How to set JTextField to show certain map scale (e.g. 1/2000)

Question

Hi,folks. I have a JTextField instance. How can I set the format to only allow user to only type the map scale(e.g. 1/2000). I can only use the JTextField component. Thank you in advance.

Answer 1

I think the regex you're looking for is"1/[1-9]\\d*"Note that in the regex you posted"1[\\]\\d*"the closing bracket is quoted by the backslash, causing the error you mentioned. Not that you needed a backslash there anyways.
You can try this, but note that since replace(...) invokes remove(...) and replace(...), pasting an apparently valid String will not succeed if the slash is part of the replacement. Also that setText or pasting are the only ways to set the initial content as you won't be able to type it in one character at a time.import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;
public class ScaleFactorTextField {
   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         @Override
         public void run() {
            new ScaleFactorTextField().makeUI();
   public void makeUI() {
      JTextField textField = new JTextField(10);
      textField.setDocument(new PlainDocument() {
         final Pattern p = Pattern.compile("1/[1-9]\\d*");
         @Override
         public void insertString(int offs, String str, AttributeSet a)
               throws BadLocationException {
            String newText = getText(0, offs) + str +
                  getText(offs, getLength() - offs);
            if (isValidText(newText)) {
               super.insertString(offs, str, a);
         @Override
         public void remove(int offs, int len) throws BadLocationException {
            String newText = getText(0, offs) +
                  getText(offs + len, getLength() - offs - len);
            if (isValidText(newText)) {
               super.remove(offs, len);
         @Override
         public void replace(int offs, int len, String text,
               AttributeSet attrs) throws BadLocationException {
            String newText = getText(0, offs) + text +
                  getText(offs + len, getLength() - offs - len);
            if (isValidText(newText)) {
               super.replace(offs, len, text, attrs);
         private boolean isValidText(String text) {
            Matcher m = p.matcher(text);
            return m.matches();
      textField.setText("1/20000");
      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.add(textField);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
}db