private static ArrayList<ConstraintWidgetContainer> gatherContainers(ConstraintWidgetContainer container){
  ArrayList<ConstraintWidgetContainer> containers=new ArrayList<>();
  for (  ConstraintWidget widget : container.getChildren()) {
    if (widget instanceof ConstraintWidgetContainer) {
      containers.add((ConstraintWidgetContainer)widget);
    }
  }
  return containers;
}

private static ArrayList < ConstraintWidgetContainer > gatherContainers ( ConstraintWidgetContainer container ) { ArrayList < ConstraintWidgetContainer > containers = new ArrayList < > ( ) ; for ( ConstraintWidget widget : container . getChildren ( ) ) { if ( widget instanceof ConstraintWidgetContainer ) { containers . add ( ( ConstraintWidgetContainer ) widget ) ; } } return containers ; }
gather a list of containers that are children of the given container
