如何从Java中的ArrayLists读取和写入文件

Question

So I have the following read and write file program for an Array. How would the following look like for an ArrayList? I am having trouble with the syntax. I know an ArrayList would be like that: private ArrayList prod list = new ArrayList(); BUt how would the read/write IO syntax be? Thank you.

    static ActionProduct[] prodlist = new ActionProduct[50];
    static String filename = System.getProperty("user.dir") + "\\src\\product.txt";
    static int pIndex=0;


public static void readFile() throws IOException {
        // input file must be supplied in the first argument
        InputStream istream;
        if (filename.length() > 0) {
            File inputFile = new File(filename);
            istream = new FileInputStream(inputFile);
        } else {
            // if no filename, use standard input stream
            istream = System.in;
        }

        // use a buffered reader for line-at-a-time
        // reading
        BufferedReader lineReader;
        lineReader = new BufferedReader(new InputStreamReader(istream));

        // read one line at a time
        String line;
        while ((line = lineReader.readLine()) != null) {

            StringTokenizer tokens = new StringTokenizer(line, "\t");

            // String tmp = tokens.nextToken();
            // System.out.println("token " + tmp);
            prodlist[pIndex] = new ActionProduct();
            String category = prodlist[pIndex].getCategory();
            category = tokens.nextToken();
            System.out.println("got category " +category);

            int item = prodlist[pIndex].getItem();
            item = Integer.parseInt(tokens.nextToken());

            String name = prodlist[pIndex].getName();
            System.out.println("got name " +name);

            double price = prodlist[pIndex].getPrice();
            price = Double.parseDouble(tokens.nextToken());

            int units = prodlist[pIndex].getUnits();
            units = Integer.parseInt(tokens.nextToken());
            pIndex++;
        }
    }

Answer 1

Replace this:

static ActionProduct[] prodlist = new ActionProduct[50];

with

static List<ActionProduct> prodlist = new ArrayList<ActionProduct>();

then this:

        prodlist[pIndex] = new ActionProduct();

with

        ActionProduct p = new ActionProduct();
        prodlist.add(p);

Finally, replace all uses of prodlist[pIndex] with p , then get rid of pIndex everywhere else.