public class Attribute {
    private Cell parent;
 
    public Attribute(Cell parent) {
      this.parent = parent;
    }
  }
 
  public class Cell {
    private List attributes;
 
    public Cell() {
      attributes = new ArrayList();
    }
 
    public void addAttribute() {
      Attribute toAdd = new Attribute(this);
      attributes.add(toAdd);
    }
  }