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objs.pas：源码内容

							unit objs;
interface
uses classes,strutils,sysutils,Variants,Contnrs;
type
  //去掉了TOrderedList的Create和Destroy方法。不先创建FList。
  //从而，可以在子类中子类化FList的类型。
  TCustomOrderList=class(TObject)
  private
    FList: TList;
  protected
    procedure PushItem(AItem: Pointer); virtual; abstract;
    function PopItem: Pointer; virtual;
    function PeekItem: Pointer; virtual;
    property List: TList read FList Write FList;
  public
    function Count: Integer;
    function AtLeast(ACount: Integer): Boolean;
    function Push(AItem: Pointer): Pointer;
    function Pop: Pointer;
    function Peek: Pointer;
  end;
  //TCustomObjectList=class
  TCustomQueue=class(TCustomOrderList)
  protected
    procedure PushItem(AItem: Pointer); override;
  end;
implementation
{ TCustomOrderList }
function TCustomOrderList.AtLeast(ACount: integer): boolean;
begin
  Result := List.Count >= ACount;
end;
function TCustomOrderList.Peek: Pointer;
begin
  Result := PeekItem;
end;
function TCustomOrderList.Pop: Pointer;
begin
  Result := PopItem;
end;
function TCustomOrderList.Push(AItem: Pointer): Pointer;
begin
  PushItem(AItem);
  Result := AItem;
end;
function TCustomOrderList.Count: Integer;
begin
  Result := List.Count;
end;
function TCustomOrderList.PeekItem: Pointer;
begin
  Result := List[List.Count-1];
end;
function TCustomOrderList.PopItem: Pointer;
begin
  Result := PeekItem;
  List.Delete(List.Count-1);
end;
{ TCustomQueue }
procedure TCustomQueue.PushItem(AItem: Pointer);
begin
  List.Insert(0, AItem);
end;
end.

						