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public class TestPlugin extends JavaPlugin {
    @Override
    public void onEnable() {
        getServer().getPluginManager().registerEvents(new Listener() {
            @EventHandler(ignoreCancelled = true)
            public void onPlayerMove(PlayerMoveEvent event) {
                Location to = event.getTo();
                if (to == null) {
                    return; // i don't even know...
                }
                Location from = event.getFrom();
                if (to.getWorld() == from.getWorld() &&
                        to.getBlockX() == from.getBlockX() &&
                        to.getBlockY() == from.getBlockY() &&
                        to.getBlockZ() == from.getBlockZ()) {
                    return; // did not move
                }

                Player player = event.getPlayer();
                ItemStack handItem = player.getInventory().getItemInMainHand();
                if (handItem.getType() == Material.AIR) {
                    return; // nothing in hand
                }

                BlockData data = player.getWorld().getPlacementBlockData(handItem.getType().createBlockData(), to);
                player.sendMessage(data.getAsString());
            }
        }, this);
    }
}