Question

我有这段代码：

private void discountButtonActionPerformed(java.awt.event.ActionEvent evt) {
    double purchasePrice, discount, discountAmount;
    DecimalFormat x = new DecimalFormat("$##.00");

    purchasePrice = Double.parseDouble(inputPurchase.getText());
    discount = 0.1;

    if (purchasePrice < 10) {
        outputDiscountAmount.setText(x.format(0));
        outputPrice.setText(x.format(purchasePrice));
    } else {
        outputDiscountAmount.setText(x.format(purchasePrice * discount));
        discountAmount = purchasePrice - Double.parseDouble(outputDiscountAmount.getText());
        outputPrice.setText(x.format(discountAmount));

        //Not sure whether the discountAmount variable should be in the "else" 
        //brackets or at the top.  If it is at the top nothing works.
        //If where it is presently seen, outputDiscountAmount works, but outputPrice doesn't.
        //Don't know what's wrong.
    }
}

我正在使用NetBeans 8.2作为GUI，并在JButton中。

可以看到我的评论，outputPrice无效。我没有看到任何错误怎么了？该代码应该为超过10美元的购买提供10％折扣的价格，并输出新的成本。如果购买低于10美元，没有折扣。谢谢

Answer 1

我们假设purchasePrice = 10.00：

outputDiscountAmount.setText(x.format(purchasePrice * discount));

现在outputDiscountAmount = $ 1.00。

discountAmount = purchasePrice - Double.parseDouble(outputDiscountAmount.getText());

此行抛出NumberFormatException，因为$ 1.00不是有效数字。

现在我们已经确定了问题，你应该能够做其余的事情。如果您不确定how，这是一个有用的链接。

Answer 2

您无法为数字解析无效字符（在本例中为'$'）。您的代码失败了NumberFormatException，如另一个答案中所述。

查找下面的完整代码。在这里，折扣计算为单独的双变量，然后格式化以显示在折扣标签上。

package test;

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class PriceDiscountSwing implements ActionListener{

    private JLabel outputDiscountAmount;
    private JLabel outputPrice;

    private JTextField inputPurchase;

    private JButton discountButton;
    JFrame frame = null;

    public PriceDiscountSwing(){
        initUI();
    }

    private void initUI(){
        frame = new JFrame ();

        inputPurchase = new JTextField(20);

        outputDiscountAmount = new JLabel();

        outputPrice = new JLabel();

        JPanel panel = new JPanel();
        panel.add(inputPurchase);
        panel.add(outputDiscountAmount);
        panel.add(outputPrice);

        discountButton = new JButton("Find Discount");
        discountButton.addActionListener(this);

        frame.add(panel, BorderLayout.CENTER);
        frame.add(discountButton, BorderLayout.SOUTH);

        frame.setSize(500, 500);
        frame.setVisible(true);
    }

    private void discountButtonActionPerformed(java.awt.event.ActionEvent evt) {
        double purchasePrice, discount, discountAmount;
        DecimalFormat x = new DecimalFormat("$##.00");

        String priceEnterred = inputPurchase.getText();
        if (priceEnterred.trim().length() > 0){
            purchasePrice = Double.parseDouble(priceEnterred.trim());
            discount = 0.1;

            if (purchasePrice < 10) {
                outputDiscountAmount.setText("Discount: " + x.format(0d));
                outputPrice.setText("Price: " + x.format(purchasePrice));
            } else {
                double actualDiscount = purchasePrice * discount;
                outputDiscountAmount.setText("Dicount: " + x.format(actualDiscount));
                //discountAmount = purchasePrice - Double.parseDouble(outputDiscountAmount.getText());
               discountAmount = purchasePrice - actualDiscount;
                outputPrice.setText("Price: " + x.format(discountAmount));

                //Not sure whether the discountAmount variable should be in the "else" 
                //brackets or at the top.  If it is at the top nothing works.
                //If where it is presently seen, outputDiscountAmount works, but outputPrice doesn't.
                //Don't know what's wrong.
            }
        }else{
            JOptionPane.showMessageDialog(frame, "Please enter some amount");
        }
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource().equals(discountButton)){
            discountButtonActionPerformed(e);           
        }
    }

    public static void main (String []args){
        new PriceDiscountSwing();
    }
}

没有明显的错误，但GUI仍然无法正常工作？

2 个答案: