How do i detect am empty text field condition?

Question

Hi im a newbie with swing. I have a small problem. I have a text field. When user types some text into it i display a pane in the GUI. When the text field is cleared, i need to hide the pane. So basically i need to detect the condition when the text field is empty.
I tried one approach in which i capture key press event. So when user presses the backspace key to clear the text field, the event is fired. In the keyPress method, i check if text field is empty using getText() method.
So my keyPressed method is as follows:
keyPressed()
if(textField.getText().trim().equals(""))
     // make my pane invisible here
This does work , however it requires one additional key press before detecting that the text field is empty. For ex if there are 3 letters in the text field, i require to press the backspace key 4 times to hide the pane. I think this is because the key presses event occurs first & is handled & after that the GUI is repainted with the new data.
Any idea how i can tackle this? Or is there any other way in which i can detect the moment the text field becomes empty?

Answer 1

Demo:
import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
public class DocumentListenerExample {
    public static void main(String[] args) {
        final JLabel state = new JLabel();
        final JTextField field = new JTextField(10);
        field.getDocument().addDocumentListener(new DocumentListener(){
            public void insertUpdate(DocumentEvent e) {
                change();
            public void removeUpdate(DocumentEvent e) {
                change();
            public void changedUpdate(DocumentEvent e) {
            private void change() {
                String text = field.getText().trim();
                state.setText(text.length()==0 ? "empty field" : "non-empty field");
        JPanel cp = new JPanel(new GridLayout(1,2,8,8));
        cp.setBorder(BorderFactory.createEmptyBorder(8,8,8,8));
        cp.add(field);
        cp.add(state);
        field.setText("enter your text here");
        JFrame f = new JFrame("DocumentListenerExample");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setContentPane(cp);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
}