if else語句中出現意外結果

Question

我是一個初學者，因此得到這個結果是因為我的if if陳述令我震驚。 除了當QtyCalc變量> = 100時的條件之外，其他所有東西都可以正常工作。Finprice變量被列為光盤變量，我不知道為什么。 救命？

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

當數量> = 100時，最終價格等於折扣，因為折扣為50％...請查看您發布的代碼。 尤其是：

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

Answer 2

沒有奇怪的行為，只有簡單的數學運算：

        disc = (preprice * (0.5));
        Finprice = (preprice - disc);

您還應該考慮消除冗余代碼：

import javax.swing.JOptionPane;
public class SoftwareSales {
    public static void main(String[] args) {
        final int PRICE = 99;
        String qty;
        double qtyCalc, preprice, finprice, disc;
        disc = 0;
        qtyCalc = 0;

        boolean invalid = false;
        do{
            invalid = false;
            qty = JOptionPane.showInputDialog(null, "How many packages will you buy?");
            if (qty == null){
                return;
            }
            try{
                qtyCalc = Double.parseDouble(qty);          
            }catch(NumberFormatException e){
                invalid = true;
            }
        }while(invalid);

        preprice = qtyCalc * PRICE;
        if (qtyCalc >= 100) {
            disc = (preprice * (0.5));
        } else if (qtyCalc >= 50 && qtyCalc <= 99) {
            disc = (preprice * 0.4);
        } else if (qtyCalc >= 20 && qtyCalc <= 49) {
            disc = (preprice * 0.3);
        } else if (qtyCalc >= 10 && qtyCalc <= 19) {
            disc = (preprice * 0.2);
        } 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);
            return;
        } else {
            JOptionPane.showMessageDialog(null, "You have entered an invalid number.");
            return;
        }

        finprice = (preprice - disc);
        JOptionPane.showMessageDialog(null, String.format("Your discount is: %.2f.\nYour final price is: %.2f. ",disc,finprice));

    }
}

還請記住變量的Java約定：始終以小寫開頭。 總決賽大寫