How to make sure that JTextField contains only letters?

Question

I want to take only letters as a input in my name field.

I have already tried using the matches method but unfortunately something is wrong and the exception is being thrown.

Is there any other method of checking the same?

   import java.awt.BorderLayout;
   import java.awt.FlowLayout;
   import java.awt.GridBagConstraints;
   import java.awt.GridBagLayout;
   import java.awt.GridLayout;
   import java.awt.Insets;
   import java.awt.event.ActionEvent;
   import java.awt.event.ActionListener;
   import javax.swing.*;


    public class CreateAccount extends JFrame implements ActionListener{

    JPanel details = new JPanel(new GridBagLayout());

    JLabel fName= new JLabel("First Name:");
    JTextField firstNameField = new JTextField(10);

    JLabel lName= new JLabel("Last Name:");
    JTextField lastNameField = new JTextField(10);

    JLabel initialDeposit = new JLabel("Initial Deposit: ");
    JTextField initialDepositField = new JTextField(10);

    String accountTypes[] = {"Savings","Current"};

    JComboBox accountTypesComboBox = new JComboBox(accountTypes);
    JLabel accountType= new JLabel("Account type: ");

    JButton submit = new JButton("SUBMIT");
    JButton review = new JButton("REVIEW");

    Administrator admin = new Administrator();
    User u[] = new User[admin.maxNumberOfUsers];

    CreateAccount() {
        buildGui();
        setSize(400,300);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    public void initialiseUserCount() {
        admin.numberOfSavingsAccount = 0;
        admin.numberOfCurrentAccount = 0;
        admin.numberOfUsers=0;
    }
    public void buildGui() {

        setTitle("New Account Form");

        //JPanel submitPanel = new JPanel();
        //submitPanel.add(submit);


        GridBagConstraints c = new GridBagConstraints();
        c.insets=new Insets(10,10,10,10);
        // Stretch components horizontally (but not vertically) 
        c.fill = GridBagConstraints.HORIZONTAL;
        // Components that are too short or narrow for their space
        // Should be pinned to the northwest (upper left) corner
        c.anchor = GridBagConstraints.NORTHWEST;
        // Give the "last" component as much space as possible
        c.weightx = 1.0;

        c.gridx=0;
        c.gridy=0;
        details.add(fName,c);
        c.gridx=1;
        c.gridy=0;
        details.add(firstNameField,c);
        c.gridx=0;
        c.gridy=1;
        details.add(lName,c);
        c.gridx=1;
        c.gridy=1;
        details.add(lastNameField,c);
        c.gridx=0;
        c.gridy=2;
        details.add(initialDeposit,c);
        c.gridx=1;
        c.gridy=2;
        details.add(initialDepositField,c);
        c.gridx=0;
        c.gridy=3;
        details.add(accountType,c);
        c.gridx=1;
        c.gridy=3;
        details.add(accountTypesComboBox,c);
        c.gridx=0;
        c.gridy=4;
        details.add(submit,c);
        c.gridx=1;
        c.gridy=4;
        details.add(review,c);
        add(details);

        firstNameField.addActionListener(this);
        review.addActionListener(this);

    }
    public void actionPerformed(ActionEvent e) {
        if(e.getSource()==firstNameField) {
            try {
                String uFName = firstNameField.getText().toString();

                if(!uFName.matches("[A-Za-z]+"))
                    throw new Exception();
            }
            catch(Exception e1) {
                firstNameField.setText("");
                JOptionPane.showMessageDialog(firstNameField,"Please enter a valid name!");
            }
        }
    }
}

Answer 1

You can try to use this regex

if(!uFName.matches("^[a-zA-Z]+$"))

Answer 2

Use a DocumentFilter. It will allow you to perform real time validation of the text fields

See Implementing a Document Filter and DocumentFilter Examples for more details

For example...

public class CharFilter extends DocumentFilter {

    public void insertString(DocumentFilter.FilterBypass fb, int offset,
                    String string, AttributeSet attr)
                    throws BadLocationException {

        StringBuffer buffer = new StringBuffer(string);
        for (int i = buffer.length() - 1; i >= 0; i--) {
            char ch = buffer.charAt(i);
            if (!Character.isLetter(ch)) {
                buffer.deleteCharAt(i);
            }
        }
        super.insertString(fb, offset, buffer.toString(), attr);
    }

    public void replace(DocumentFilter.FilterBypass fb,
                    int offset, int length, String string, AttributeSet attr) throws BadLocationException {
        if (length > 0) {
            fb.remove(offset, length);
        }
        insertString(fb, offset, string, attr);
    }
}

And applied using something like...

JTextField firstNameField = new JTextField(20);
((AbstractDocument)firstNameField.getDocument()).setDocumentFilter(new CharFilter());