Java - Arrays.sort returns 0

Question

import java.io.*;
import java.util.*;
import java.text.*;

public class aaa {

    public static void main(String args[]) throws IOException {

        Scanner sf = new Scanner(new File("C:\\temp_Name\\DataGym.in.txt"));
        int maxIndx = -1;
        String text[] = new String[1000];
        while (sf.hasNext()) {
            maxIndx++;
            text[maxIndx] = sf.nextLine();
        }

        sf.close();

        double average[] = new double[100];

        for (int j = 0; j <= maxIndx; j++) {
            Scanner sc = new Scanner(text[j]);
            int k = 0;
            while (sc.hasNext()) {
                average[k] = Double.parseDouble(sc.next());
                Arrays.sort(average); //returns 0
                System.out.println(average[k]);
                k++;
            }
        }

    }
}

Without Arrays.sort(average) the program prints out all of the array values normally. However, if I add it in the values are all returned as zero. How do I fix this?

What inside the file?

Yassin Hajaj
– Yassin Hajaj

2016-03-25 22:14:52 +00:00
Commented Mar 25, 2016 at 22:14 — Yassin Hajaj
– Yassin Hajaj, Commented Mar 25, 2016 at 22:14
Arrays.sort doesn't return any value.

Andrew
– Andrew

2016-03-25 22:16:28 +00:00
Commented Mar 25, 2016 at 22:16 — Andrew
– Andrew, Commented Mar 25, 2016 at 22:16
and what will you expect?

Andrew
– Andrew

2016-03-25 22:17:10 +00:00
Commented Mar 25, 2016 at 22:17 — Andrew
– Andrew, Commented Mar 25, 2016 at 22:17

Peter Lawrey · Accepted Answer · 2016-03-25 22:17:32Z

5

This is a lot more complicated than it needs to be, in particular you are sorting the array, every time you set one value in it. This means values you added earlier can be overwritten as you fill up the array.

I suggest you sort the array after all the elements have been added.

Also you know the size the array should be

double average[] = new double[maxIndx+1];

A shorter version might look like

Path path = Paths.get("C:\\temp_Name\\DataGym.in.txt");
double[] nums = Files.lines(path)
                    .mapToDouble(Double.parseDouble)
                    .sorted()
                    .toArray();

answered Mar 25, 2016 at 22:17

Peter Lawrey

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Comments

John Bollinger · Accepted Answer · 2016-03-25 22:23:19Z

It seems unlikely that what you have written is what you actually want. In particular, you leave the zeroth element of array text containing null, and you sort array average each time you set any element. That indeed causes your trouble, because average has 100 elements, and they are all initialized to 0 when the array is instantiated. If you set any one element nonzero and then sort the array, the non-zero element will be moved to the end, leaving a zero in its place.

It's hard to tell what you actually do want, but generally speaking, one would fill the array with all desired values before sorting it, and if one reserves more space than one needs in that array, then one would sort only the elements that are in use.

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