Question

I need to not allow any characters to be entered after X have been typed. I need to send a beep after X characters have been typed. I know how to do this after the user presses enter, but I need to do it before the user presses enter. The approach I found from Oracle’s site is to add a DocumentSizeFilter to the JTextPane. I can’t get this to notify the user when they have gone over (it doesn’t work until they press enter). This is a sample of what I have.

public class EndCycleTextAreaRenderer extends JTextPane
implements TableCellRenderer {

private final int maxNumberOfCharacters = 200;

public EndCycleTextAreaRenderer() {
    StyledDocument styledDoc = this.getStyledDocument();
    AbstractDocument doc;
    doc = (AbstractDocument)styledDoc;
    doc.setDocumentFilter(new DocumentSizeFilter(maxNumberOfCharacters ));

}

Answer 1

Override the insertString method of the document in the JTextPane so that it doesn’t insert any more characters once the maximum has been reached.

For example:

JTextPane textPane = new JTextPane(new DefaultStyledDocument() {
    @Override
    public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
        if ((getLength() + str.length()) <= maxNumberOfCharacters) {
            super.insertString(offs, str, a);
        }
        else {
            Toolkit.getDefaultToolkit().beep();
        }
    }
});

Update:

You can change your class as follows:

public class EndCycleTextAreaRenderer extends JTextPane implements TableCellRenderer {

    private final int maxNumberOfCharacters = 200;

    public EndCycleTextAreaRenderer() {
        setStyledDocument(new DefaultStyledDocument() {
            @Override
            public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
                if ((getLength() + str.length()) <= maxNumberOfCharacters) {
                    super.insertString(offs, str, a);
                } else {
                    Toolkit.getDefaultToolkit().beep();
                }
            }
        });
    }
}