index
Returns the index in this queue of the first occurrence of the specified element, or -1 if the queue does not contain this element. More formally, returns the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.
Return
The index (zero based) of the element or -1 if not found.
Parameters
q
The object to be found