CODEWITHSUNDEEP
javaarraysvariable-length-array
Sahin
Sahin

Reputation: 61

The unknown size of array

In Java, I am trying to read files and then I want to put them in an array. But when I declare an array, an error occurs because of unknown length. Here's an example:

Object unsortedInt[];
        try {
            BufferedReader bR = new BufferedReader(new FileReader(x));
            String values = bR.readLine();
            int index=0;
            while (values != null){
                unsortedInt[index]=values;
                values= bR.readLine();
                index++;
            }
            bR.close();
        }
        catch (IOException e) {
            e.printStackTrace();
        }

I can work with arraylist for this problem but is there a way that works with arrays ?

Upvotes: 1

Views: 755

Answers (3)

Madushan Perera
Madushan Perera

Reputation: 2598

You can try something like below :

public class AddItemToArray {

    private int[] list = new int[0];//you should initialize your array first. 

    public int[] getList() {
        return list;
    }

    public void push(int i) {
        int fLen = list.length;//you can check the current length of your array and add your value to the next element of your array with the copy of previous array
        list = Arrays.copyOf(list, list.length + 1);
        list[fLen] = i;

    }

    public static void main(String[] args) {

        AddItemToArray myArray = new AddItemToArray();
        myArray.push(10);
        myArray.push(20);
        myArray.push(30);
        System.out.println(Arrays.toString(myArray.getList()));

    }
}

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1500245

I can work with arraylist for this problem but is there a way that works with arrays ?

Only by reproducing the logic of ArrayList, basically. No, there's no way of getting a variable-length array. Arrays in Java just don't support that.

If you need an array later, you could create an ArrayList and then call toArray to create the array afterwards.

You could read the file once just to count the lines and then again to actually read the data... but it would be much better just to use an ArrayList while you read.

Upvotes: 2

Eran
Eran

Reputation: 393781

In order to work with arrays, you must initialize the array to some initial length. You can later create a larger array (and copy the contents of the original array to it) if the current array is too small for your input. That's the way ArrayList is implemented.

Upvotes: 2

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