question: public boolean addAll ( Collection < ? extends E > c ) { hashCodeUpToDate = false ; Object [ ] a = c . toArray ( ) ; int numNew = a . length ; ensureCapacityInternal ( size + numNew ) ; System . arraycopy ( a , 0 , elementData , size , numNew ) ; size += numNew ; return numNew != 0 ; }
target:  Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's Iterator. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this list, and this list is nonempty.)