Reading double values from a file.

Question

I'm trying to read some numbers (double) from a file and store them in an ArrayList and an array (yes, I need both) with the code below:

try {
 Scanner scan = new Scanner(file).useDelimiter("\\s*\\n");

 while(scan.hasNextDouble())
 {
  tmp.add(scan.nextDouble());
 }

 Double[][] tmp2 = new Double[tmp.size()/2][2];
 int tmp3 = 0;
 for(int i = 0; i < tmp.size()/2; i++)
 {
  for(int j = 0; j < 2; j++)
  {
   tmp2[i][j] = tmp.get(tmp3);
   tmp3++;
  }
 }

} catch (FileNotFoundException e1) {
 e1.printStackTrace();
}

}

The file I'm trying to read is:

0.0 0.0
0.023 0.023
0.05 0.05
0.2 0.2
0.5 0.5
0.8 0.8
0.950 0.950
0.977 0.977
1.0 1.0

But well my code doesn't work, the hasNextDouble() function doesn't find anything, what am I doing wrong?

EDIT: ok so I edited the source a bit (changed from Object[][] to Double[][]) and added inserting values into the array after they were inserted into the ArrayList, but it still doesn't work - the 'while' loop isn't executed a single time.

Answer 1

Try setting the delimiter first:

scan.useDelimiter("\\s+");

JavaDoc

Answer 2

I tried reducing the code down to only test the Scanner by itself. The following code works with your data file:

public static void main(String[] args) {
    Scanner scan;
    File file = new File("resources\\scannertester\\data.txt");
    try {
        scan = new Scanner(file);

        while(scan.hasNextDouble())
        {
            System.out.println( scan.nextDouble() );
        }

    } catch (FileNotFoundException e1) {
            e1.printStackTrace();
    }

}

I got the following (expected) output:

0.0
0.0
0.023
0.023
0.05
0.05
0.2
0.2
0.5
0.5
0.8
0.8
0.95
0.95
0.977
0.977
1.0
1.0

Try this to make sure you're referencing the correct file.

Answer 3

Below is my rendition of your code, adapted to make it run. It immediately explodes with an array indexing exceptions.

So: Can you give us a little more framework? What's different from what I did?

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

public class Zenzen {

   private static ArrayList<Double> tmp = new ArrayList<Double>();

   private static File file = new File("Zenzen.dat");

   public static void main(String[] args) {

      Scanner scan;
      try {
         scan = new Scanner(file);
         Object[][] tmp2 = new Object[tmp.size() / 2][2];
         int tmp3 = 0;

         while (scan.hasNextDouble()) {
            tmp.add(scan.nextDouble());
            System.out.println(Arrays.deepToString(tmp.toArray())); // debug print
            for (int i = 0; i < tmp.size() / 2; i++) {
               for (int j = 0; j < 2; j++) {
                  tmp2[i][j] = tmp.get(tmp3);
                  tmp3++;
               }
            }
         }

      } catch (FileNotFoundException fnfe) {
         fnfe.printStackTrace();
      }
   }
}

---

[0.0]
[0.0, 0.0]
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
    at Zenzen.main(Zenzen.java:26)