BufferedReader to BigInteger variable

Question

So I have a very long text file and using Scanner to load it takes about half an hour so I'm trying to switch over to BufferedReader and this is the code I have right now

public static void main(String[] args) {
    // TODO Auto-generated method stub
    BufferedReader Br1 = null;
    BigInteger num = new BigInteger ("0");
    String Line = "";
    try {
        Br1 = new BufferedReader (new FileReader("text.txt"));
        System.out.println("Read line method");
        Line = Br1.readLine();
        while(Line != null) {
            num = num.add(new BigInteger(Line));
            System.out.println(Line);
            Line = Br1.readLine();
        }

        System.out.println("number " + num);
    } catch (IOException ioe) {System.out.println("error");}

}

To test it I made the text file 2 1 0 where all the numbers are on separate lines

I want it to give me a BigInteger 210 but instead it gives me 3, I tried messing around with different ways of adding to the BigInteger but I can't get it to work right. How should I do this?

`add` will add the numbers, so you are basically calculating 2+1+0=3. Why would you want to have 210? — SilverNak, May 14 '17 at 15:33
What else do you expect from, num.add(new BigInteger(Line)); ? — Manish Kumar Sharma, May 14 '17 at 15:34
Well I tried and, shiftLeft, and a couple other things but nothing worked — Samantha Clark, May 14 '17 at 15:38
Why do you want to create a giant BiInteger like that in the first place. My guess is that there is a better way to do what you want to achieve. What do you want to achieve? — JB Nizet, May 14 '17 at 15:42

score 0 · Answer 1 · edited May 14 '17 at 15:38

0

To get 210, first append all characters to String and then convert to BigInteger, as following:

String number;
while(Line != null) {
    //num = num.add(new BigInteger(Line));
    number += Line;
    System.out.println(Line);
    Line = Br1.readLine();
}
num = new BigInteger(number);

edited May 14 '17 at 15:38

dumbPotato21

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answered May 14 '17 at 15:35

Kaushal28

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doesn't make a much of a difference here, but you should prefer `StringBuilder` instead of `String` here, considering `Strings` are immutable, and add overhead to the program. – dumbPotato21 May 14 '17 at 15:41
Thank you, that did the trick :) – Samantha Clark May 14 '17 at 15:42
@SamanthaClark You are Welcome mate! please Consider @Shashwat comment and you can use `StringBuilder`. You can accept the answer if it helped :) – Kaushal28 May 14 '17 at 15:48

dumbPotato21 · Accepted Answer · 2017-05-14T15:45:46.427

0

BigInteger, as the name suggests, is like an Integer. In Integers, 1+2+0 would be 3, and not 120. If that's what you want, do use StringBuilder, like

StringBuilder s = new StringBuilder("");
while(Line != null) {
    s.append(Line);
    Line = Br1.readLine();
}

If you want that as a BigInteger, do

BigInteger num = new BigInteger(s.toString());

edited May 14 '17 at 15:45

answered May 14 '17 at 15:37

dumbPotato21

5,669
5
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But what if OP wants `BigInteger`? – Kaushal28 May 14 '17 at 15:38
2

@Kaushal28 considered. – dumbPotato21 May 14 '17 at 15:39
Now this part of the code doesn't work 'num = new BigInteger(s);' How should I change this? – Samantha Clark May 14 '17 at 15:44
@SamanthaClark : It should work. What's not working? – Manish Kumar Sharma May 14 '17 at 15:47
@SamanthaClark do `num = new BigInteger(s.toString())` The Constructor of `BigInteger` doesn't allow a `CharSequence`, only a `String`. – dumbPotato21 May 14 '17 at 15:47
That fixed it, thank you very much for all your help – Samantha Clark May 14 '17 at 15:52
@SamanthaClark If it helped, you could select the answer by the buttons on the left. – dumbPotato21 May 14 '17 at 15:52
I hit the green arrow, hope that selected your answer. Also it had the unexpected side affect of speeding up my program tremendously! :D – Samantha Clark May 14 '17 at 16:31
Oh, no wonder, I forgot to change it from loading the test example, I thought it was strange lol – Samantha Clark May 14 '17 at 18:17

BufferedReader to BigInteger variable

2 Answers2