Reading from file double value using Scanner - Inp

问题:

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:

89343455
46746846
56.78
55486411

How to solve this trouble?

回答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);

回答2:

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);
} }

回答3:

• 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;
      }
  }