Input from text file to array

Question

The input will be a text file with an arbitrary amount of integers from 0-9 with NO spaces. How do I populate an array with these integers so I can sort them later?

What I have so far is as follows:

BufferedReader numInput = null;
    int[] theList;
    try {
        numInput = new BufferedReader(new FileReader(fileName));
    } catch (FileNotFoundException e) {
        System.out.println("File not found");
        e.printStackTrace();
    }
    int i = 0;
    while(numInput.ready()){
        theList[i] = numInput.read();
        i++;

Obviously theList isn't initialized, but I don't know what the length will be. Also I'm not too sure about how to do this in general. Thanks for any help I receive.

To clarify the input, it will look like: 1236654987432165498732165498756484654651321 I won't know the length, and I only want the single integer characters, not multiple. So 0-9, not 0-10 like I accidentally said earlier.

My bad--meant to say 0-9, not -10.

Sam Welch
– Sam Welch

2013-04-01 18:56:08 +00:00
Commented Apr 1, 2013 at 18:56 — Sam Welch
– Sam Welch, Commented Apr 1, 2013 at 18:56

Smit · Accepted Answer · 2013-04-01 19:00:50Z

2

Going for Collection API i.e. ArrayList

ArrayList a=new Arraylist();
while(numInput.ready()){
       a.add(numInput.read());
}

edited Apr 1, 2013 at 19:00

Smit

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answered Apr 1, 2013 at 18:54

Biswajit

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6 Comments

user142162 Over a year ago

This is only part of the problem. There's also the issue of the return value of BufferedReader.read().

Sam Welch Over a year ago

So now I'm populating an array list. All is good in that department, but I'm read input as integers of two characters long. i.e. i'm getting numInput.get(0) to return 49 when it should equal 4

0__0 Over a year ago

You probably have to subtract '0' from the value returned by read. Like a.add(numInput.read() - '0');

Sam Welch Over a year ago

Thanks David! That worked and I don't know why; I wouldn't mind an explanation if you're up for one.

0__0 Over a year ago

It's a problem of ASCII encoding. Text in a text file is stored as numeric values and the character '0' is not stored with value 0. It is stored with value 48. '0' is a way to say "the ASCII value for character 0" (sort of).

|

mthmulders · Accepted Answer · 2013-04-01 18:56:26Z

0

You could use a List<Integer> instead of a int[]. Using a List<Integer>, you can add items as desired, the List will grow along. If you are done, you can use the toArray(int[]) method to transform the List into an int[].

answered Apr 1, 2013 at 18:56

mthmulders

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Comments

dantuch · Accepted Answer · 2013-04-01 19:37:50Z

0

1 . Use guava to nicely read file's 1st line into 1 String

readFirstLine

2 . convert that String to char array - because all of your numbers are one digit lengh, so they are in fact chars

3 . convert chars to integers.

4 . add them to list.

public static void main(String[] args) {

    String s = "1236654987432165498732165498756484654651321";
    char[] charArray = s.toCharArray();
    List<Integer> numbers = new ArrayList<Integer>(charArray.length);
    for (char c : charArray) {
        Integer integer = Integer.parseInt(String.valueOf(c));
        numbers.add(integer);
    }

    System.out.println(numbers);
}

prints: [1, 2, 3, 6, 6, 5, 4, 9, 8, 7, 4, 3, 2, 1, 6, 5, 4, 9, 8, 7, 3, 2, 1, 6, 5, 4, 9, 8, 7, 5, 6, 4, 8, 4, 6, 5, 4, 6, 5, 1, 3, 2, 1]

edited Apr 1, 2013 at 19:37

answered Apr 1, 2013 at 19:04

dantuch

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