Move ChunkLoadEvent to separate ChunkListener class

src/main/java/com/songoda/ultimatestacker/UltimateStacker.java

@@ -281,6 +281,7 @@ public class UltimateStacker extends SongodaPlugin {
                 }
             }
         });
+        getServer().getPluginManager().registerEvents(new ChunkListener(this), this);
     }
 
     public void addExp(Player player, EntityStack stack) {

src/main/java/com/songoda/ultimatestacker/listeners/BlockListeners.java

@@ -47,14 +47,6 @@ public class BlockListeners implements Listener {
         this.plugin = plugin;
     }
 
-    @EventHandler
-    public void onChunkLoad(ChunkLoadEvent event) {
-        if (!Settings.STACK_BLOCKS.getBoolean()) return;
-        Chunk chunk = event.getChunk();
-        BlockStackManager blockStackManager = plugin.getBlockStackManager();
-        blockStackManager.getStacks().stream().filter(stack -> stack.getLocation().getChunk().equals(chunk)).forEach(plugin::updateHologram);
-    }
-
     @EventHandler(priority = EventPriority.HIGHEST)
     public void onBlockInteract(PlayerInteractEvent event) {
         if (event.useInteractedBlock() == Event.Result.DENY) return;

src/main/java/com/songoda/ultimatestacker/listeners/ChunkListener.java

@@ -0,0 +1,28 @@
+package com.songoda.ultimatestacker.listeners;
+
+import com.songoda.ultimatestacker.UltimateStacker;
+import com.songoda.ultimatestacker.settings.Settings;
+import com.songoda.ultimatestacker.stackable.block.BlockStackManager;
+import org.bukkit.Chunk;
+import org.bukkit.event.EventHandler;
+import org.bukkit.event.Listener;
+import org.bukkit.event.world.ChunkLoadEvent;
+
+public class ChunkListener implements Listener {
+
+    private final BlockStackManager blockStackManager;
+    private final UltimateStacker plugin;
+
+    public ChunkListener(UltimateStacker plugin) {
+        this.blockStackManager = plugin.getBlockStackManager();
+        this.plugin = plugin;
+    }
+
+    @EventHandler
+    public void onChunkLoad(ChunkLoadEvent event) {
+        if (!Settings.STACK_BLOCKS.getBoolean()) return;
+        Chunk chunk = event.getChunk();
+        BlockStackManager blockStackManager = plugin.getBlockStackManager();
+        blockStackManager.getStacks().stream().filter(stack -> stack.getLocation().getChunk().equals(chunk)).forEach(plugin::updateHologram);
+    }
+}

src/main/java/com/songoda/ultimatestacker/stackable/block/BlockStackManager.java

@@ -8,10 +8,11 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 public class BlockStackManager {
 
-    private final Map<Location, BlockStack> registeredBlocks = new HashMap<>();
+    private final Map<Location, BlockStack> registeredBlocks = new ConcurrentHashMap<>();
 
     public void addBlocks(Map<Location, BlockStack> blocks) {
         this.registeredBlocks.putAll(blocks);