// Pushes an item to the top of the stack.        //         /// <include file='doc\Stack.uex' path='docs/doc[@for="Stack.Push"]/*' />        public void Push(T item) {            if (_size == _array.Length) {                T[] newArray = new T[(_array.Length == 0) ? _defaultCapacity : 2*_array.Length];                Array.Copy(_array, 0, newArray, 0, _size);                _array = newArray;            }            _array[_size++] = item;            _version++;        }
스택이 가득찼는데 Push할때 말고는 메모리할당 없음