Problem with PrintWriter and another Problem with Inputhandling

[Daniel Siepmann]

Hello,

I'm new to Java and a "jung" boy from Germany. So sorry for my bad english.

Ok, I've got two Problems:
1.
I save the Informations from my Program to a txt-File.

    PrintWriter pw = new PrintWriter(saveFile);
    for (i = 0, j = elements.size(); i < j; i++) {
        pw.println(elements.get(i).getId());
        pw.println(elements.get(i).getDescription());
        pw.println(elements.get(i).getAmount());
        pw.println(elements.get(i).getPrice());
    }
    pw.close();

This saves the float-value (getPrice()) with a dot. For example 14.5
When I load the File I use this Code, same like getting the user input:

    File fileSaveFile = new File(saveFile);
    Scanner scFile = new Scanner(fileSaveFile);
    i = 0;
    do {
        uCId = scFile.nextLine();
        uCDescription = scFile.nextLine();
        uCAmount = scFile.nextInt();
        scFile.nextLine();
        uCPrice = scFile.nextFloat();
        scFile.nextLine();
        elements.add(new Element(uCId, uCDescription, uCAmount, uCPrice));
        i++;
    } while (scFile.nextLine() != null);

This want the float with a comma. For example 14,5.
I think Scanner uses the language configuration of the OS. PrintWriter uses english. How can I solve this problem?

My 2nd Problem is:
The user can make an Input and I want to handle wrong inputs. The actual code:

System.out.println("Insert informations for the new component:");
System.out.print("Id: ");
uCId = sc.nextLine();
System.out.print("Description: ");
uCDescription = sc.nextLine();
System.out.print("Number in stock: ");
uCAmount = sc.nextInt();
System.out.print("Price: ");
uCPrice = sc.nextFloat();
elements.add(new Element(uCId, uCDescription, uCAmount, uCPrice));

Of course there are Exceptions, for example at Line 07. The user writes characters... I can catch them, but I want to display the Error, and the user will get a 2nd chance to make his input. So I think I need a loop, but how can I write this?

For further informations you can take a look at the ProjectWiki. See my signature. There is a Mercurial repository and the last stable version of the program.

[Rob Spoor]

1) check out Scanner.useLocale to change the locale to Locale.US.

2) when writing use a NumberFormat to write the float, or use PrintWriter.printf when writing:

pw.printf(Locale.getDefault(), "%f%n", elements.get(i).getPrice());

Personally, I would probably use a combination of both so you always know that, no matter the system, the output matches the input. And I also wouldn't use Locale.getDefault() then but a specific one like Locale.US or Locale.GERMAN.

[Daniel Siepmann]

Big thanks. I set everything to Locale.US.

Does someone have an Idea for my 2nd "problem"?

[Peter Taucher]

Something like this could work:

public static void main( String[] args )
{
    Scanner scanner = new Scanner( System.in );
    int number = Integer.MIN_VALUE;
    
    System.out.println( "Provide an integer number:" );
    while( number == Integer.MIN_VALUE )
    {
        try
        {
            number = scanner.nextInt();
        }
        catch( InputMismatchException imex )
        {
            scanner.nextLine();
            System.out.println( "Wrong input (" + imex.getMessage() + "). Please try again:" );
        }
    }
    
    System.out.println( "Number: " +  number );
}

[Rob Spoor]

Or use the hasXXX methods:

public static void main( String[] args )
{
    Scanner scanner = new Scanner( System.in );
    int number = Integer.MIN_VALUE;
    
    System.out.println( "Provide an integer number:" );
    while (scanner.hasNext() && !scanner.hasNextInt())
    {
        scanner.next();
        System.out.println( "Wrong input (" + imex.getMessage() + "). Please try again:" );
    }
    // !scanner.hasNext() or scanner.hasNextInt()
    if (scanner.hasNext())
    {
        // scanner.hasNextInt()
        number = scanner.nextInt();
    }
    System.out.println( "Number: " +  number );
}