Question

Here’s my code:

public void readFile() throws IOException {
    System.out.println("Input file name: ");
    Scanner in = new Scanner(System.in);
    String readName = in.nextLine();
    Scanner reader = new Scanner(new File(readName));
    System.out.println("Reading file...");
    while (reader.hasNextLine()) {
        System.out.println(reader.nextLine());
    }
    System.out.println("File read.");
    Scanner inAgain = new Scanner(System.in);
    System.out.println("Would you like to read this into the current Diary?");
    System.out.println("Warning: This will overwrite your current Diary!");
    String readFileConfirm = inAgain.nextLine();
    ArrayList<String> readData = new ArrayList<String>();
    if (readFileConfirm.equalsIgnoreCase("yes")) {
        for (int i = 0; i < readData.size(); i++) {
            readData.add(reader.nextLine());
        }
        System.out.println("Data added to extra array...");
        System.out.println("Here are the contents.");
        for (int i = 0; i < readData.size(); i++) {
            System.out.println(readData.get(i));
        }
        System.out.println("Contents read.");
        System.out.println("Now overwriting current Diary with read file...");
        diary.clear();
        for (int i = 0; i < diary.size(); i++) {
            diary.add(readData.get(i));
        }
        System.out.println("New Diary created!");
        System.out.println("Use 'recall' to see your new Diary!");
    } else {
        System.out.println("Very well, returning to first command entry.");
    }
}

Answer 1

Look at:

ArrayList<String> readData = new ArrayList<String>();
if (readFileConfirm.equalsIgnoreCase("yes")) {
    for (int i = 0; i < readData.size(); i++) {
        readData.add(reader.nextLine());
    }

You’re calling readLine while i < readData, but readData starts empty so the loop never runs. Your loop should be based on the input, not the empty and resizable ArrayList. Look at Scanner.hasNextLine.

You have a similar issue later:

diary.clear();
for (int i = 0; i < diary.size(); i++) {
    diary.add(readData.get(i));
}

diary.size() starts at zero, so the loop will never run. Also, if diary is an ArrayList, it looks like you can just do:

diary = readData;

If it’s another Collection, you can do:

diary.clear()
diary.addAll(readData);

That will simply add all the elements in readData to diary.