Question

这个简单的程序应该能够获得标记百分比和批发成本并计算零售价格我将动作监听器放到 CALCULATE 按钮但是当我按下计算按钮时会出现此错误：

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: 
For input string: "Enter the markup precentage" 
at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source) 
at java.lang.Double.parseDouble(Unknown Source) 
at mm$CalcListerner.actionPerformed(mm.java:58) 
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) 
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) 
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) 
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)

有人可以帮我解决这个问题吗？

有人可以解释这些错误信息，因为我真的没有得到任何这些错误信息吗？

我的代码是：

import javax.swing.*;
import java.awt.event.*;

public class mm extends JFrame {

    private JTextField WholesaleCost;
    private JTextField markupPresentage;
    private JLabel WCost;
    private JLabel MPrecentage;
    private JButton button;
    private JPanel pannel;
    private final int Width = 250;
    private final int height = 320;

    public mm() {
        setTitle("Retail Price Calculator");
        setSize(Width, height);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
        buildPanel();
        add(pannel);
    }

    private void buildPanel() {
        WholesaleCost = new JTextField(10);
        markupPresentage = new JTextField(10);

        WCost = new JLabel("enter the Whole Sale cost");
        MPrecentage = new JLabel("Enter the markup precentage");

        button = new JButton("Calculate");
        button.addActionListener(new CalcListerner());

        pannel = new JPanel();
        pannel.add(WholesaleCost);
        pannel.add(markupPresentage);
        pannel.add(WCost);
        pannel.add(MPrecentage);
        pannel.add(button);
    }

    private class CalcListerner implements ActionListener {

        public void actionPerformed(ActionEvent e) {
            String WSaleinput;
            String MPres;
            WSaleinput = WholesaleCost.getText();
            MPres = MPrecentage.getText();

            double Value = Double.parseDouble(WSaleinput) * (Double.parseDouble(MPres) / 100);

            JOptionPane.showMessageDialog(null, "Retail Price is  " + Value);
        }
    }

    public static void main(String[] args) {
        mm x = new mm();
    }
}

Answer 1

您正在尝试将MPrecentage.getText（）解析为double，但这是您的标签的值，而不是输入的值。

您应该将MPres设置为markupPercentage.getText();

如果jvm无法从您提供的字符串中获取数字，则会引发错误NumberFormatException。在这种情况下，您尝试从“输入标记百分比”

文本中解析一个数字

Answer 2

您正试图引用错误的组件。

此

WSaleinput=WholesaleCost.getText();
MPres =MPrecentage.getText();

实际应该是

WSaleinput = WholesaleCost.getText();
MPres = markupPresentage.getText();

这个简单的GUI程序出错

2 个答案: