Ruiqi Dong created COLLECTIONS-891:
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Summary: IndexedCollection.contains() can return true for objects
that were never added
Key: COLLECTIONS-891
URL: https://issues.apache.org/jira/browse/COLLECTIONS-891
Project: Commons Collections
Issue Type: Bug
Components: Collection
Reporter: Ruiqi Dong
*Summary*
`IndexedCollection` is still a `Collection`, so `contains(x)` should answer
whether an equal object is present in the collection.
The current implementation answers a different question: whether the collection
contains *any* element whose transformed key matches `keyTransformer.apply(x)`.
That produces false positives whenever two different objects map to the same
key.
*Affected code*
File:
`src/main/java/org/apache/commons/collections4/collection/IndexedCollection.java`
{code:java}
@SuppressWarnings("unchecked")
@Override
public boolean contains(final Object object) {
return index.containsKey(keyTransformer.apply((C) object));
} {code}
*Reproducer*
Add the following test to
`src/test/java/org/apache/commons/collections4/collection/IndexedCollectionTest.java`:
{code:java}
@Test
void testContainsUsesObjectEqualityNotOnlyTransformedKey() {
final Collection<String> coll = makeUniqueTestCollection();
coll.add("01");
assertFalse(coll.contains("1"));
} {code}
This uses the existing `IntegerTransformer`, so both `"01"` and `"1"` map to
the same key `1`, but the objects are not equal.
Run:
{code:java}
mvn -q
-Dtest=org.apache.commons.collections4.collection.IndexedCollectionTest#testContainsUsesObjectEqualityNotOnlyTransformedKey
test {code}
*Observed behavior*
{code:java}
expected: <false> but was: <true> {code}
*Expected behavior*
`contains("1")` should be `false`, because only `"01"` was added to the
collection.
The class is a `Collection` decorator, not just a key index. Its `contains`
method must preserve collection membership semantics. Matching on transformed
keys instead of object equality breaks the `Collection.contains` contract
whenever the transformer is not injective.
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