Java——四舍五入到小数点后两位

Question

我想将变量retail_price四舍五入到小数点后两位。我已经尝试了几次，但它总是给我一个错误。据我所知，有两种方法可以四舍五入到小数点后两位。对于这个例子，我实际上只需要使用它一次。导入还是不导入会更好？帮助

        // 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

您可以使用 DecimalFormat 来实现这一点。首先像这样初始化它:

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

而不是打印 Retail_price 使用此:

df.format(retail_price)

请记住，如果您想要进行可靠的金钱计算，您应该使用 BigDecimal 而不是 double。