java - DocumentListener Java，如何防止 JTextBox 中出现空字符串？

Question

在此处输入图像描述我一直在从事一个个人项目，以便在编程方面做得更好。我的目标是让它更加健壮，我才刚刚开始。我现在是计算机科学专业的学生。无论如何，我正在制作如图所示的程序的一部分。我计算了小时工资并提供了一些我还没有实现的输出。我正在使用 DocumentListener 所以它会自动计算。当文本从框中完全删除时出现错误。我尝试使用 if 语句修复它：

 if (tipMon.equals("") || tipMon == null) {
 tipMon.setText("0");
 }

这是我到目前为止所拥有的。它还没有完成，我为菜鸟代码道歉。我在 2 个月前开始使用实际编码。

 import java.awt.GridLayout;
 import java.awt.event.ActionListener;
 import java.awt.event.ActionEvent;
 import java.awt.event.KeyListener;

 import javax.swing.JFrame;
 import javax.swing.JLabel;
 import javax.swing.JTextField;
 import javax.swing.JOptionPane;
 import javax.swing.event.DocumentEvent;
 import javax.swing.event.DocumentListener;
 import javax.swing.text.Document;
 import javax.swing.text.FieldView;

 public class deliveryDocListener extends JFrame implements ActionListener, 
DocumentListener{

private JLabel mon, tues, wed, thurs, fri, sat, sun, hourlyWage, blank, row2, monWage,
    tuesWage,wedWage,thursWage, friWage, satWage, sunWage, total, totalTips, totalHours, 
    totalHourlyEarnings, totalPay, weekPay;

private JTextField hourlyWageInput, tipMon, tipTues, tipWed, tipThurs, tipFri, tipSat, tipSun,
    hourMon, hourTues, hourWed, hourThurs, hourFri, hourSat, hourSun;


public deliveryDocListener(){
    super("Delivery Helper v0.1 Alpha");
    setLayout(new GridLayout(0,4));

    hourlyWage = new JLabel("Hourly Wage: ");
    add(hourlyWage);
    hourlyWageInput = new JTextField("7.25", 5);

    add(hourlyWageInput);
    blank = new JLabel();
    add(blank);
    blank = new JLabel();
    add(blank);

    row2 = new JLabel("Day of the Week");
    add(row2);
    row2 = new JLabel("Tips");
    add(row2);
    row2 = new JLabel("Hours Worked");
    add(row2);
    row2 = new JLabel("Hourly Earnings");
    add(row2);

    mon = new JLabel("Monday");
    add(mon);



    tipMon = new JTextField("0");

    Document tipMonListener = tipMon.getDocument();
    //Document class doc variable stores what happens in the getDocument()
    //method, getDocument() i think is what checked it real time we shall see
    tipMonListener.addDocumentListener(this);
    //add listener to he text field, this refers to most recent object (tipMon = new JTextField("0");"
    //notice how its purple is the same as new where the object got made?
    add(tipMon);

    hourMon = new JTextField("0");
    Document hourMonListener = hourMon.getDocument();
    hourMonListener.addDocumentListener(this);
    add(hourMon);


    monWage = new JLabel("0");
    add(monWage);

    tues = new JLabel("Tuesday");
    add(tues);
    tipTues = new JTextField("0");
    add(tipTues);
    hourTues = new JTextField("0");
    add(hourTues);
    tuesWage = new JLabel("0");
    add(tuesWage);

    wed = new JLabel("Wednesday");
    add(wed);
    tipWed = new JTextField("0");
    add(tipWed);
    hourWed = new JTextField("0");
    add(hourWed);
    wedWage = new JLabel("0");
    add(wedWage);

    thurs = new JLabel("Thursday");
    add(thurs);
    tipThurs = new JTextField("0");
    add(tipThurs);
    hourThurs = new JTextField("0");
    add(hourThurs);
    thursWage = new JLabel("0");
    add(thursWage);

    fri = new JLabel("Friday");
    add(fri);
    tipFri = new JTextField("0");
    add(tipFri);
    hourFri = new JTextField("0");
    add(hourFri);
    friWage = new JLabel("0");
    add(friWage);

    sat = new JLabel("Saturday");
    add(sat);
    tipSat = new JTextField("0");
    add(tipSat);
    hourSat = new JTextField("0");
    add(hourSat);
    satWage = new JLabel("0");
    add(satWage);

    sun = new JLabel("Sunday");
    add(sun);
    tipSun = new JTextField("0");
    add(tipSun);
    hourSun = new JTextField("0");
    add(hourSun);
    sunWage = new JLabel("0");
    add(sunWage);

    blank = new JLabel();
    add(blank);
    blank = new JLabel();
    add(blank);
    blank = new JLabel();
    add(blank);
    blank = new JLabel();
    add(blank);

    total = new JLabel("Total: ");
    add(total);
    totalTips = new JLabel("totalTipsOutput");
    add(totalTips);
    totalHours = new JLabel("totalHoursOutput");
    add(totalHours);
    totalHourlyEarnings = new JLabel("totalHourlyEarningsOutput");
    add(totalHourlyEarnings);

    blank = new JLabel();
    add(blank);
    blank = new JLabel();
    add(blank);
    blank = new JLabel();
    add(blank);
    blank = new JLabel();
    add(blank);

    blank = new JLabel();
    add(blank);
    blank = new JLabel();
    add(blank);
    totalPay = new JLabel("Gross Income: ");
    add(totalPay);
    weekPay = new JLabel("totalPayOutput");
    add(weekPay);

