*| [JavaECS](../README.md) | [docs](./overview.md) | implementation[]().md*
# Implementation
### Contents
[Steps](#steps)

[Example](#example)

## Steps
1. In the application's setup function, create an instance of `ECS`, with a specified maximum number of entity entries.
2. Define the component classes, (or associate the primitive types) and register the components.
3. Define the systems that interact with the components and register them
4. Run the game.

## Example
``` java
public static void main(){
    ECS gameEngine = new ECS(100);
    // Register the components, with a parameterised type
    gameEngine.registerComponent<coord>(coord.class.getName());
    gameEngine.registerComponent<ridgidBody>(ridgidbody.class.getName());
    // Register the system to run on the component
    gameEngine.registerSystem("ApplyGravitySystem", () -> {
        List<Integer> relevantEntities = gameEngine.getEntitiesWithComponent(ridgidBody.class.getName());
        for (Integer entity : relevantEntities) {
            coord c = (coord)gameEngine.getComponent(entity, coord.class.getName());
            ridgidBody r = (ridgidBody)gameEngine.getComponent(entity, ridgidBody.class.getName());
            c.y -= r.gravity;
        }
    });
    // Create an acutal game object
    int someEntity = gameEngine.createEntity();
    // Assign components to the new game object
    gameEngine.addComponent(someEntity, coord.class.getName(), new coord());
    gameEngine.addComponent(someEntity, ridgidBody.class.getName(), new ridgidBody());
    // Finally, enter into the game loop
    gameEngine.loop();

}

class coord{
    double x = 0.0;
    double y = 0.0;
}

class ridgidBody{
    double gravity = -9.81; // has a default value, unless overridden in the constructor
    ridgidBody(){}
    ridgidBody(double gravity){
        this.gravity = gravity;
    }
}
```



### See also:
[entity](./entity/entity.md)

[component](./component/component.md)

[system](./system/system.md)