code: @SuppressWarnings({ "rawtypes", "unchecked" })
  	@Override
  	public PrefixedPropertiesEnumeration<?> propertyNames() {
  		lock.readLock().lock();
  		try {
  			final Set result = new HashSet();
  			for (final Object key : getKeyMap(false).keySet()) {
  				result.add(getUnprefixedKey(key));
  			}
  			return new PrefixedPropertiesEnumerationImpl(result.iterator(), true);
  		} finally {
  			lock.readLock().unlock();
  		}
  	}
docs: /*
  (non-Javadoc)
  
  @see java.util.Properties#propertyNames()