.apache.org/jira/browse/COLLECTIONS-531
Project: Commons Collections
Issue Type: Bug
Components: Collection
Affects Versions: 4.0
Reporter: Dipanjan Laha
Priority: Minor
Attachments: IsEqualCollectionTest.java
CollectionUtils#isEqualCollection(Collection, Collection, Equator) is defined as
{code}
public static boolean isEqualCollection(final Collection<?> a, final
Collection<?> b, final Equator<?> equator) {
...
}
{code}
This makes it possible to invoke it with a code like
{code}
public static class IntegerEquator implements Equator<Integer> {
public boolean equate(Integer o1, Integer o2) {
return o1.intValue() == o2.intValue();
}
public int hash(Integer o) {
return o.intValue();
}
}
@Test
public void test() {
List<Long> longList = Arrays.asList(1L, 2L);
List<Integer> intList = Arrays.asList(1, 2);
assertTrue(CollectionUtils.isEqualCollection(longList, intList, new
IntegerEquator()));
}
{code}
which compiles perfectly but throws a ClassCastException as Long cannot be cast
to an Integer. However, the generics should be defined such that this is
stopped at compile time itself.
If we modify the method to something like
{code}
public static <E> boolean isEqualCollection(final Collection<? extends E> a,
final Collection<? extends E> b, final Equator<? super E> equator) {
...
}
{code}
the above example would give a compile time error. imho we should modify this
method with bounded wildcards. I don't think this change would break any
existing binaries if the method is being used correctly, otherwise it is
probably throwing ClassCastExceptions anyway.
Test case attached
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