So I have this to convert String from JTextField to int. It says Exception in thread "main" java.lang.NumberFormatException: For input string: "". Please help.
JTextField amountfld = new JTextField(15);
gbc.gridx = 1; // Probably not affecting anything
gbc.gridy = 3; //
add(amountfld, gbc);
String amountString = amountfld.getText();
int amount = Integer.parseInt(amountString);
From docs:
Throws: NumberFormatException - if the string does not contain a parsable integer.
The empty String "" is not a parsable integer, so your code will always produce a NumberFormatException if no value is entered.
There are many ways in which you can avoid this. You can simply check if the String value you got from amountField.getText() is actually populated. You can create a custom IntegerField, which only allows integers as input, but adding Document to a JTextField. Create a Document to only allow integers an input:
public static class IntegerDocument extends PlainDocument {
@Override
public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
StringBuilder sb = new StringBuilder(str.length());
for (char c:str.toCharArray()) {
if (!Character.isDigit(c)) {
sb.append(c);
}
}
super.insertString(offs, sb.toString(), a);
}
}
Now create a IntergerField with a convenient getInt method, which returns zero if nothing is entered:
public static class IntegerField extends JTextField {
public IntegerField(String txt) {
super(txt);
setDocument(new IntegerDocument());
}
public int getInt() {
return this.getText().equals("") ? 0 : Integer.parseInt(this.getText());
}
}
Now you can retrieve the integer value from amountField without doing any checks:
JTextField amountField = new IntegerField("15");
...
//amount will be zero if nothing is entered
int amount = amountField.getInt();
Your biggest problem is that you're parsing the text field contents immediately after creating the field, and this makes no sense. Wouldn't it make much more sense to parse the data after allowing the user the opportunity to enter data, preferably within a listener of some sort, often an ActionListener?
And so my recommendations are two-fold
NumberFormatException. If an exception occurs, you then clear the JTextField by calling setText(), and then warn the user that they're entering invalid data, often done with a JOptionPane.For example:
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import javax.swing.*;
@SuppressWarnings("serial")
public class GetNumericData extends JPanel {
private JTextField amountfld = new JTextField(15);
private JSpinner amountSpinner = new JSpinner(new SpinnerNumberModel(0, 0, 40, 1));
private JButton submitButton = new JButton(new SubmitAction("Submit"));
private JButton exitButton = new JButton(new ExitAction("Exit", KeyEvent.VK_X));
public GetNumericData() {
add(new JLabel("Amount 1:"));
add(amountfld);
add(new JLabel("Amount 2: $"));
add(amountSpinner);
add(submitButton);
add(exitButton);
}
// do all your parsing within a listener such as this ActionListener
private class SubmitAction extends AbstractAction {
public SubmitAction(String name) {
super(name);
int mnemonic = (int) name.charAt(0);
putValue(MNEMONIC_KEY, mnemonic);
}
@Override
public void actionPerformed(ActionEvent e) {
String amountTxt = amountfld.getText().trim();
try {
int amount1 = Integer.parseInt(amountTxt);
// if this parse fails we go immediately to the catch block
int amount2 = (Integer) amountSpinner.getValue();
String message = String.format("Your two amounts are %d and %d", amount1, amount2);
String title = "Amounts";
int messageType = JOptionPane.INFORMATION_MESSAGE;
JOptionPane.showMessageDialog(GetNumericData.this, message, title, messageType);
} catch (NumberFormatException e1) {
String message = "You can only enter numeric data within the amount field";
String title = "Invalid Data Entered";
int messageType = JOptionPane.ERROR_MESSAGE;
JOptionPane.showMessageDialog(GetNumericData.this, message, title, messageType);
amountfld.setText("");
}
}
}
private class ExitAction extends AbstractAction {
public ExitAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
}
@Override
public void actionPerformed(ActionEvent e) {
System.exit(0);
}
}
private static void createAndShowGui() {
JFrame frame = new JFrame("Get Data");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new GetNumericData());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> createAndShowGui());
}
}
