Assignment with file input

Question

I'm not one to join boards for the purpose of asking a question, but it's here that I'm stumped, and if anyone could help, I'd really appreciate it. Here's the first part of the task:
"Task-
Imagine that you are an owner of a hardware store and need to keep an
inventory that can tell you what different kind of tools you have how many of
each you have on hand and cost of each one.
Now do the following:
(1) Write a program (Tool.java) that,
(1.1) Initializes (and creates) a file ?hardware.dat?
(1.2) lets you input that data concerning each tool, i.e. the
program must ask the user for input and each of the user
input is written back in the file.
The file must have the following format:
Record# Tool Name Qty Cost per item (A$)
1 Electric Sander 18 35.99
2 Hammer 128 10.00
3 Jigsaw 16 14.25
4 Lawn mower 10 79.50
5 Power saw 8 89.99
6 Screwdriver 236 4.99
7 Sledgehammer 32 19.75
8 Wrench 65 6.48
(1.3) Exception handling that must be taken into account-
(1.3.1) User must not input incorrect data
(1.3.2) Cost of the item must be a number"
My code is below. So, here's my problem.
1. I tried using "isNaN" to check if the value for "quantity" is a number or not, but it produced a "cannot find symbol method" or some such, hence why I used a try and catch thing.
The problem is, the statement in the second try thing only tests it hypothetically; i.e. it tests it, but if it IS a number, it doesn't enter a value at all. If it ISN'T a number, it properly catches the exception.
But if I do the "nextInt" after the try and catch, I'll have to enter a new line. How can I do the catch, but also enters the value if it's true? "isNaN" would be the best method... and I'll separate everything into their own modules soon.
2. I have the tool Name, Quantity, and Price. However, I'm unsure how to add the record number. The program can be run at any time to add a record once at a time, so the record number needs to reflect what you're adding.
3. In the second part, "ToolDetails" reads and displays the contents of the "hardware.dat" file which the records are written to, and it also displays the total cost of all items, i.e. "Total toolName[1] cost: toolQuantity[1]*toolPrice[1]".
4. Also in the second class "ToolDetails", there needs to be a way to select a specific record by the toolName and delete all details pertaining to it, for example, you choose "Wrench", then the program deletes the record number, quantity, and price of "Wrench".
I apologise for my choppy code, it's what I've pieced together while testing out things. Can anyone please help me or provide guidance on where to research these things? Thanks a lot.
import java.io.*;
import java.util.Scanner;
import java.lang.Exception;
public class Tool
     public static void main(String[] args)
          PrintWriter outputStream = null;
          try
               outputStream = new PrintWriter(new FileOutputStream("hardware.dat", true));
          catch(FileNotFoundException error)          // The above may throw an error.
          {                                             // Hence, the exception catching.
               System.out.println("File hardware.dat not found.");
               System.exit(0);
          Scanner toolInput = new Scanner(System.in);
          System.out.println("Enter tool name:");
          String toolName = toolInput.nextLine();          
          System.out.println("Enter quantity:");          
          String test = toolInput.nextInt().toString;
          try
               int toolQuantity = toolInput.nextInt();
          catch(java.util.InputMismatchException ime)
               System.out.println("Not a number.");
               System.exit(0);
          int toolQuantity = toolInput.nextInt();
          System.out.println("Enter price of item:");
          double toolPrice = toolInput.nextDouble();
          outputStream.println(toolName + "   " + toolQuantity + "   " + toolPrice);
          outputStream.close();
          System.out.println("\nThank you, new item \"" + toolName + "\" entered.");
}

Answer 1

Hi,
A couple of things:
- don't put everything in the main method; you end up duplicating code and one huge method is hard to follow. Use separate methods instead.
- when using Scanners nextInt() or nextDouble() method, it will leave the lineseparator in place which will then "clutter up" the Scanner.
For example if the user enteres "123" and hits the return button, the String will really look like this: "123\r\n" (depending on the OS). If you now call nextInt(), the number 123 will be returned and the "\r\n" will still be in the Scanner and when the user enters another number, say 6.6 and hits return, the Scanner will then look like this: "\r\n6.6\r\n". Calling Scanners nextDouble() method will now be the cause of an exception being thrown.
You still with me?
So, I advise you to just read a complete line from the user with Scanners nextLine() method, and try to convert that line into a number and catch a possible NumberFormatException.
Here's a little start. I already wrote one method for you (getIntFromUser(...)), try to finish it now:
import java.io.*;
import java.util.Scanner;
// import java.lang.Exception; <-- java.lang.* classes are automatically imported
public class Tool {
    static final Scanner toolInput = new Scanner(System.in);
    static final String fileName = "hardware.dat";
    public static void main(String[] args) {
        String toolName = getStringFromUser("Enter tool name:");  
        int quantity = getIntFromUser("Enter quantity:");       
        double price = getDoubleFromUser("Enter price of item:");
        System.out.println("You entered: '"+toolName+"', '"+quantity+"' and '"+price+"'.");
    public static int getIntFromUser(String prompt) {
        while(true) {
            System.out.print("\n"+prompt+" ");
            String line = toolInput.nextLine();
            try {
                int number = Integer.parseInt(line);
                return number;
            } catch(NumberFormatException e) {
                System.out.println("Invalid, try again!");
    public static double getDoubleFromUser(String prompt) {
        // your code here
        return -1.0;
    public static String getStringFromUser(String prompt) {
        // your code here
        return "a tool name";
    public static String readFile() {
        // your code here
        // Have a look at http://javaalmanac.com/egs/java.io/ReadLinesFromFile.html
        // how to read the lines from a textfile.
        return "";
    public static void writeLineToFile(String extraLine) {
        // your code here
        // Note: before writing the 'extraLine' to the file, you should
        // read the current contents from it and write it all to the file
        // Have a look at http://javaalmanac.com/egs/java.io/WriteToFile.html
        // how to write to a textfile.
}Good luck.