private E unlinkFirst ( Node < E > f ) { // assert f == first && f != null; final E element = f . item ; final Node < E > next = f . next ; f . item = null ; f . next = null ; // help GC first = next ; if ( next == null ) last = null ; else next . prev = null ; size -- ; modCount ++ ; return element ; }
Unlinks non - null first node f .