create or replace type X1 as object
(
  attr_X integer,
  member function GetX return integer
)
/

create or replace type body X1 is
 
  member function GetX return integer is
  begin
    return attr_X;
  end;
  
end;
/

create or replace type Y1 as object
(
  obj_X X1,
  
  constructor function Y1 return self as result,
  
  member function GetObjX(SELF IN OUT NOCOPY Y1) return X1
)
/

create or replace type body Y1 is
 
  constructor function Y1 return self as result is
  begin
    return;
  end;

  member function GetObjX(SELF IN OUT NOCOPY Y1) return X1 is
  begin
    if obj_X is null then
      obj_X := X1(5); 
    end if;
    
    return obj_X;
  end;
  
end;
/

create or replace type Z1 as object
(
  obj_Y Y1,
  
  constructor function Z1 return self as result,
  
  member function GetObjY(SELF IN OUT NOCOPY Z1) return Y1
)
/

create or replace type body Z1 is
 
  constructor function Z1 return self as result is
  begin
    return;
  end;

  member function GetObjY(SELF IN OUT NOCOPY Z1) return Y1 is
  begin
    if obj_Y is null then
      obj_Y := Y1(); 
    end if;
    
    return obj_Y;
  end;
  
end;
/


declare
  y Y1;
  z Z1;
  i integer;
begin
  -- example 1
  y := Y1();
  i := y.GetObjX().GetX;  
  
  -- example 2
  z := Z1();
  i := z.GetObjY().GetObjX().GetX;
  
  dbms_output.put_line(to_char(i));
end;
/