private Vector buttonListeners = null;


    public void addListener(ButtonListener listener) {
        // Don't add the listener a second time if it is in the Vector.
        int i = findListener(buttonListeners, listener);
        if (i == -1) {
            if (null == buttonListeners) {
                 // stuff goes here
                buttonListeners = new Vector();
            }
            buttonListeners.addElement(listener);
        }
    }

    /**
     * Removes a listener
     * 
     * @see #addListener(ButtonListener)
     */
    public void removeListener(ButtonListener listener) {
        int i = findListener(buttonListeners, listener);
        if (i > -1) {
            buttonListeners.remove(i);
        }
        if (0 == buttonListeners.size()) {
            // stuff goes here
            buttonListeners = null;
        }
    }