Sort Numeric

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class SortNumeric {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    List<Integer> pool = new ArrayList<Integer>();
    while (true) {
      System.out.print("? ");
      int a = new Integer(in.nextLine());
      if (a == -1) break;
      if (a < 0) continue;
      pool.add(a);
    }
    in.close();
    Collections.sort(pool);
    System.out.println(pool);
  }
}