Delphi語言學習7-類和對象

1.類的聲明格式

type
   className = class [abstract | sealed] (ancestorClass)
      memberList
   end;

2.類的聲明和使用

//定義
 type TMemoryStream = class(TCustomMemoryStream)
            private
              FCapacity: Longint;
              procedure SetCapacity(NewCapacity: Longint);
            protected
              function Realloc(var NewCapacity: Longint): Pointer; virtual;
              property Capacity: Longint read FCapacity write SetCapacity;
            public
              destructor Destroy; override;
              procedure Clear;
              procedure LoadFromStream(Stream: TStream);
              procedure LoadFromFile(const FileName: string);
              procedure SetSize(NewSize: Longint); override;
              function Write(const Buffer; Count: Longint): Longint; override;
          end;
//使用
 var stream: TMemoryStream;
     stream := TMemoryStream.Create;

3.類的繼承

//繼承一個類
type TSomeControl = class(TControl);
//根類 TObject
type TMyClass = class
     ...
     end;
//等價於
type TMyClass = class(TObject)
     ...
     end;

4.基類和子類

type
     TFigure = class(TObject);
     TRectangle = class(TFigure);
     TSquare = class(TRectangle);
var
     Fig: TFigure;
//the variable Fig can be assigned values of type TFigure, TRectangle, and TSquare.

5.獲取對象類型

type objectTypeName = object (ancestorObjectType)
        memberList
     end;

6.類的關聯

type
      TFigure = class;   // forward declaration
      TDrawing = class
         Figure: TFigure;
        ...
      end;
      TFigure = class   // defining declaration
         Drawing: TDrawing;
        ...
      end;