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.