*| [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.

See [SystemManager.java](/BrychanD/JavaECS/src/branch/master/javaecs/src/main/java/nz/ac/massey/javaecs/SystemManager.java) for the full implementation.

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

<br>

## Methods

### entityDestroyed
``` java
protected void entityDestroyed(int entity);
```
Signals the SystemManager that an entity was destroyed. Removes the entity from each system's tracked entities

<br>

### entitySignatureChanged
``` java
protected void entityRegistrationsChanged(int entity, BitSet entityRegistrations);
```
Signals the SystemManager that an entity had its registrations changed; iterates through each system validating the entities list

<br>

### registerSystem
``` java
protected boolean registerSystem(Type systemType, ECSSystem system);
```
Registers the specified system name and system reference to this manager.

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

*adds a `systemType:new BitSet()` pair to [registrationSignatures](#registrationSignatures)*

<br>

### setSignature
``` java
protected void setRegistrationSignature(Type systemType, BitSet registrations);
```
Sets the registrations the system requires

<br>

## Fields
### registrationSignatures
``` java
private Map<Type, BitSet> registrationSignatures = new HashMap<>()
```
The mapped list of required registrations

<br>

### systems
``` java
private Map<Type, ECSSystem> systems = new HashMap<>();
```
The mapped list of system instances

<br>