线程"AWT-EventQueue-0" java.lang.NumberFormatException： 对于输入字符串： " "

Question

我的代码过早地抛出了预期的错误。我试图测试输入验证，但在验证发生之前我抛出了一个错误。当我试图将我的代码恢复到以前的版本时，它会抛出与我现在处理的问题相同的错误。

输入的示例

下面的代码是第137行 -明显的罪犯

int playerGuess = Integer.parseInt(playerGuessField.getText().trim());

private void guessButtonClicked(){
Validators validGuess = new Validators(this);
int guessesRemaining = Integer.parseInt(guessesRemainingField.getText());
int playerGuess = Integer.parseInt(playerGuessField.getText().trim());//error is thrown here

if(validGuess.isValidGuess(playerGuessField, "guess")){
//more code here but not necessarily relevant
}
}

//basic structure of my validators
public boolean isValidGuess(JTextComponent c, String fieldName){
try {
int validGuess = Integer.parseInt(c.getText());
if(validGuess >= 1 && validGuess <= 10){
return true;
} else {
showErrorDialog("Your " + fieldName + " must be between 1 & 10");
c.requestFocusInWindow();
return false;
}
} catch (NumberFormatException e) {
showErrorDialog("Your " + fieldName + " must be between 1 & 10");
c.requestFocusInWindow();
return false;
}
}

这是它的荣耀中的一个例外。

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "asdf"
at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
at java.base/java.lang.Integer.parseInt(Integer.java:660)
at java.base/java.lang.Integer.parseInt(Integer.java:778)
at GameGUI.guessButtonClicked(GameGUI.java:137)
at GameGUI.lambda$0(GameGUI.java:94)
at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1972)
at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2313)
at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
at java.desktop/java.awt.Component.processMouseEvent(Component.java:6617)
at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
at java.desktop/java.awt.Component.processEvent(Component.java:6382)
at java.desktop/java.awt.Container.processEvent(Container.java:2264)
at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:4993)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2322)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4825)
at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4934)
at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4563)
at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4504)
at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2308)
at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2773)
at java.desktop/java.awt.Component.dispatchEvent(Component.java:4825)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

Answer 1

底线：您需要验证您的输入。

要做到这一点，我可以想出几个选择：

选项1：使用Scanner检查输入是否为数字

Scanner scanner = new Scanner(playerGuessField.getText().trim());
if (scanner.hasNextInt()) {
int playerGuess =  scanner.nextInt();
} else {
// handle the error
}

---

选项2：在try/catch中换行137

int playerGuess = 0;
try {
playerGuess = Integer.parseInt(playerGuessField.getText().trim());
} catch (NumberFormatException nfe) {
// handle the exception
}

---

选项3：在文本字段中添加一个输入验证器

为此，您需要创建一个输入验证器

public class MyInputVerifier extends InputVerifier {
@Override
public boolean verify(JComponent input) {
String text = ((JTextField) input).getText();
try {
BigDecimal value = new BigDecimal(text);
return true; // or some other evaluation (i.e. value > 0 for positive value)
} catch (NumberFormatException e) {
return false;
}
}
}

然后，您需要将其添加到字段

field.setInputVerifier(new MyInputVerifier());

最后，您需要触发验证。这通常是在呈现表单时完成的。我的例子是使用ActionListener。

btn.addActionListener(e -> {
if (!field.getInputVerifier().verify(field)) {
System.out.println("Not valid. Clear!");
field.setText("");
}
});

---

选项4：使用DocumentListener

public class InputVerifierDemo {
private static JLabel errorMsg = new JLabel("Invalid input");
private static JFrame frame = new JFrame();
public static void main(String[] args) {
JTextField field = new JTextField(10);
//      field.setInputVerifier(new MyInputVerifier());
JButton btn = new JButton("Click Me!");
//      btn.addActionListener(e -> {
//          if (!field.getInputVerifier().verify(field)) {
//              System.out.println("Not valid. Clear!");
//              field.setText("");
//          }
//      });
JPanel panel = new JPanel();
errorMsg.setForeground(Color.RED);
errorMsg.setVisible(false);
panel.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
c.insets = new Insets(5, 0, 0, 5);
c.gridx = 1;
c.gridy = 0;
c.anchor = GridBagConstraints.SOUTH;
panel.add(errorMsg, c);
c.gridx = 1;
c.gridy = 1;
c.anchor = GridBagConstraints.CENTER;
panel.add(field, c);
field.getDocument().addDocumentListener(new DocumentListener() {
@Override
public void removeUpdate(DocumentEvent e) {
validateInput(field);
}
@Override
public void insertUpdate(DocumentEvent e) {
validateInput(field);
}
@Override
public void changedUpdate(DocumentEvent e) {
} // Not needed for plain-text fields
});
frame.getContentPane().add(panel);
frame.setSize(400, 400);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
private static void validateInput(JTextField field) {
String text = field.getText();
String pattern = "\d+";
Pattern r = Pattern.compile(pattern);
Matcher m = r.matcher(text);
if (m.matches()) {
errorMsg.setVisible(false);
} else {
errorMsg.setVisible(true);
}
}
private static class MyInputVerifier extends InputVerifier {
@Override
public boolean verify(JComponent input) {
String text = ((JTextField) input).getText();
try {
BigDecimal value = new BigDecimal(text);
return true; // or some other evaluation (i.e. value > 0 for positive value)
} catch (NumberFormatException e) {
return false;
}
}
}
}

上面的代码包含输入验证器和文档侦听器解决方案，因此您可以同时使用这两个解决方案。我个人更喜欢文档监听器，因为它更具交互性。我宁愿在输入字段时对其进行验证，而不是在所有字段都填写完毕并执行提交表单的操作之后进行验证。但是，这完全是个人喜好的问题。

我将选项#1归功于MadProgrammer。