Reading from file double value using Scanner - InputMismatchException?

Question

I tried read from file double values and using Scanner with this aim.

It throws InputMismatchException :

"input.txt"  java.util.InputMismatchException
    at java.util.Scanner.throwFor(Scanner.java:909)
    at java.util.Scanner.next(Scanner.java:1530)
    at java.util.Scanner.nextDouble(Scanner.java:2456)

And I can't understand why this happen?

Code:

public class Largest
{
    public static void main(String[] args)
    throws FileNotFoundException
    {
        String filename = "input.txt"; 
        Scanner in = new Scanner(filename);

        double largest = in.nextDouble();
        while (in.hasNextDouble())
        {
            double input = in.nextDouble();
            if (input > largest)
            {
                largest = input;
            }
        }
        in.close();
        System.out.println("Largest value: " + largest);
    }
}

UPDATE:
I tried change double largest = in.nextDouble(); to double largest = 0;
But it get wrong input:

filename     Actual              Expected
-------------------------------------------------------------
"input.txt"  Largest value: 0.0  Largest value: 1.343239923E9
"input2.txt" Largest value: 0.0  Largest value: 40.1

File content is like this:

How to solve this trouble?

double largest = in.nextDouble(); line causing issue. Input you are getting at this line seems not a double value. — kosa
– kosa, Commented Jul 1, 2013 at 14:52
@Nambari How to circumvent this issue? Itried make double largest = 0. Is't arises exception but input is wrong - largest = 0.0 — catch32
– catch32, Commented Jul 1, 2013 at 14:53
@Ravi Thapliyal It's wrong we can't check largest if this double won't larger then 0. Larger keep being larger all time... — catch32
– catch32, Commented Jul 1, 2013 at 14:58
@nazar_art where is the sample input? copy paste the content of input.txt — ajay.patel
– ajay.patel, Commented Jul 1, 2013 at 15:08

catch32 · Accepted Answer · 2013-07-01 19:04:21Z

1

I found solution - need to create File object and then feed it to scanner class:

String filename = "input.txt"; 
File newFile = new File(filename);
Scanner in = new Scanner(newFile);

answered Jul 1, 2013 at 19:04

catch32

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Comments

Ruchira Gayan Ranaweera · Accepted Answer · 2013-07-01 15:16:16Z

0

Try this

import java.io.File; 
import java.io.FileNotFoundException; 
import java.util.Scanner;

public class MainClass{
public static void main(String[] args)
        throws FileNotFoundException
{
    Scanner in = new Scanner(new File("D:\\input.txt"));
    String largestNum=in.next().trim();
    double largest = Double.parseDouble(largestNum);
    while (in.hasNextDouble())
    {
        String Num=in.next().trim();
        double input = Double.parseDouble(Num);
        if (input > largest)
        {
            largest = input;
        }
    }
    in.close();
    System.out.println("Largest value: " + largest);
} }

edited Jul 1, 2013 at 15:16

answered Jul 1, 2013 at 15:11

Ruchira Gayan Ranaweera

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2 Comments

Ravi K Thapliyal Over a year ago

It's not correct to assume each double is on a separate line; specially, when the OP's code clearly never used a nextLine().

Ruchira Gayan Ranaweera Over a year ago

@RaviThapliyal in that case you can use next();

Ravi K Thapliyal · Accepted Answer · 2013-07-01 15:41:54Z

0

Initialise largest to the first double (after checking the type)

Use the correct delimiter to parse your input (\n = newline)

String filename = "input.txt"; 
Scanner in = new Scanner(filename).useDelimiter("\\n");

double largest;
if (in.hasNextDouble())
    largest = in.nextDouble();

while (in.hasNextDouble())
{
    double input = in.nextDouble();
    if (input > largest)
    {
        largest = input;
    }
}

edited Jul 1, 2013 at 15:41

answered Jul 1, 2013 at 15:02

Ravi K Thapliyal

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4 Comments

catch32 Over a year ago

It doesn't work Actual is - Largest value: 4.9E-324 and Expected is - Largest value: 1.343239923E9 Doesn't work

Ravi K Thapliyal Over a year ago

Can you also post your file contents?

Ravi K Thapliyal Over a year ago

@nazar_art Check my updated answer. You need to parse your file line by line since every input is on a new one.

Stephen C Over a year ago

This answer is incorrect. new Scanner("input.txt") creates a scanner for reading a string, not a file.

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