java - if else 语句出现意外结果

Question

我是一名初学者，所以我在 if else 语句的一个条件下得到的结果让我大吃一惊。除了 QtyCalc 变量 >= 100 的条件外，一切正常。Finprice 变量被列为光盘变量，我不明白为什么。帮助？

import javax.swing.JOptionPane;
public class SoftwareSales {
    public static void main(String[] args) {
        final int price = 99;
        String Qty;
        double QtyCalc, preprice, Finprice, disc;

        Qty = JOptionPane.showInputDialog(null, "How many packages will you buy?");
        QtyCalc = Double.parseDouble(Qty);
        preprice = QtyCalc * price;

        if (QtyCalc >= 100) {
            disc = (preprice * (0.5));
            Finprice = (preprice - disc);
            JOptionPane.showMessageDialog(null, "Your discount is: " + disc + ".\n" + "Your final price is: " + Finprice + ". ");
        } else if (QtyCalc >= 50 && QtyCalc <= 99) {
            disc = (preprice * 0.4);
            Finprice = (preprice - disc);
            JOptionPane.showMessageDialog(null, "Your discount is: " + disc + ".\n" + "Your final price is: " + Finprice + ". ");
        } else if (QtyCalc >= 20 && QtyCalc <= 49) {
            disc = (preprice * 0.3);
            Finprice = (preprice - disc);
            JOptionPane.showMessageDialog(null, "Your discount is: " + disc + ".\n" + "Your final price is: " + Finprice + ". ");
        } else if (QtyCalc >= 10 && QtyCalc <= 19) {
            disc = (preprice * 0.2);
            Finprice = (preprice - disc);
            JOptionPane.showMessageDialog(null, "Your discount is: " + disc + ".\n" + "Your final price is: " + Finprice + ". ");
        } else if (QtyCalc < 10 && QtyCalc >= 1) {
            disc = 0;
            Finprice = 0;
            JOptionPane.showMessageDialog(null, "Sorry, there is no discount for purchases less than 10." + " Your price is: " + preprice);

        } else {
            JOptionPane.showMessageDialog(null, "You have entered an invalid number.");
        }
        disc = 0;
        Finprice = 0;

        System.exit(0);
    }
}

Answer 1

当数量 >= 100 时，最终价格等于折扣，因为折扣为 50% ...查看您发布的代码。特别是:

if (QtyCalc >= 100) {
    disc = (preprice * (0.5));
    Finprice = (preprice - disc);
    JOptionPane.showMessageDialog(null, "Your discount is: " + disc + ".\n" + "Your final price is: " + Finprice + ". ");
}