Java —将钱四舍五入到小数点后两位

Question

I want to round the variable retail_price to 2 decimal places. I have tried a few times and it always gives me an error. As far as I know there are two ways to round to 2 decimal places. For this instance I really only need to use it once. Would it still be better to import it or no?? Help

        // The actionPerformed method executes when the user clicks the calculate button
    public void actionPerformed(ActionEvent e)
    {
        double retail_price;
        String input1;
        String input2;

        // Get the number from the users input in priceFeild1
        input1 = priceField1.getText();

        // Get the number from the users input in priceFeild2
        input2 = priceField2.getText();

        // Calculate out the priceFeilds to find the retail price.
        retail_price = Double.parseDouble(input1) + ((Double.parseDouble(input1) * (Double.parseDouble(input2) / 100)));

        // Show the results
        JOptionPane.showMessageDialog(null, "The whole sale cost of the item is: $" + input1 + ". "
                                                + "\nThe markup percentage of the item is: " +  input2 + "%." 
                                                + "\nIf those two numbers were correct, the retail price is: $" + retail_price);            
    }

Answer 1

You can use DecimalFormat to achieve that. First initialize it like that:

final DecimalFormat df = new DecimalFormat("#.##");

than instead of printing retail_price use this:

df.format(retail_price)

Remember that if you want to have a reliable money calculations you should use BigDecimal instead of double.

Answer 2

Try

// Show the results
        JOptionPane.showMessageDialog(null, String.format("The whole sale cost of the item is: $%.2f. "
                                                + "\nThe markup percentage of the item is: %s%%." 
                                                + "\nIf those two numbers were correct, the retail price is: $%.2f", Double.parseDouble(input1), input2, retail_price));  

Answer 3

这将进行舍入。

retail_price = Math.round(retail_price * 100.0) / 100.0;

Answer 4

Here's how I did it in one line.

double amount = Double.Parse(String.format("%.2f", 20.4425);

For basic purposes this is more than enough. Let me break it down.

double amountIn = 20.4425;
String amountInString = String.format("%.2f", amountIn);
double amountOut = Double.parse(amountInString);

String.format() converts the double into a 2 decimal string, then Parse turns it back into a double. Simple efficient and easy to do.