How to display faint gray “ghost text” in a JTextField?

For what it’s worth, I found it interesting to actually implement it, so I thought to share it with you (I am not looking for votes).

It’s really non-invasive since all you have to do is call new GhostText(textField, "Please enter some text here...");. The rest of the code is only to make it run.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;

public class Test {

    public static class GhostText implements FocusListener, DocumentListener, PropertyChangeListener {
        private final JTextField textfield;
        private boolean isEmpty;
        private Color ghostColor;
        private Color foregroundColor;
        private final String ghostText;

        protected GhostText(final JTextField textfield, String ghostText) {
            super();
            this.textfield = textfield;
            this.ghostText = ghostText;
            this.ghostColor = Color.LIGHT_GRAY;
            textfield.addFocusListener(this);
            registerListeners();
            updateState();
            if (!this.textfield.hasFocus()) {
                focusLost(null);
            }
        }

        public void delete() {
            unregisterListeners();
            textfield.removeFocusListener(this);
        }

        private void registerListeners() {
            textfield.getDocument().addDocumentListener(this);
            textfield.addPropertyChangeListener("foreground", this);
        }

        private void unregisterListeners() {
            textfield.getDocument().removeDocumentListener(this);
            textfield.removePropertyChangeListener("foreground", this);
        }

        public Color getGhostColor() {
            return ghostColor;
        }

        public void setGhostColor(Color ghostColor) {
            this.ghostColor = ghostColor;
        }

        private void updateState() {
            isEmpty = textfield.getText().length() == 0;
            foregroundColor = textfield.getForeground();
        }

        @Override
        public void focusGained(FocusEvent e) {
            if (isEmpty) {
                unregisterListeners();
                try {
                    textfield.setText("");
                    textfield.setForeground(foregroundColor);
                } finally {
                    registerListeners();
                }
            }

        }

        @Override
        public void focusLost(FocusEvent e) {
            if (isEmpty) {
                unregisterListeners();
                try {
                    textfield.setText(ghostText);
                    textfield.setForeground(ghostColor);
                } finally {
                    registerListeners();
                }
            }
        }

        @Override
        public void propertyChange(PropertyChangeEvent evt) {
            updateState();
        }

        @Override
        public void changedUpdate(DocumentEvent e) {
            updateState();
        }

        @Override
        public void insertUpdate(DocumentEvent e) {
            updateState();
        }

        @Override
        public void removeUpdate(DocumentEvent e) {
            updateState();
        }

    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                init();
            }
        });
    }

    public static void init() {
        JFrame frame = new JFrame("Test ghost text");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel();
        JTextField textField = new JTextField();
        JButton button = new JButton("Grab focus");
        GhostText ghostText = new GhostText(textField, "Please enter some text here...");
        textField.setPreferredSize(new Dimension(300, 24));
        panel.add(textField);
        panel.add(button);
        frame.add(panel);
        frame.pack();
        frame.setVisible(true);
        button.grabFocus();
    }
}