Adding a watermark to an empty JCombobox

I'm trying to reproduce the behavior of the search field of Firefox or Safari, or the search field of stackoverflow.com on the top 开发者_如何学Pythonright of this page.

I mean, when there is no text on the editable JComboBox, an instruction text is displayed, like "Type here" or whatever. When the JComboBox is focused the text is removed. If the focus is lost with no text typed, the instruction text comes back.

Note:

Check out Text Prompt for a more complete implementation of the code below with more features.

Here's something simple I threw together. I'm sure you can tidy it up. Since the code works on a JTextField, you would need to get the editor of the combobox. I no nothing about how Glazed lists is implemented so I'm just guessing it will work for you.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.event.*;
import javax.swing.text.*;

public class TextPrompt extends JLabel
    implements FocusListener, DocumentListener
{
    private JTextComponent component;
    private Document document;

    public TextPrompt(String text, JTextComponent component)
    {
        this.component = component;
        document = component.getDocument();

        setText( text );
        setFont( component.getFont() );
        setBorder( new EmptyBorder(component.getInsets()) );

        component.addFocusListener( this );
        document.addDocumentListener( this );

        component.add( this );
    }

    public void checkForPrompt()
    {
        if (document.getLength() == 0)
            setSize( component.getSize() );
        else
            setSize(0, 0);
    }

//  Implement FocusListener

    public void focusGained(FocusEvent e)
    {
        checkForPrompt();
    }

    public void focusLost(FocusEvent e)
    {
        setSize(0, 0);
    }

//  Implement DocumentListener

    public void insertUpdate(DocumentEvent e)
    {
        checkForPrompt();
    }

    public void removeUpdate(DocumentEvent e)
    {
        checkForPrompt();
    }

    public void changedUpdate(DocumentEvent e) {}

    public static void main(String[] args)
    {
        JPanel panel = new JPanel();
        JTextField tf1 = new JTextField(10);
        panel.add(tf1);
        JTextField tf2 = new JTextField(10);
        panel.add(tf2);

        new TextPrompt("First Name", tf1);
        new TextPrompt("Last Name", tf2);

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.add(panel);
        frame.pack();
        frame.setLocationRelativeTo( null );
        frame.setVisible(true);
    }
}

Its called a waterMark. jQuery has one. I've never tired to apply a watermark to a jComboBox.
Good luck