Thread-safe list?

sig/App.java

@@ -292,7 +292,7 @@ class Server
         }
     }
 
-    Collection<String>commandQueue=Collections.synchronizedCollection(new ArrayList<>());
+    List<String>commandQueue=Collections.synchronizedList(new ArrayList<>());
  
     // constructor with port
     public Server(int port)
@@ -454,6 +454,7 @@ class Server
                                 }
                             }
                         }
+                        commandQueue.clear();
 
                         if (queueUpSprint&&nextActionTimer==0){
                             PressKey(KeyEvent.VK_N);