edit1'in text değerini object inspector'dan silin.
 
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
  if (not (key='a')) and (length(edit1.Text)=0) then begin key:='a'; end;
  if (not (key='r')) and (length(edit1.Text)=1) then begin key:='r'; end;
  if (not (key='a')) and (length(edit1.Text)=2) then begin key:='a'; end;
  if (not (key='b')) and (length(edit1.Text)=3) then begin key:='b'; end;
  if (not (key='a')) and (length(edit1.Text)=4) then begin key:='a'; end;
 
  if length(edit1.Text)>4 then
  begin
    edit1.Clear;
    key:='a';
  end;
end;
 
 
 yada
  
  
{global değişken}
a:string='yazdırılmak İstenen MeTin......';
 
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
var
 au,i:integer;
begin
 au:=length(a);
 for i:=1 to au do
   begin
     if (not (key=a[i])) and (length(edit1.Text)=i-1) then key:=a[i];
   end;
 if length(edit1.Text)>length(a)-1 then
 begin
   edit1.Clear;
   key:=a[1];
 end;