TotallyGenericClassName.java

    /**
     * Called on a piston extend event.
     *
     * @param e The piston extend event.
     */
    @EventHandler(priority = EventPriority.HIGH, ignoreCancelled = true)
    public void onPistonExtend(@Nonnull final BlockPistonExtendEvent e) {
        boolean allowed = false;
        if (hasPermission(e.getBlock().getRelative(e.getDirection()).getLocation(), WorldEvent.PISTON_EXTENSION)) {
            allowed = true;
            for (Block block : e.getBlocks()) {
                if (!hasPermission(block.getLocation(), WorldEvent.PISTON_EXTENSION)) {
                    allowed = false;
                    break;
                }
            }
        }
        if (!allowed) {
            e.setCancelled(true);
        }
    }