DocumentListener Java，如何防止 JTextBox 中出现空字符串? [英] DocumentListener Java, How do I prevent empty string in JTextBox?
问题描述
我一直在做一个个人项目以提高编程水平.我的目标是让它更加健壮，我才刚刚开始.我现在是一名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.从框中完全删除文本时出现错误.我尝试使用 if 语句修复它:
I have been working on a personal project to get better with programming. My goal is to make it much more robust, I am just starting. I am a current computer science student. Anyway, I am working on making a portion of the program as shown. I calculates the hourly wage and provides some outputs I havent implemented yet. I'm using DocumentListener so it it will automatically calculate. I am getting an error when the the text is removed completely from a box.I tried to fix it with the if statement:
if (tipMon.equals("") || tipMon == null) {
tipMon.setText("0");
}
这是我目前所拥有的.它还没有完成，我为菜鸟代码道歉.我 2 个月前开始实际编码.
Here is what I have so far. It's not done yet and I apologize for the noob code. I started 2 months ago with actual coding.
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));
}
}
推荐答案
我会回答这个问题:我不会将 DocumentListener 用于此目的，因为在我看来这不是该工作的错误工具.一方面，当用户仍在将数据(尚未完成的数据)输入 JTextField 时，它会持续侦听和更新结果.使用添加到 JButton 或 JTextFields 的 ActionListener 会更好.
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.
我想你可以使用 FocusListener，但即使这样我也担心，因为它是相当低级的.
I suppose you could use a FocusListener, but even that concerns me since it is quite low-level.
另外:考虑使用 InputVerifier 来验证您的输入.
Also: consider using an InputVerifier to validate your input.
另外:考虑在 JTable 中显示表格数据，其中第一列和第二列可编辑，但其他列不可编辑.
Also: consider displaying your tabular data in a JTable where the 1st and 2nd columns are editable but the others are not.
编辑
我不确定这是否符合 kosher 标准，但如果您在验证器中进行计算，它可能会起作用.例如，更新为一般性:
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;
}
}
}
}
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