关于 BlueJ 中按钮的几个问题

Question

我的问题是当我选择它时，我的单选按钮会在 java 终端中导致一个巨大的错误。它在开始按钮（按钮 1 到按钮 4）按钮 1 启动加油站（所以你可以选择你想要的气体类型），但不是打开单选按钮可供选择，它给了我一堆错误涉及到

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String

单选按钮之前工作过，但在我制作了 checkboxes 方法之后它停止工作，但复选框选择工作（但是不清除）。 发现错误，属于这个

litres=Double.parseDouble(gasL.getText());

所以我暂时删除了该部分，但不确定如何使其工作，因为我试图从用户可以输入的文本框中获取升数。油条还是打不开

清除适用于复选框，但我不确定单选按钮，这给了我错误

这是我的代码

    import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
/**
 * A GUI for a Gas Bar, which allows you to choose the gas type you want, and optional car checks for things like 
 * windshield and gas check. The price is outputted afterwards.
 * 
 * @author Kevin Hy 
 * @date   08/06/13
 */
public class New_Gas_Bar extends JFrame
{
    public JPanel panel1,panel2,panel3,panel4,panel5;
    public JLabel main1, main2, main3,main4,main5,main6;
    public JLabel gasBar,total;
    public JButton button1,button2,button3,button4,clearGas,clearCar;
    public JRadioButton bronzeG,silverG,goldG,selfS,fullS,fullService,selfService;
    public JCheckBox oilC,windWash,pressureClock;
    public JTextField gasL;
    static double fullCost,selfCost,discount,gasCost,litres,cleaningC;
    static boolean boughtGas=false;

    public New_Gas_Bar()
    {
        super ("      New Gas Bar");
        setSize(640,640);
        Container container = getContentPane();

        panel1=new JPanel();
        panel2=new JPanel();
        panel3=new JPanel();
        panel4=new JPanel();
        panel5=new JPanel();

        panel1.setBackground(new Color(107,202,226));
        panel1.setLayout(new GridLayout(6,1));

        main1 = new JLabel ("         Gas Bar Project ");
        main2 = new JLabel ("         ICS4U0 - September 2013");
        main3 = new JLabel ("     ");
        main4 = new JLabel ("Enter Litres of Gas");
        main5 = new JLabel ("Select Full or Self Serve");
        main6 = new JLabel ("Select Gas Quality");

        button1 = new JButton ("Gas Station");
        button2 = new JButton ("Car Wash");
        button3 = new JButton ("Total");
        button4 = new JButton ("Exit");
        clearCar = new JButton ("Clear");
        clearGas = new JButton ("Clear");

        panel2.setBackground(new Color(144,160,170));
        panel2.setLayout(new FlowLayout ());
        panel2.add (button1);
        panel2.add (button2);
        panel2.add (button3);
        panel2.add (button4);
        panel1.add (main1);
        panel1.add (main2);
        panel1.add (main3);

        //container.setLayout(new BorderLayout());
        container.add(panel1,BorderLayout.NORTH);
        container.add(panel2,BorderLayout.CENTER);
        container.add(panel3,BorderLayout.EAST);
        container.add(panel4,BorderLayout.EAST);
        panel3.setBackground(new Color(107,202,226));
        panel4.setBackground(new Color(107,202,226));

        ButtonHandler handler = new ButtonHandler ();
        button1.addActionListener (handler);
        button2.addActionListener (handler);
        button3.addActionListener (handler);
        button4.addActionListener (handler);
        clearCar.addActionListener (handler);
clearGas.addActionListener (handler);
        ButtonGroup serveStyle = new ButtonGroup();
        fullS = new JRadioButton ("Full Serve");
        selfS = new JRadioButton ("Self Serve");
        serveStyle.add (fullS);
        serveStyle.add (selfS);

        ButtonGroup serveGas = new ButtonGroup();
        bronzeG = new JRadioButton("Bronze Service");
        silverG = new JRadioButton("Silver Service");
        goldG = new JRadioButton("Gold Service");
        serveGas.add (bronzeG);
        serveGas.add (silverG);
        serveGas.add (goldG);

        gasL = new JTextField(5);
        oilC = new JCheckBox("Oil Change");
        windWash = new JCheckBox("Windshield Wash");
        pressureClock = new JCheckBox("Air Pressure Check");

        RadioButtonHandler radioHand = new RadioButtonHandler ();
        bronzeG.addItemListener (radioHand);
        silverG.addItemListener (radioHand);
        goldG.addItemListener (radioHand);
        fullS.addItemListener (radioHand);
        selfS.addItemListener (radioHand);
        CheckBoxHandler checkHand = new CheckBoxHandler();
        oilC.addItemListener (checkHand);
        windWash.addItemListener (checkHand);
        pressureClock.addItemListener (checkHand);
        setVisible(true);
    }

