@Override
	protected int addChildToTask (Task<E> child) {
		if (this.rootTask != null) throw new IllegalStateException("A behavior tree cannot have more than one root task");
		this.rootTask = child;
		return 0;
	}
@ Override protected int addChildToTask ( Task < E > child ) { if ( this . rootTask != null ) throw new IllegalStateException ( "A behavior tree cannot have more than one root task" ) ; this . rootTask = child ; return 0 ; }
This method will add a child, namely the root, to this behavior tree.

@param child the root task to add
@return the index where the root task has been added (always 0).
@throws IllegalStateException if the root task is already set.