/**
     * Close an application-managed entity manager. 
     * After the close method has been invoked, all methods
     * on the <code>EntityManager</code> instance and any 
     * <code>Query</code>, <code>TypedQuery</code>, and
     * <code>StoredProcedureQuery</code> objects obtained from 
     * it will throw the <code>IllegalStateException</code>
     * except for <code>getProperties</code>, 
     * <code>getTransaction</code>, and <code>isOpen</code> (which will return false).
     * If this method is called when the entity manager is
     * joined to an active transaction, the persistence
     * context remains managed until the transaction completes. 
     * @throws IllegalStateException if the entity manager
     *         is container-managed
     */
    public void close();