How to limit number of characters in a JTextField?

Question

Hi,
I am new to java and I would like to create a JTextField which only allows the users to enter no more than 32 characters. How do I do that? I am looking for a "set..." function but cannot find it.
Thanks for any hint.
Richard

Answer 1

Unfortunately there's no setXXX() method that will do it. You'll need to create a new document class that will accomplish what you want. See attached sample working code.
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
import javax.swing.text.*;
public class Limit {
public static void main(String args[]) {
  new LimitFrame();
class LimitFrame extends JFrame {
JTextField jtf = new JTextField(10);
LimitFrame() {
  super();
  jtf.setDocument(new LimitDocument(5));
  /* Components should be added to the container's content pane */
  Container cp = getContentPane();
  cp.add(BorderLayout.NORTH,jtf);
  /* Add the window listener */
  addWindowListener(new WindowAdapter() {
   public void windowClosing(WindowEvent evt) {
    dispose(); System.exit(0);}});
  /* Size the frame */
  pack();
  /* Center the frame */
  Dimension screenDim = Toolkit.getDefaultToolkit().getScreenSize();
  Rectangle frameDim = getBounds();
  setLocation((screenDim.width - frameDim.width) / 2,(screenDim.height - frameDim.height) / 2);
  /* Show the frame */
  setVisible(true);
class LimitDocument extends PlainDocument
int limit;
public LimitDocument(int limit)
  this.limit = limit;
public void insertString(int offset, String s, AttributeSet a) throws BadLocationException
  if (offset + s.length() <= limit)
   super.insertString(offset,s,a);
  else
   Toolkit.getDefaultToolkit().beep();
}