}

@Override
public void changedUpdate(DocumentEvent e) { 
    // TODO Auto-generated method stub

}

@Override
public void insertUpdate(DocumentEvent e) {
    //executes when someone enters text into input
    String tipMonStr = tipMon.getText();
    //monWage.setText(tipMonStr);
    String hourMonStr = hourMon.getText();

    double x = Double.parseDouble(tipMonStr);
    double y = Double.parseDouble(hourMonStr);
    double z = Double.parseDouble(hourlyWageInput.getText());

    if (tipMonStr.length() == 0) {
        tipMon.setText("0");
    }

    if (hourMonStr.length() == 0) {
        y = 0;
        hourMonStr = "0";
    }

    if (hourlyWageInput.getText().length() == 0) {
        z = 0;
        //String z = "0";
    }

    monWage.setText(Double.toString((z*y+x)/y));

    //bug when nothing in cell because no number (0) to use in math
}

@Override
public void removeUpdate(DocumentEvent e) {
    //executes when someone enters text into input
    String tipMonStr = tipMon.getText();
    //monWage.setText(tipMonStr);
    String hourMonStr = hourMon.getText();

    double x = Double.parseDouble(tipMonStr);
    double y = Double.parseDouble(hourMonStr);
    double z = Double.parseDouble(hourlyWageInput.getText());
    monWage.setText(Double.toString((z*y+x)/y));

    if (tipMon.equals("") || tipMon == null) {
        tipMon.setText("0");
    }

}


public void updateLog(DocumentEvent e, String action) {
    monWage.setText(Double.toString(5));
}

@Override
public void actionPerformed(ActionEvent arg0) {
    monWage.setText(Double.toString(5));

}

}

score 8 · Accepted Answer

正如@HFOE 建议的那样，InputVerifier这是正确的选择，但verify()“应该没有副作用”。相反，调用calcProduct()in shouldYieldFocus()。

 /**
 * @see http://stackoverflow.com/a/11818946/230513
 */
private class MyInputVerifier extends InputVerifier {

    private JTextField field;
    private double value;

    public MyInputVerifier(JTextField field) {
        this.field = field;
    }

    @Override
    public boolean shouldYieldFocus(JComponent input) {
        if (verify(input)) {
            field.setText(String.valueOf(value));
            calcProduct();
            return true;
        } else {
            field.setText(ZERO);
            field.selectAll();
            return false;
        }

    }

    @Override
    public boolean verify(JComponent input) {
        try {
            value = Double.parseDouble(field.getText());
            return true;
        } catch (NumberFormatException e) {
            return false;
        }
    }
}

score 7 · Accepted Answer

I'll make this an answer: I wouldn't use a DocumentListener for this purpose as it seems to me the wrong tool for the job. For one, it is continually listening and updating the results while the user is still entering data, data that is as yet incomplete, into the JTextField. Much better would be to use an ActionListener added to a JButton or to your JTextFields.

I suppose you could use a FocusListener, but even that concerns me since it is quite low-level.

Also: consider using an InputVerifier to validate your input.

Also: consider displaying your tabular data in a JTable where the 1st and 2nd columns are editable but the others are not.

Edit
I'm not sure if this is kosher, but it could work if you do your calculation from within the verifier. For example, updated for generality:

import javax.swing.*;

/**
* @see http://stackoverflow.com/a/11818183/522444
*/
public class VerifierEg {

    private static final String ZERO = "0.0";
    private JTextField field1 = new JTextField(ZERO, 5);
    private JTextField field2 = new JTextField(ZERO, 5);
    private JTextField resultField = new JTextField(ZERO, 10);

    private void createAndShowGui() {
        resultField.setEditable(false);
        resultField.setFocusable(false);

        JPanel mainPanel = new JPanel();
        final JTextField[] fields = {field1, field2};

        mainPanel.add(field1);
        mainPanel.add(new JLabel(" x "));
        mainPanel.add(field2);
        mainPanel.add(new JLabel(" = "));
        mainPanel.add(resultField);

        for (JTextField field : fields) {
            field.setInputVerifier(new MyInputVerifier(field));
        }

        JFrame frame = new JFrame("VerifierEg");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private void calcProduct() {
        double d1 = Double.parseDouble(field1.getText());
        double d2 = Double.parseDouble(field2.getText());
        double prod = d1 * d2;
        resultField.setText(String.valueOf(prod));
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                VerifierEg eg = new VerifierEg();
                eg.createAndShowGui();
            }
        });
    }

    /**
    * @see http://stackoverflow.com/a/11818946/230513
    */
    private class MyInputVerifier extends InputVerifier {

        private JTextField field;
        private double value;

        public MyInputVerifier(JTextField field) {
            this.field = field;
        }

        @Override
        public boolean shouldYieldFocus(JComponent input) {
            if (verify(input)) {
                field.setText(String.valueOf(value));
                calcProduct();
                return true;
            } else {
                field.setText(ZERO);
                field.selectAll();
                return false;
            }

        }

        @Override
        public boolean verify(JComponent input) {
            try {
                value = Double.parseDouble(field.getText());
                return true;
            } catch (NumberFormatException e) {
                return false;
            }
        }
    }
}

score 5 · Accepted Answer

使用JSpinneror JFormattedTextField，Number instance那么DocumentListener应该可以正常工作，no needed to parse String to Number instance
否则你必须使用DocumentFilterforJTextField过滤non numeric chars，其余（计数）保持不变，仍然required robust parsing String to the Number instance

java - DocumentListener Java，如何防止 JTextBox 中出现空字符串？

3 回答 3

Related

Reference