How do you use BigDecimal correctly for variables?

Question

I have been working on a small program, in it you press a button and it adds .1 to a variable. I've been using a double and I keep getting super long decimals(such as 12.0000000000000001). After googling the issue I came up with the BigDecimal class. I've never used the class before so I need help. My question is how do I fix this issue?

Here's my code (I have 2 classes, this is my main class):

    public class Game extends JFrame {
private static final long serialVersionUID = 1L;

private static mainGame mainGame = new mainGame();

private static JPanel upgradeScreen = new JPanel();

private static JTabbedPane pane = new JTabbedPane();
    public static int createRate = 16;
public static double cost = 0.1;
public static int stuff = 0;
public static double  cash = 0;
public static int limit = 1000;

public static JLabel lblMoney2 = new JLabel("You have: " + cash + " Dollars to spend.");

public Game() {

    setTitle("Shooter Tycoon");
    setResizable(false);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(1100, 688);
    setLocationRelativeTo(null);

    pane.add("Main", mainGame);
    pane.add("Upgrades", upgradeScreen);
    upgradeScreen.setLayout(null);

    lblMoney2.setBounds(10, 11, 325, 14);
    upgradeScreen.add(lblMoney2);

    getContentPane().add(pane);

}

// The main method

public static void main(String[] args) {

    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                Game frame = new Game();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

public static void add() {

    if (stuff + createRate < limit) {
        stuff += createRate;
    }
    mainGame.lblStuff.setText("You have made " + stuff + " of " + limit + " Things!");
}

public static void sell() {
    if (stuff > 0) {
        cash += stuff * cost;
        stuff = 0;
        mainGame.lblMoney.setText("You have made " + cash + " Dollars!");
        mainGame.lblStuff.setText("You have made " + stuff + " of " + limit + " Things!");
        lblMoney2.setText("You have: " + cash + " Dollars to spend.");
    }

}
  }

I'm still relatively new to Java so don't judge me too hard. If it is possible to solve this without using BigDecimal then by all means use it. Thanks in advance.

There is no relation between question and code. Where is `BigDecimal` at your code? — Masudul, Dec 08 '13 at 06:00

score 0 · Accepted Answer · answered Dec 08 '13 at 06:04

0

In this particular case, you're working with money, so you can avoid the whole BigDecimak issue by just storing the number of cents as an integer instead of the number of dollars as a decimal. To display the dollar value as a string use:

String value="$"+(cents/100)+"."+(cents%100);

Note that you'll also need to account for the special case when cents%100 is between 0 and 9, so you'll want to put this code inside a method. Let me know if you need more details.

answered Dec 08 '13 at 06:04

Flight Odyssey

2,267
18
25

@MikeSamuel: Yes, I realize, please see the second paragraph of my post (the code to account for the special case is left as an exercise). Good idea to use String.format as another solution, though. – Flight Odyssey Dec 08 '13 at 06:17
Why would you re-invent a wheel? `BigDecimal` is designed to do this kind of thing, without any mucking around. – Dawood ibn Kareem Dec 08 '13 at 08:10
Thanks a ton! This was probably much easier than using a BigDecimal. I've been scouring Google all day trying to find a solution that I understood. – Tdude179 Dec 08 '13 at 08:12
1

No, it is NOT easier than using a `BigDecimal`. So you need to code in a special case for `cents % 100 < 10`. Then another special case or two for when the amount is negative. And worry about integer overflow if you have too much money. Or just use `BigDecimal` and all those problems are taken care of for you. – Dawood ibn Kareem Dec 08 '13 at 08:13
Care to use code to help explain? Because at the time of writing that comment I thought I figured it out(I tried it in one of my test projects and it worked). After implementing the system into my main program, it didn't work. I've been on this all day and I just want a solution xD. Edit:I managed to get the program working correctly, but i'd still like to know another way of doing it. – Tdude179 Dec 08 '13 at 08:25
If you'd like to show your attempt at using `BigDecimal`, I can tell you what's wrong with it, sure. – Dawood ibn Kareem Dec 08 '13 at 09:31

How do you use BigDecimal correctly for variables?

1 Answers1