Summation program with file read & write snippet

Summation.java

class Summation {
 public static void main(String[] args) throws IOException {
  // Read & write data from file.
  Scanner in = new Scanner(System.in);
  final String fileName = System.getenv("OUTPUT_PATH");
  BufferedWriter bw = new BufferedWriter(new FileWriter(fileName));
  int res;

  int _numbers_size = 0;
  _numbers_size = Integer.parseInt( in .nextLine().trim());
  int[] _numbers = new int[_numbers_size];
  int _numbers_item;
  for (int _numbers_i = 0; _numbers_i < _numbers_size; _numbers_i++) {
   _numbers_item = Integer.parseInt( in .nextLine().trim());
   _numbers[_numbers_i] = _numbers_item;
  }

  res = summation(_numbers);
  bw.write(String.valueOf(res));
  bw.newLine();

  bw.close();
 }

 static int summation(int[] numbers) {
  int sum = 0;
  if (numbers.length > 0) {
   for (int n: numbers) {
    sum += n;
   }

  }
  return sum;
 }
}