FULL PRODUCT VERSION :
java version "1.6.0_01"
Java(TM) SE Runtime Environment (build 1.6.0_01-b06)
Java HotSpot(TM) Client VM (build 1.6.0_01-b06, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
None - is a plain java bug

A DESCRIPTION OF THE PROBLEM :
I think I found a Bug in the IdentityHashMap collection: The removeAll Method removes Object by equality not by there Sytem.identityHashCode. Here is the code from the class: (line 411)

public boolean removeAll(Collection<?> c) {
boolean modified = false;
for (Iterator i = iterator(); i.hasNext(); ) {
if (c.contains(i.next())) {
i.remove();
modified = true;
}
}
return modified;
}

As you can see, the hashMap delegates to c.contains() which can be any collection. IMHO it must be:

@Override
public boolean removeAll(Collection<?> c) {
boolean modified = false;
for (Iterator i = c.iterator(); i.hasNext(); ) {
Object object = i.next();
if (PIdentityHashMap.this.containsKey(object)) {
PIdentityHashMap.this.remove(object);
modified = true;
}
}
return modified;
}

We iterate over the collection and not the entries of the map. Here is a little TestCase:

public void test_show_identityHashMap_Bug() {
List<WrongHashCode> removed = new ArrayList<WrongHashCode>();
removed.add(new WrongHashCode("1"));

IdentityHashMap<WrongHashCode, String> hashMap = new IdentityHashMap<WrongHashCode, String>();
hashMap.put(new WrongHashCode("2"), "");

assertFalse(hashMap.keySet().removeAll(removed));
assertEquals(1, hashMap.size());
}

The class WrongHashCode defines hashCode and equals in the following (wrong (-: ) way:

@Override
public int hashCode() {
return 0;
}

@Override
public boolean equals(Object object) {
return true;
}

I patched the class, so I can work on my software.


REPRODUCIBILITY :
This bug can be reproduced always.