public void onBlockBreak(BlockBreakEvent event) {
   if (event.isCancelled()) return;
   Block block = event.getBlock();
   if (block.getType() == Material.BOOKSHELF) {
     AdvShelf shelf = new AdvShelf(block.getLocation());
     shelf.delete();
     ItemStack stack = new ItemStack(block.getType(), 1);
     block.getWorld().dropItemNaturally(block.getLocation(), stack);
   }
 }
 public void onBlockPlace(BlockPlaceEvent event) {
   if (event.isCancelled()) return;
   Player player = event.getPlayer();
   Block block = event.getBlockPlaced();
   if (block.getType() == Material.BOOKSHELF) {
     AdvShelf shelf = new AdvShelf(block.getLocation());
     shelf.setOwner(player.getName());
     shelf.setModifier(player.getName());
     shelf.save();
   }
 }