Transparent JButton

button.setOpaque(false);
button.setContentAreaFilled(false);
button.setBorderPainted(false);

The following should do the trick.

public class PlainJButton extends JButton {

    public PlainJButton (String text){
        super(text);
        setBorder(null);
        setBorderPainted(false);
        setContentAreaFilled(false);
        setOpaque(false);
    }

    // sample test method
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        JPanel pane = new JPanel();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pane.add(new PlainJButton("HI!!!!"));
        frame.add(pane);
        frame.pack();
        frame.setVisible(true);
    }
}