JavaECS-Docs/docs/entity/Entity.md

*| [JavaECS](../../README.md) | [docs](../overview.md) | [entity](./dir.md) | Entity[]().md*
# Entity

### Contents
[About](#about)

[Usage](#usage)

[Notes](#notes)

## About
An 'entity' is a unique ID.

For most implementations, it makes sense to use a simple integer value to represent an entity. As each entity must have a unique 
ID/number, we can use a First-In-First-Out (FIFO) data structure, such as a Queue, to efficiently retrieve the next unassigned ID.

<br>

**This ID represents a specific instance of a game object**

e.g. character, vehicle, effect etc.

___An entity contains no further data.___

In order to be useful, its identifier must be registered to one or more [components](../component/Component.md).


Entities are also initialised with a Java [BitSet](https://docs.oracle.com/javase/7/docs/api/java/util/BitSet.html). Each bit represents the index of a component, to determine which component an entity is registered to.

## Usage
*some specific usage info here*
``` java
void todo();
```

## Notes
* The only requirement for a Entity is that it has a unique ID. A more advanced [entity manager](../manager/EntityManager.md) could implement an ID system with ID regions, or using named IDs. 
Another approach could be to use the first byte as a grouping, in a similar way to how Bethesda Softworks' Skyrim utilises the first byte as a mod index
* The maximum number of entities is limited by the size of the container used to store it. E.g., for a 32-bit unsigned integer, there are ~4.3 billion ID's available. But keep in mind that such a large amount of IDs will take significant time for each system to consider.