Prevent a character from showing up in textfield

Question

Hi,
I have a textfield..and the max # of characters allowed should be 15....so how can I stop the user from being able to enter any more characters after 15?
I tried the keyPressedEvent(KeyEvent e) {
if (fifteencharacters == true)
e.consume();
but it doesnt work.
thanks

Answer 1

The DocumentSizeFilter class is straight out of the tutorial.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
public class FilterTest
    public static void main(String[] args)
        JTextField filterField = new JTextField(16);
        AbstractDocument doc = (AbstractDocument)filterField.getDocument();
        doc.setDocumentFilter(new DocumentSizeFilter(15));
        JTextField plainField = new JTextField(16);
        JPanel north = new JPanel();
        north.add(filterField);
        JPanel south = new JPanel();
        south.add(plainField);
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setJMenuBar(getMenuBar());
        f.getContentPane().add(north, "North");
        f.getContentPane().add(south, "South");
        f.setSize(300,200);
        f.setLocation(200,200);
        f.setVisible(true);
    private static JMenuBar getMenuBar()
        JMenu edit = new JMenu("edit");
        edit.add(cut);
        edit.add(copy);
        edit.add(paste);
        JMenuBar menuBar = new JMenuBar();
        menuBar.add(edit);
        return menuBar;
    private static Action cut = new TextAction("cut")
        public void actionPerformed(ActionEvent e)
            getFocusedComponent().cut();
    private static Action copy = new TextAction("copy")
        public void actionPerformed(ActionEvent e)
            getFocusedComponent().copy();
    private static Action paste = new TextAction("paste")
        public void actionPerformed(ActionEvent e)
            getFocusedComponent().paste();
* A 1.4 class used by TextComponentDemo.java. From java turorial.
class DocumentSizeFilter extends DocumentFilter
    int maxCharacters;
    boolean DEBUG = false;
    public DocumentSizeFilter(int maxChars)
        maxCharacters = maxChars;
    public void insertString(FilterBypass fb, int offs,
                             String str, AttributeSet a) throws BadLocationException
        if (DEBUG)
            System.out.println("in DocumentSizeFilter's insertString method");
        //This rejects the entire insertion if it would make
        //the contents too long. Another option would be
        //to truncate the inserted string so the contents
        //would be exactly maxCharacters in length.
        if ((fb.getDocument().getLength() + str.length()) <= maxCharacters)
            super.insertString(fb, offs, str, a);
        else
            Toolkit.getDefaultToolkit().beep();
    public void replace(FilterBypass fb, int offs, int length,
                        String str, AttributeSet a) throws BadLocationException
        if (DEBUG)
            System.out.println("in DocumentSizeFilter's replace method");
        //This rejects the entire replacement if it would make
        //the contents too long. Another option would be
        //to truncate the replacement string so the contents
        //would be exactly maxCharacters in length.
        if ((fb.getDocument().getLength() + str.length() - length) <= maxCharacters)
            super.replace(fb, offs, length, str, a);
        else
            Toolkit.getDefaultToolkit().beep();
}