fixes and changes

src/net/citizensnpcs/Citizens.java

@@ -113,10 +113,10 @@ public class Citizens extends JavaPlugin {
 
     @Override
     public void onDisable() {
-        // Save an despawn all NPCs
+        // Save and despawn all NPCs
         config.save();
         saveNPCs();
-        for (NPC npc : npcManager.getSpawnedNPCs())
+        for (NPC npc : npcManager.getAllNPCs())
             npc.despawn();
 
         Bukkit.getScheduler().cancelTasks(this);

src/net/citizensnpcs/EventListen.java

@@ -49,7 +49,7 @@ public class EventListen implements Listener {
         if (event.isCancelled())
             return;
 
-        for (NPC npc : npcManager.getSpawnedNPCs()) {
+        for (NPC npc : npcManager.getAllNPCs()) {
             Location loc = npc.getBukkitEntity().getLocation();
             if (event.getWorld().equals(loc.getWorld()) && event.getChunk().getX() == loc.getChunk().getX()
                     && event.getChunk().getZ() == loc.getChunk().getZ()) {

src/net/citizensnpcs/command/command/NPCCommands.java

@@ -61,10 +61,12 @@ public class NPCCommands {
             return;
         }
 
-        respawn.spawn(player.getLocation());
-        npcManager.selectNPC(player, respawn);
-        Messaging.send(player, ChatColor.GREEN + "You respawned " + StringHelper.wrap(respawn.getName())
-                + " at your location.");
+        if (respawn.spawn(player.getLocation())) {
+            npcManager.selectNPC(player, respawn);
+            Messaging.send(player, ChatColor.GREEN + "You respawned " + StringHelper.wrap(respawn.getName())
+                    + " at your location.");
+        } else
+            Messaging.sendError(player, respawn.getName() + " is already spawned at another location.");
     }
 
     @Command(

src/net/citizensnpcs/npc/CitizensNPC.java

@@ -29,10 +29,10 @@ public class CitizensNPC extends AbstractNPC {
     }
 
     @Override
-    public void despawn() {
+    public boolean despawn() {
         if (!isSpawned()) {
             Messaging.debug("The NPC with the ID '" + getId() + "' is already despawned.");
-            return;
+            return false;
         }
 
         Bukkit.getPluginManager().callEvent(new NPCDespawnEvent(this));
@@ -42,6 +42,7 @@ public class CitizensNPC extends AbstractNPC {
 
         spawned = false;
         save();
+        return true;
     }
 
     @Override
@@ -71,16 +72,16 @@ public class CitizensNPC extends AbstractNPC {
     }
 
     @Override
-    public void spawn(Location loc) {
+    public boolean spawn(Location loc) {
         if (isSpawned()) {
             Messaging.debug("The NPC with the ID '" + getId() + "' is already spawned.");
-            return;
+            return false;
         }
 
         NPCSpawnEvent spawnEvent = new NPCSpawnEvent(this, loc);
         Bukkit.getPluginManager().callEvent(spawnEvent);
         if (spawnEvent.isCancelled())
-            return;
+            return false;
 
         if (mcEntity == null)
             mcEntity = manager.spawn(this, loc);
@@ -92,6 +93,7 @@ public class CitizensNPC extends AbstractNPC {
 
         spawned = true;
         save();
+        return true;
     }
 
     @Override

src/net/citizensnpcs/util/ByIdArray.java

@@ -1,6 +1,7 @@
 package net.citizensnpcs.util;
 
 import java.util.Arrays;
+import java.util.ConcurrentModificationException;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 
@@ -18,7 +19,7 @@ public class ByIdArray<T> implements Iterable<T> {
 
     public ByIdArray(int capacity) {
         if (capacity < 0)
-            throw new IllegalArgumentException("illegal capacity");
+            throw new IllegalArgumentException("Capacity cannot be less than 0.");
         this.capacity = capacity;
         elementData = new Object[capacity];
     }
@@ -81,6 +82,7 @@ public class ByIdArray<T> implements Iterable<T> {
     @Override
     public Iterator<T> iterator() {
         return new Iterator<T>() {
+            private final int expected = ByIdArray.this.modCount;
             private int idx = lowest;
 
             @Override
@@ -91,6 +93,8 @@ public class ByIdArray<T> implements Iterable<T> {
             @Override
             @SuppressWarnings("unchecked")
             public T next() {
+                if (ByIdArray.this.modCount != expected)
+                    throw new ConcurrentModificationException();
                 T next = (T) elementData[idx];
                 if (next == null || idx > highest)
                     throw new NoSuchElementException();