why initialize this byte array to 1024

Question

I'm relatively new to Java and I'm attempting to write a simple android app. I have a large text file with about 3500 lines in the assets folder of my applications and I need to read it into a string. I found a good example about how to do this but I have a question about why the byte array is initialized to 1024. Wouldn't I want to initialize it to the length of my text file? Also, wouldn't I want to use char, not byte? Here is the code:

private void populateArray(){
    AssetManager assetManager = getAssets();
    InputStream inputStream = null;
    try {
        inputStream = assetManager.open("3500LineTextFile.txt");
    } catch (IOException e) {
        Log.e("IOException populateArray", e.getMessage());
    }
    String s = readTextFile(inputStream);
    // Add more code here to populate array from string
}

private String readTextFile(InputStream inputStream) {
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    inputStream.length
    byte buf[] = new byte[1024];
    int len;
    try {
        while ((len = inputStream.read(buf)) != -1) {
            outputStream.write(buf, 0, len);
        }
        outputStream.close();
        inputStream.close();
    } catch (IOException e) {
        Log.e("IOException readTextFile", e.getMessage());
    }
    return outputStream.toString();
}

EDIT: Based on your suggestions, I tried this approach. Is it any better? Thanks.

private void populateArray(){
    AssetManager assetManager = getAssets();
    InputStream inputStream = null;
    Reader iStreamReader = null;
    try {
        inputStream = assetManager.open("List.txt");
        iStreamReader = new InputStreamReader(inputStream, "UTF-8");
    } catch (IOException e) {
        Log.e("IOException populateArray", e.getMessage());
    }
    String String = readTextFile(iStreamReader);
    // more code here
}

private String readTextFile(InputStreamReader inputStreamReader) {
    StringBuilder sb = new StringBuilder();
    char buf[] = new char[2048];
    int read;
    try {
        do {
            read = inputStreamReader.read(buf, 0, buf.length);
            if (read>0) {
                sb.append(buf, 0, read);
            }
        } while (read>=0);
    } catch (IOException e) {
        Log.e("IOException readTextFile", e.getMessage());
    }
    return sb.toString();
}

Answer 1

This example is not good at all. It's full of bad practices (hiding exceptions, not closing streams in finally blocks, not specify an explicit encoding, etc.). It uses a 1024 bytes long buffer because it doesn't have any way of knowing the length of the input stream.

Read the Java IO tutorial to learn how to read text from a file.

Answer 2

You are reading the file into a buffer of 1024 Bytes. Then those 1024 bytes are written to outputStream. This process repeats until the whole file is read into the outputStream. As JB Nizet mentioned the example is full of bad practices.