为什么我的ArrayList为空？

Question

I am working on Project Euler problem 13. ( https://projecteuler.net/problem=13 ) The file "Large_Num_List.txt" is the list provided by the project Euler with each number on its own line with a quote mark at the beginning and end of each line. The statement bial.isEmpty() returns true. Why is this happening? (I suspect because this is my first time using Scanner to read a text file.)

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
import java.util.ArrayList;
import java.math.BigInteger;
import java.util.Iterator;

public class LargeSumTwo
{
  public static void main(String[] args)
  {

    ArrayList<BigInteger> bial = new ArrayList<BigInteger>();
    File file = new File("Large_Num_List.txt");

    try 
    {

        Scanner scan = new Scanner(file);

        while(scan.hasNextBigInteger()) 
        {
            bial.add((BigInteger) scan.nextBigInteger());
        }
        scan.close();
    } 
    catch (FileNotFoundException e) 
    {
        e.printStackTrace();
    }

    System.out.println(bial.isEmpty());
    BigInteger answer = new BigInteger("0");
    Iterator<BigInteger> iter = bial.iterator();

    while(iter.hasNext())
    {
      answer.add(iter.next());
    }

    System.out.println(answer);
  }
}

Answer 1

You need to strip the quotes first. hasNextBigInteger() will only return true if Scanner can parse a BigInteger . The quotes around the numbers will cause hasNextBigInteger() to return false .

JavaDoc: http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#hasNextBigInteger%28%29

Answer 2

Should you add BigInteger in this way:

while(iter.hasNext())
{
  answer = answer.add(iter.next());
}

as BigDecimal numbers are immutable?