The original failed test case created by FailureDoc is as follow. We have an assertion failure at line 20.

The comments at line 5, 7, 13, and 16 are FailureDoc's explanation. We use the explanation at line 7 and 13 to create two passed test cases (at line 5 the explanation does not give the initial value, at line 16 using ListShortList as type for var11 gives compilation error so we can not use them). These two passed test cases and the original failed test case are Ziyuan's input.

Result from Ziyuan:

-1.0*list._size >= 0.0 (org.apache.commons.collections.primitives.adapters.CharListList:92)

Explanation for the bug:

When checking equality, ShortList object uses an iterator. However, this iterator is wrapped by a Character iterator. When casting from Character to Number, the ClassCastException occurs.

One possible solution is reimplementing the iterator.

In this case, the explanation from Ziyuan is correct. If the size is less than or equals to zero, we have an empty list. Therefore, we do not need to call iterator and the exception does not occur.

The result of Daikon in this case can be found here. In the entry of method wrap() in class CharListList, there is an invariant list.getClass().getName() == org.apache.commons.collections.primitives.ArrayCharList.class. It seems that this invariant is related to casting problem and can be used to understand the bug. However, note that besides this invariant, Daikon returns many other invariants, not only in method wrap() but also in other methods.