Delphi語言學習7-類和對象(2)

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;