Doubts in constructer and create method during factory registration

UVM
3

In reply to chrisspear:
When I am executing the hello world program by doulos academy


interface dut_if;

endinterface


module dut(dut_if dif);

endmodule

`include "uvm_macros.svh"

package my_pkg;

  import uvm_pkg::*;

  class my_env extends uvm_env;

    `uvm_component_utils(my_env)
    
    function new(string name, uvm_component parent);
      super.new(name, parent);
    endfunction
 
  endclass: my_env
  
  
  class my_test extends uvm_test;
  
    `uvm_component_utils(my_test)
    
    my_env m_env;
    
    function new(string name, uvm_component parent);
      super.new(name, parent);
    endfunction
    
    function void build_phase(uvm_phase phase);
      m_env = my_env::type_id::create("m_env", this);
    endfunction
    
    task run_phase(uvm_phase phase);
      phase.raise_objection(this);
      #10;
      `uvm_info("TEST", "Hello Teja", UVM_MEDIUM)
      phase.drop_objection(this);
    endtask
     
  endclass: my_test
  
  
endpackage: my_pkg


module top;

  import uvm_pkg::*;
  import my_pkg::*;
  
  dut_if dut_if1 ();
  
  dut    dut1 ( .dif(dut_if1) );

  initial
  begin
    run_test();
  end

endmodule: top       


class driverB #(type T=uvm_object) extends uvm_driver;

  // parameterized classes must use the _param_utils version
  `uvm_component_param_utils(driverB #(T))

  // our packet type; this can be overridden via the factory
  T pkt;

  // standard component constructor
  function new(string name, uvm_component parent=null);
    super.new(name,parent);
  endfunction

  // get_type_name not implemented by macro for parameterized classes
  const static string type_name = {"driverB #(",T::type_name,")"};
  virtual function string get_type_name();
    return type_name;
  endfunction

  // using the factory allows pkt overrides from outside the class
  virtual function void build_phase(uvm_phase phase);
    pkt = packet::type_id::create("pkt",this);
  endfunction

  // print the packet so we can confirm its type when printing
  virtual function void do_print(uvm_printer printer);
    printer.print_object("pkt",pkt);
  endfunction

endclass

If you will see above two programs in one program(constructor) is not using anything and one program(constructor) is using null. If you come to create method I just want to know what will happen if we use null and this.