How to reset Scanner?

Question

I want to read a text file and put each line in a String (array of Strings). However that requires scanning file twice, one to figure out how many line are there and another time to create an array of strings of that size. but it throws an error and reset method doesn't seem to work.

    FileReader read = null;

    try {
        read = new FileReader("ModulesIn.txt");
        //scan through it and make array of strings - for each line
        Scanner scan = new Scanner(read);
        while(scan.hasNextLine()){
            numOfMods++;
            scan.nextLine();
        }

        scan.reset();

        lines = new String[numOfMods];

        for(int i = 0; i < numOfMods; i++)
            lines[i] = scan.nextLine();

This is the snippet of the code that is relevant.

Answer 1

Skip using a standard array... it's a waste of time to scan through the file and then scan through again. Use an arraylist instead which has a dynamic size and then convert it to a standard array afterwards.

 BufferedReader in = new BufferedReader(new FileReader("path/of/text"));
        String str;

        List<String> list = new ArrayList<String>();
        while((str = in.readLine()) != null){
            list.add(str);
        }

        String[] stringArr = list.toArray(new String[0]);

Answer 2

"However that requires scanning file twice ..." ...

No it doesn't. See @Exziled's answer for a better (simpler, more efficient) way that doesn't scan the file twice.

But to answer your question, there is no way to reset a Scanner to the start of the stream. You would need to reset the underlying stream and then create a new Scanner. (And, of course, some kinds of stream don't support resetting.)

For the record, the Scanner.reset() method resets the scanner's delimiter, locale and number radix state. It doesn't reposition the scanner.