# DefaultWorldInitialization

> Utilities to help initialize the default ECS World.

## Definition

* **Type:** Class
* **Namespace:** [Unity.Entities](/engine/7000.0/script-reference/unity/entities.md)
* **Assembly:** UnityEngine.EntitiesModule

```csharp
public static class DefaultWorldInitialization
```

## Static Methods

| Method                                                                                                                                              | Description                                                                                                                                                                                                                                                                     |
| --------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| [AddSystemsToRootLevelSystemGroups](/engine/7000.0/script-reference/unity/entities/defaultworldinitialization/addsystemstorootlevelsystemgroups.md) | Adds the collection of systems to the world by injecting them into the root level system groups (InitializationSystemGroup, SimulationSystemGroup and PresentationSystemGroup). Prefer the version that takes SystemTypeIndex's as an argument to avoid unnecessary reflection. |
| [GetAllSystems](/engine/7000.0/script-reference/unity/entities/defaultworldinitialization/getallsystems.md)                                         | Calculates a list of all systems filtered with WorldSystemFilterFlags, \[DisableAutoCreation] etc. Prefer GetAllSystemTypeIndices where possible to avoid extra reflection.                                                                                                     |
| [GetAllSystemTypeIndices](/engine/7000.0/script-reference/unity/entities/defaultworldinitialization/getallsystemtypeindices.md)                     | Calculates a list of all systems filtered with WorldSystemFilterFlags, \[DisableAutoCreation] etc. Prefer this over GetAllSystems if possible, to avoid extra reflection usage.                                                                                                 |
| [Initialize](/engine/7000.0/script-reference/unity/entities/defaultworldinitialization/initialize.md)                                               | Initializes the default world or runs ICustomBootstrap if one is available.                                                                                                                                                                                                     |