Alphabets validation of jtextfield

Question

I have been trying to just display the alphabets in the jtextfield.Even though the other keys are pressed the jtextfield should not display them only the alphabets are to be displayed.can you please help me with this..

Answer 1

Start by taking a look at Implementing a Document Filter

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

public class TestFilter {

    public static void main(String[] args) {
        new TestFilter();
    }

    public TestFilter() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JTextField field = new JTextField(10);
                ((AbstractDocument)field.getDocument()).setDocumentFilter(new CharFilter());

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new GridBagLayout());
                frame.add(field);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class CharFilter extends DocumentFilter {

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

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

        @Override
        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);
        }
    }
}

You ma also find DocumentFilter Examples helpful

Answer 2

here is a solution if you want only alphabets to be entered to a jtextfield,and no other keys should be entered even though they get pressed.in your jframe just select your jtextfield rightclick on jtextfield you will find events and then go to events click on keyTyped event and then write the following code to enter only the alphabets into your jtextfield.

private void tfempidKeyTyped(java.awt.event.KeyEvent evt) {
// TODO add your handling code here:

    char key = evt.getKeyChar();
    if (key > '0' && key < '9') {
        evt.consume();
    }