    public static void main (String [] args)
    {

        New_Gas_Bar application = new New_Gas_Bar();    
    }

    public class ButtonHandler implements ActionListener

    {
        public void actionPerformed (ActionEvent event)
        {
            if (event.getSource () == button1)
            {           
                panel1.setVisible(true);
                panel2.setVisible(true);
                panel3.setVisible(true);
                panel4.setVisible(false);
                panel3.setLayout(new GridLayout(10,1));
                panel3.add(clearGas);
                panel3.add(main5);
                panel3.add(fullS);
                panel3.add(selfS);
                panel3.add(main6);
                panel3.add(bronzeG);
                panel3.add(silverG);
                panel3.add(goldG);
                panel3.add(main4);
                panel3.add(gasL);

                litres=Double.parseDouble(gasL.getText());
                //JOptionPane.showMessageDialog (null, litres);
            }
            else if (event.getSource () == button2)
            {
                panel1.setVisible(true);
                panel2.setVisible(true);
                panel3.setVisible(false);
                panel4.setVisible(true);
                panel4.setLayout(new FlowLayout ());
                panel4.add(clearCar);
                panel4.add(oilC);
                panel4.add(windWash);
                panel4.add(pressureClock);
            }
            else if (event.getSource () == button3)
            {
                JOptionPane.showMessageDialog (null, "This is your total:");
                JOptionPane.showMessageDialog (null, litres);
            }
            else if (event.getSource () == button4)
            {
                System.exit(0);
            }
            if (event.getSource () == clearGas)
            {
                JOptionPane.showMessageDialog (null, "Clearing All Selected Options");
                bronzeG.setSelected(false);
                silverG.setSelected(false);
                goldG.setSelected(false);
                fullS.setSelected(false);
                selfS.setSelected(false);
                gasCost=0;
                boughtGas=false;
            }
            if (event.getSource () == clearCar)
            {
                JOptionPane.showMessageDialog (null, "Clearing All Selected Options");
                pressureClock.setSelected(false);
                windWash.setSelected(false);
                oilC.setSelected(false);
                cleaningC=0;
            }
        }
    }
    public class RadioButtonHandler implements ItemListener

    {
        public void itemStateChanged(ItemEvent event)
        {
            if (event.getSource () == fullS)
            {        
                JOptionPane.showMessageDialog (null, "Full Serve Selected");
                fullCost =1.25;
                boughtGas=true;
            }

            else if (event.getSource () == selfS)
            {
                JOptionPane.showMessageDialog (null, "Self Serve Selected");
                selfCost =0.60;
                boughtGas=true;
            }
            if (event.getSource () == bronzeG)
            {           
                JOptionPane.showMessageDialog (null, "Bronze Gas Option Selected");
                gasCost=0.50;
                boughtGas=true;
            }
            if (event.getSource () == silverG)
            {
                JOptionPane.showMessageDialog (null, "Silver Gas Option Selected");
                gasCost=0.75;
                boughtGas=true;
            }
            if (event.getSource () == goldG)
            {
                JOptionPane.showMessageDialog (null, "Gold Gas Option Selected");
                gasCost=0.95;
                boughtGas=true;
            }

        }
    }
    public class CheckBoxHandler implements ItemListener

    {
        public void itemStateChanged (ItemEvent event)
        {
            if (event.getSource () == oilC)
            {           
                JOptionPane.showMessageDialog (null, "Oil Cleaning Selected");
                if (boughtGas==true)
                {
                    cleaningC+=10.00;
                }
                else 
                {
                    cleaningC+=12.50;
                }
            }
            if (event.getSource () == windWash)
            {
                JOptionPane.showMessageDialog (null, "Windshield Washing Selected");
                if (boughtGas==true)
                {
                    cleaningC+=10.00;
                }
                else 
                {
                    cleaningC+=12.50;
                }
            }
            if (event.getSource () == pressureClock)
            {
                JOptionPane.showMessageDialog (null, "Air Pressure Check Selected");
                if (boughtGas==true)
                {
                    cleaningC+=10.00;
                }
                else 
                {
                    cleaningC+=12.50;
                }
            }

        }
    }
}

Answer 1

看看你得到的错误。它说 NumberFormatException。我相信问题出在你的 Double.parseDouble(gasL.getText()) 上。当gasL留空时会发生什么？程序如何将空字符串解析为双精度字符串？尝试将gasL的默认值设置为0或查看try/catch来处理异常。

gasL = new JTextField("0",5);

这会删除错误消息，但我无法弄清楚为什么您的加油站面板没有打开，对此感到抱歉。

Answer 2

我认为最好不要使用诸如：Double.parseDouble() 直接之类的方法。

当然，您不会想开发自己的方法来解析双打等。

我喜欢做的是将空字符串甚至空值映射为零。

public static double myParseDouble(String s) {
    if (s == null || s.equals("")) {
        return 0.0;
    } else {
        return Double.parseDouble(s);
    }

}

在解析整数、浮点数、长整数和 BigInteger 时，您必须做同样的事情。

我建议你在自己的项目中采用我的方法，并“玩弄它”，通过它运行各种字符串，看看它做了什么。

如果您需要有关此练习或其他人的更多帮助，可以发送电子邮件至：kaydell@yahoo.com

我在教授编程方面最大的成功是使用比论坛和电子邮件更具交互性的软件。我喜欢使用聊天和屏幕共享，我可以在我的屏幕上演示如何做某事，然后学生可以在我指导时做类似的事情。