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五、类是一种对数据和操作高度的封装机制 1)数据封装 unit Unit2; interface type TEmployee = class; private FName: String; public Constructor Create; function GetName: String; procedure SetName(AName: String); end; implementation constructor TEmployee.Create; begin FName:= 'Xumenger'; end; function TEmployee.GetName: String; begin Result:= FName; end; procedure TEmployee.SetName(AName: String); begin FName:= AName; end; end. 如上面的代码,我们就用了一个过程SetName和一个函数GetName对私有变量FName进行完全的封装。我们要对FName进行操作就只要这样: uses Unit2; procedure TForm1.Button1Click(Sender: TObject); var AEmployee: TEmployee; begin AEmployee:= TEmployee.Create; AEmployee.SetName('Joker'); MessageBox(Handle, PChar(AEmployee.GetName), 'Employee' 0); AEmployee.Free; end;
2)操作封装 unit Unit2; interface type TDivision = class public function GetDiv(Num1, Num2: Double): Double; overload; function GetDiv(Num1, Num2: Integer): Integer; overload; end; implementation function TDivision.GetDiv(Num1, Num2: Double): Double; begin try Result:= Num1/Num2; except Resulr:=0; //提供弹性处理机制,处理除数为0的情况 end; end; function TDivision.GetDiv(Num1, Num2: Integer): Integer; begin try Result:= Num1 div Num2; //注意Double的除法和Integer的除法的操作符的差别 except Resulr:=0; //提供弹性处理机制,处理除数为0的情况 end; end; 如上的代码通过类的多态性机制把除法分别处理成整数型和非整数型,又通过异常处理去处理除数为0的异常,从而保证操作的安全性,在调用的时候,就可以这样 uses Unit2; procedure TForm1.ButtonClick(Sender: TObject); var Division: TDivision; IValue: Integer; FValue: Double: begin Division:= TDivision.Create; IValue:= Division.GetDiv(1, 2); FValue:= Division.GetDiv(1.0, 2); IValue:= Division.GetDiv(1, 0); FValue:= Division.GetDiv(1.0, 0); Division.Free; end;
六、类是一种代码重用机制 比方在 五 中我们想对这个类加上一个GetAdd函数来做加法运算就可以用类的继承,如 unit Unit2; interface type TDivision = class public function GetDiv(Num1, Num2: Double): Double; overload; function GetDiv(Num1, Num2: Integer): Integer; overload; end; type TOperation = class(TDivision) public function GetAdd(Num1, Num2: Double): Double; end; implementation { Division } function TDivision.GetDiv(Num1, Num2: Double): Double; begin try Result:=Num1/Num2; except Result:=0; end; end; function TDivision.GetDiv(Num1, Num2: integer): integer; begin try Result:=Num1 div Num2; except Result:=0; end; end; { TOperation } function TOperation.GetAdd(Num1, Num2: Double): Double; begin Result:=Num1+Num2; end; end. 这里我们从TDivision继承了一个子类TOperation。TOperation就可以既有TDivision公有方法GetDiv,又可以有自己的独特的方法GetAdd |
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