TThread是抽象的。为什么不能创建TThread实例

Question

   为什么说啊
这是源码:            TThread = class       //--------------------------------
  private
{$IFDEF MSWINDOWS}
    FHandle: THandle;
    FThreadID: THandle;
{$ENDIF}
{$IFDEF LINUX}
    // ** FThreadID is not THandle in Linux **
    FThreadID: Cardinal;
    FCreateSuspendedSem: TSemaphore;
    FInitialSuspendDone: Boolean;
{$ENDIF}
    FCreateSuspended: Boolean;
    FTerminated: Boolean;
    FSuspended: Boolean;
    FFreeOnTerminate: Boolean;
    FFinished: Boolean;
    FReturnValue: Integer;
    FOnTerminate: TNotifyEvent;
    FSynchronize: TSynchronizeRecord;
    FFatalException: TObject;
    procedure CallOnTerminate;
    class procedure Synchronize(ASyncRec: PSynchronizeRecord); overload;
{$IFDEF MSWINDOWS}
    function GetPriority: TThreadPriority;
    procedure SetPriority(Value: TThreadPriority);
{$ENDIF}
{$IFDEF LINUX}
    // ** Priority is an Integer value in Linux
    function GetPriority: Integer;
    procedure SetPriority(Value: Integer);
    function GetPolicy: Integer;
    procedure SetPolicy(Value: Integer);
{$ENDIF}
    procedure SetSuspended(Value: Boolean);
  protected
    procedure CheckThreadError(ErrCode: Integer); overload;
    procedure CheckThreadError(Success: Boolean); overload;
    procedure DoTerminate; virtual;
    procedure Execute; virtual; abstract;
    procedure Synchronize(Method: TThreadMethod); overload;
    property ReturnValue: Integer read FReturnValue write FReturnValue;
    property Terminated: Boolean read FTerminated;
  public
    constructor Create(CreateSuspended: Boolean);
    destructor Destroy; override;
    procedure AfterConstruction; override;
    procedure Resume;
    procedure Suspend;
    procedure Terminate;
    function WaitFor: LongWord;
    class procedure Synchronize(AThread: TThread; AMethod: TThreadMethod); overload;
    class procedure StaticSynchronize(AThread: TThread; AMethod: TThreadMethod);
    property FatalException: TObject read FFatalException;
    property FreeOnTerminate: Boolean read FFreeOnTerminate write FFreeOnTerminate;
{$IFDEF MSWINDOWS}
    property Handle: THandle read FHandle;
    property Priority: TThreadPriority read GetPriority write SetPriority;
{$ENDIF}
{$IFDEF LINUX}
    // ** Priority is an Integer **
    property Priority: Integer read GetPriority write SetPriority;
    property Policy: Integer read GetPolicy write SetPolicy;
{$ENDIF}
    property Suspended: Boolean read FSuspended write SetSuspended;
{$IFDEF MSWINDOWS}
    property ThreadID: THandle read FThreadID;
{$ENDIF}
{$IFDEF LINUX}
    // ** ThreadId is Cardinal **
    property ThreadID: Cardinal read FThreadID;
{$ENDIF}
    property OnTerminate: TNotifyEvent read FOnTerminate write FOnTerminate;
  end;

Answer 1

我觉得是因为 tthread 类没有实现 execute 方法不知道对不对，呵呵

Answer 2

你既然知道是抽象类，就不难理解了。一个抽象的概念而已，没任何实体。你说怎么去创建实例。
呵呵。OOP的工夫还不到家哦！

Answer 3

修正：
delphi中抽象类可以创建实例，但是其抽象方法不可用
与java不同

Answer 4

To  meiqingsong(阿飛):
         老大一语惊人，能否举例吗?

Answer 5

unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Grids, StdCtrls, DB, ADODB;type
  TA = class(TObject)
    private
      a: Integer;
    public
      function GetA():Integer;
      procedure setA(value: Integer);
      function GetN():Integer; virtual; Abstract;
  end;
  TForm1 = class(TForm)
    Button1: TButton;
    ADOQuery1: TADOQuery;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);
var
  a: TA;
begin
  a := TA.Create;
  a.setA(136);
  ShowMessage(IntToStr(a.GetA));
end;
{ Abs }{ TA }function TA.GetA: Integer;
begin
  Result := a;
end;procedure TA.setA(value: Integer);
begin
  a := value;
end;end.

Answer 6

meiqingsong(阿飛):
         飞哥，如果只是只是为了给派生类实现多态性用的，起不是成了一个鸡肋啊,
         飞哥还有何高见啊

Answer 7

delphi中抽象类可以创建实例，但是其抽象方法不可用==============================正解

Answer 8

飞哥，非常感谢你!      http://community.csdn.net/Expert/topic/3560/3560228.xml?temp=.4488336