declare 
ct integer;
type arr is varray(12) of varchar2(8);
months arr := arr('201901','201902','201903','201904','201905'); 
begin
  
  dbms_output.put_line(months.count);--实际数量
  dbms_output.put_line(months.limit);--容量
  
  for k in 1..months.count loop
     dbms_output.put_line(months(k));
  end loop;
  
  for k in months.first..months.last loop
     dbms_output.put_line(months(k));
  end loop;
  
  ct :=1;
  while ct is not null loop
    dbms_output.put_line(months(ct));
    ct := months.next(ct);
  end loop;
  
  /*
  --下标超出数量
  dbms_output.put_line(months(6));
  months(6) := '201906';
  months(7) := '201907';
  months(8) := '201908';
  */
  
  months.extend(3);
  months(6) := '201906';
  months(7) := '201907';
  months(8) := '201908';
  dbms_output.put_line(months.count);
  
  months.trim();--删除最后一个元素
  months.trim(months.count);
  months.delete();
  
  for k in 1..months.count loop
     dbms_output.put_line(months(k));
  end loop;
  
end;