*| [JavaECS](../../README.md) | [docs](../overview.md) | [system](./dir.md) | SystemManager[]().md*
# System Manager
| **In this Section** |
|-|
| [About](#about) |
| [Implementation](#implementation) |
| [Constructors](#constructors) |
| [Methods](#methods) |
| [Fields](#fields) |
| [Examples](#examples)|
| [Notes](#notes)|

## About
The system manager class controls references to the systems.

## Implementation
Before attempting to use a system, it must be registered.

Registration requires a call to `registerSystem(String systemName, ECSSystem system)`, with params of the `String name` and a object reference of the [ECSSystem](./ECSSystem.md). Using the object reference, a system can be invoked at any time.

## Constructors
Default constructor
``` java
public SystemManager(){}
```
<br>

## Methods

### entityDestroyed
``` java
public void entityDestroyed(int entity);
```
Removes the specified entity from every system, if it was associated

<br>

### entitySignatureChanged
``` java
public void entitySignatureChanged(int entity, BitSet entitySignature);
```
Checks the entity's new signature against the current registrations. Registers the entity if it wasn't previously registered, or removes it if it is no longer registered.

<br>

### registerSystem
``` java
public boolean registerSystem(String systemName, ECSSystem system);
```
Registers the specified system name and system reference to this manager.

*adds a `systemName:system` pair to [systems](#systems)*

*and a `systemName:new BitSet()` pair to [signatures](#signatures)*

<br>

### setSignature
``` java
public void setSignature(String system, BitSet registrations);
```
Sets the required signature of the `system`

<br>

## Fields
### signatures
``` java
Map<String, BitSet> signatures = new HashMap<>();
```

<br>

### systems
``` java
Map<String, ECSSystem> systems = new HashMap<>();
```

<br>