code: @SuppressWarnings("unchecked")
  	@Override
  	public PrefixedPropertiesEnumeration<Object> keys() {
  		lock.readLock().lock();
  		try {
  			@SuppressWarnings("rawtypes")
  			final Set keys = keySet();
  			@SuppressWarnings("rawtypes")
  			final Iterator it = keys.iterator();
  			return new PrefixedPropertiesEnumerationImpl<Object>(it, true);
  		} finally {
  			lock.readLock().unlock();
  		}
  	}
docs: /*
  (non-Javadoc)
  
  @see java.util.Hashtable#keys()