question: public synchronized boolean addAll ( int index , Collection < ? extends E > c ) { modCount ++ ; if ( index < 0 || index > elementCount ) throw new ArrayIndexOutOfBoundsException ( index ) ; Object [ ] a = c . toArray ( ) ; int numNew = a . length ; ensureCapacityHelper ( elementCount + numNew ) ; int numMoved = elementCount - index ; if ( numMoved > 0 ) System . arraycopy ( elementData , index , elementData , index + numNew , numMoved ) ; System . arraycopy ( a , 0 , elementData , index , numNew ) ; elementCount += numNew ; return numNew != 0 ; }
target:  Inserts all of the elements in the specified Collection into this Vector at the specified position.  Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices).  The new elements will appear in the Vector in the order that they are returned by the specified Collection's iterator.