Limit number of character in a TextArea

Question

Hi,
how can I limited the number of character in a jTextArea?
thanks!

Answer 1

You have to customize the Document that your text area is using. You can read more about the Document interface here:
http://java.sun.com/j2se/1.5.0/docs/api/javax/swing/text/Document.html
And here is a simple example that demonstrates how you can customize a Document to do what you want. The program should compile and run as is. It will display a JTextArea that only allows ten characters.
import javax.swing.*;
import javax.swing.text.*;
public class LimitedTextArea extends JFrame {
    public LimitedTextArea() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        JTextArea text = new JTextArea(5, 40);
        // Set the customized Document on the text area. Only allow
        // a maximum of ten characters:
        text.setDocument(new LimitedDocument(10));
        getContentPane().add(new JScrollPane( text ));
        pack();
        setLocationRelativeTo(null);
    public static void main(String[] args) {
        new LimitedTextArea().setVisible(true);
    // Document that only allows a certain number of characters
    class LimitedDocument extends PlainDocument {
        private int maxLength;
        public LimitedDocument(int maxLength) {
            this.maxLength = maxLength;
        // This method is overriden from the super class. It will be called when
        // you are trying to insert text in your text component (by typing
        // or pasting).
        public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
            int currentLength = getLength();
            if( currentLength >= maxLength ) {
                // There's not room for more characters. Return.
                return;
            if( currentLength + str.length() > maxLength ) {
                // All of the characters we are trying to insert will not fit.
                // We must trim the string.
                str = str.substring(0, maxLength - currentLength);
            // Insert the text:
            super.insertString(offs, str, a);
}