@startuml

package RealWorldExample{
  abstract DrawingElement {
    # name: string
    + DrawingElement(name: string)

    + virutal Add(DrawingElement)
    + virutal Remove(DrawingElement)
    + virutal Display(indent: int)
  }

  class PrimitiveElement extends DrawingElement{
    + PrimitiveElement(name: string)
    + Add(DrawingElement)
    + Remove(DrawingElement)
    + Display(indent: int)
  }
  
  class CompositeElement extends DrawingElement{
    + CompositeElement(name: string)

    - elements: List<DrawingElement>

    + Add(DrawingElement)
    + Remove(DrawingElement)
    + Display(indent: int)
  }
  class Program
  Program -l-> DrawingElement: "    "
  CompositeElement "1" o-l--- "*" PrimitiveElement: "     "
}
@enduml