import javax.swing.*; import javax.swing.text.*; import java.awt.Toolkit;public class LimitedStyledDocument extends DefaultStyledDocument {    int maxCharacters;    public LimitedStyledDocument(int maxChars) {        maxCharacters = maxChars;    }    public void insertString(int offs, String str, AttributeSet a)         throws BadLocationException {        //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 ((getLength() + str.length()) <= maxCharacters)            super.insertString(offs, str, a);        else            Toolkit.getDefaultToolkit().beep();    }}