Improved root data types

javaecs/src/main/java/nz/ac/massey/programming_project_159333_s1_2021/ECS.java

@@ -3,17 +3,41 @@
  * 
  * Contributors:
  * Brychan Dempsey - brychand@hotmail.com
+ * 
+ * References:
+ * https://code.austinmorlan.com/austin/ecs - 'A simple C++ Entity Component System' - released under MIT licence
+ *  
  */
 
 import java.util.*;
 
 public class ECS {
-    // Entities in an ECS are just a unique integer
+    // As mentioned by Austin Morlan, a queue is a better choice of data structure for the entity list
-    List<Integer> entities = new ArrayList<>();
+    // - it allows the first element to be efficiently popped from the list
+    Queue<Integer> unusedEntities = new ArrayList<>();
+
+    // As the entity subscribes (or does not) to a component, we can use a boolean state to represent the subscription
+    // If we instead store the list of indicies the component is subscribed to, we would use significantly more 
+    // memory space due to the components being defined as a 32-bit integer.
+    // In a BitSet, each bit is a flag. Therefore we can represent subscription to the first 32 components in the
+    // same space as one as a 32-bit int.
+    //
+    // This list therefore uses the index of the BitSet as its reference to the entity.
+    List<BitSet> entityRegistrations = new ArrayList<>();
+
+    // Each component can be assigned to every possible entity. There is a reasonably unlimited number of possible components;
+    // so therefore we get an array of arrays containing all of a component's data allocations.
+    // Access is in [componentType][entityNumber] format; getting the data from a subscribed entity is performed like so:
+    // (<datatype>)componentDataArrays.get(ComponentIndex).get(Entity);
+    // Unfortunately, given Java's constraints on dynamic typing (run-time type determination), the returned data must be
+    // explicitly cast. Therefore, all components must implement the IComponent interface - which mandates the getType()
+    // function
+    List<List<Object>> componentDataArrays = new ArrayList<>();
+
     // Components are either primitive types or class/struct definitions, with an additional list associating
     // the entities the component is assigned to
     List<Object> components = new ArrayList<>();
-    List<List<Object>> componentAssociations = new ArrayList<>();
+    
     // Systems are user-defined functions that are called by the game engine, usually at a regular interval such 
     // as between every render frame. It must be able to find all instances of a specific component, in order
     // to update/read its data. A component