Java reading different arrays in text file

Question

I have to read a text file in Java, separate its content into separate arrays, and then compute the average of certain arrays. My problem is that when I try to display a certain array to make sure it works, I get "null" instead of the whole list. Can anyone help me find where I went wrong?

import java.io.*;

class ReadFile {
    public static void main(String args[]) 
        String[] id = new String[1234]; // random number just for initialization
        String[] name = new String[1234];
        String[] asg1 = new String[1234];
        String[] asg2 = new String[1234];

        try {
            String sCurrentLine;
            FileReader fr = new FileReader("Information.txt");
            BufferedReader textReader = new BufferedReader(fr);

            int i;
            String[] array = null;

            // Read file in separate parts and remove commas
            while ((sCurrentLine = textReader.readLine()) != null) {
                array = sCurrentLine.split(",");
                System.out.print(array[0]);
                System.out.print(array[1]);
                System.out.print(array[2]);
                System.out.println(array[3]);
            }

            // enter variables from each line in separate arrays
            for (i = 0; i < array.length; i++) {
                id[i] = array[0];
                name[i] = array[1];
                asg1[i] = array[2];
                asg2[i] = array[3];
            }

            System.out.println(name[i]);
            // "null" appears instead of all the names

            textReader.close();
        } catch (Exception e) {
            // Catch exception if any
            System.err.println("Error: " + e.getMessage());
        }
    }
}

The input looks like this:

ID, name, Asg1, Asg2
123456, Max, 98.00, 80.00
012345, James, 40.00, 69.00
234567, Mary, 78.00, 88.00

Bhushan · Accepted Answer · 2014-01-11 09:01:29Z

3

Reason your code is giving you null is because value of i is array.length at following line.

System.out.println(name[i]);

Consider following example:

int i;
for(i=0;i<5;i++)
{
    System.out.println(i);
}
System.out.println("value of i outside loop: "+i);

Output:

0
1
2
3
4
value of i outside loop: 5

So you are trying to get value at index 5 which is null.

To get the output you want using your current approach you can use following code:

for (i = 0; i < array.length; i++)
{
    System.out.println(id[i] +":"+ name[i] +":"+ asg1[i] +":"+asg2[i]);
}

[Note: if your array size is not fix then you can use ArrayList to store data, which has dynamic (grow-able) arraysize.]

edited Jan 11, 2014 at 9:01

answered Jan 11, 2014 at 8:41

Bhushan

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Comments

Dennis Meng · Accepted Answer · 2014-01-11 08:44:47Z

The problem is that you're assigning values after you've read all of the input, rather than assigning one line at a time.

Instead of

//Read file in separate parts and remove commas
while ((sCurrentLine = textReader.readLine()) != null)  {   
    array = sCurrentLine.split(",");
    System.out.print(array[0]);
    System.out.print(array[1]);
    System.out.print(array[2]);
    System.out.println(array[3]);               
}

//enter variables from each line in separate arrays
for (i = 0; i < array.length; i++) {
    id[i] = array[0];
    name[i] = array[1];
    asg1[i] = array[2];
    asg2[i] = array[3];
}

you probably want something like

int i = 0;
while ((sCurrentLine = textReader.readLine()) != null) {
    array = sCurrentLine.split(",");
    id[i] = array[0];
    name[i] = array[1];
    asg1[i] = array[2];
    asg2[i] = array[3];
    i++;
}

It's also true that by the time you reach the System.out.println in your current code, it'll be equal to one past the last index you populated, but that's a lesser issue.

Ashutosh · Accepted Answer · 2014-01-11 08:52:48Z

I assume that your Information.txt file and ReadFile.java are in same default package I edited your program like this:

import java.io.*;

class ReadFile {
public static void main(String args[]) {

    String[] id = new String[1234]; // random number just for initialization
    String[] name = new String[1234];
    String[] asg1 = new String[1234];
    String[] asg2 = new String[1234];

    try {

        String sCurrentLine;
        FileReader fr = new FileReader(ReadFile.class.getResource(
                "/Information.txt").getFile());
        BufferedReader textReader = new BufferedReader(fr);

        int i = 0;
        String[] array = null;

        // Read file in separate parts and remove commas
        while ((sCurrentLine = textReader.readLine()) != null) {
            array = sCurrentLine.split(",");

            id[i] = array[0];
            name[i] = array[1];
            asg1[i] = array[2];
            asg2[i] = array[3];

            i++;
        }

        for(int j=0;j<i;j++){
            System.out.println(id[j] + " , " + name[j] + " , " + asg1[j] + " , " + asg2[j]);
        }
        textReader.close();
    }

    // Catch exception if any
    catch (Exception e) {
        System.err.println("Error: " + e.getMessage());
    }
}

}

Ashutosh · Accepted Answer · 2014-01-11 11:54:43Z

1

In case you require a double array, you should declare the array as double in the first place like this:

double[] asg1 = new double[100];

then you can use this:

asg1[i] = Double.parseDouble(array[2]);

answered Jan 11, 2014 at 11:54

Ashutosh

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2 Comments

user3184556 Over a year ago

It says "Error: For input string: "Asg1" Any idea what that means?

Ashutosh Over a year ago

This means parseDouble is not reading a double value. This error may occur because of the very first line. You need to put an if() to make sure parseDouble works on all lines except the first line

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