java programming language .. need the explanation please

4. An array-based implementation of the Stack abstract data type has the following method: 1 public Item pop if (isEmpty)) throw new NoSuchElementException("Stack underflow"); Item itema[N1]; 2 4 5 shrink size of array if necessary 6 if (N > 0 &Na.length/4) resize(a.length/2); 7 return item; tle problem which ca show how to prevent this from happening