今天主要学习了Object Pascal的面向对象部分：类的定义、继承、多态这些基本操作。
1.Delphi的关键词好麻烦，居然result都没法用，返回值的错误我查找了很久才明白为什么编译器说result重定义。
2.语法结构严谨，比如类定义必须在interface之后，过程/函数的实现必须要分开，而无法写成C++/Java那种inner类定义，写起来难免缚手缚脚。
3.大小写的语法规范很麻烦，像Integer/String这些关键词，我真不知道该不该首字母大写。还有变量的定义，按照“Delphi编码规范”是应该大写，可是这样就需要频繁的使用Shift，还是喜欢Java的那种首字符小写的驼峰式，能够清楚地把函数/过程/变量区分开。
4.fuction/procedure除了返回值又没什么大区别，现在想来真爱死void了。
下面上今天学习的代码，是类的定义、继承、多态这些。
1.类的使用
unit USharp;
{接口定义}
interface
type
{定义类TSharp}
TSharp = class(TObject)
private
FWeight : Double;
procedure SetWeight(Weight : Double);
public
{定义属性Weight}
property Weight : Double read FWeight write SetWeight;
procedure Display();
procedure Draw() ;virtual;
end;
{实现}
implementation
procedure TSharp.SetWeight(Weight : Double);
begin
FWeight := Weight;
end;
procedure TSharp.Display();
begin
{Self.ClassName获取当前类名}
Writeln('Im ', Self.ClassName, ' , my weight is ', FWeight);
end;
{空方法，我不明白虚方法为什么还需要在基类实现…}
procedure TSharp.Draw();
begin
end;
end.
2.类的继承和多态
unit UCircle;
{Circle类模块}
interface
uses
USharp;
type
TCircle = class(TSharp)
private
FR : Double;
procedure SetR (R : Double);
public
property R : Double read FR write SetR;
{重载父类Display方法}
procedure Display();
{重写父类Draw虚方法，关键词override}
procedure Draw(); override;
end;
implementation
procedure TCircle.SetR(R : Double);
begin
FR := R;
end;
procedure TCircle.Display();
begin
Writeln('Im ', Self.ClassName, ' , I am in TCircle.');
end;
procedure TCircle.Draw();
begin
Writeln('Draw a Circle.');
end;
end.
unit USquare;
interface
uses
USharp;
type
{定义类TSharp}
TSquare = class(TSharp)
private
FX : Double;
FY : Double;
procedure SetX(X : Double);
procedure SetY(Y : Double);
public
{定义属性Weight}
property X : Double read FX write SetX;
property Y : Double read FY write SetY;
procedure Display();
{重写父类Draw虚方法，关键词override}
procedure Draw(); override;
end;
{实现}
implementation
procedure TSquare.SetX(X : Double);
begin
FX := X;
end;
procedure TSquare.SetY(Y : Double);
begin
FY := Y;
end;
procedure TSquare.Display();
begin
{Self.ClassName获取当前类名}
Writeln('Im ', Self.ClassName, ' , my x is ', X, ', y is ', Y);
end;
procedure TSquare.Draw();
begin
Writeln('Draw a Square.');
end;
end.
program P2;
{使用类继承和多.pas文件}
{$APPTYPE CONSOLE}
uses
SysUtils,
USharp in 'USharp.pas',
UCircle in 'UCircle.pas',
USquare in 'USquare.pas';
var
Sharp : TSharp;
Circle : TCircle;
Square : TSquare;
{用来进行多态的TSharp}
SharpVirtual : TSharp;
{用来进行类型转换的TSquare}
SquareForAs : TSquare;
begin
Sharp := TSharp.Create();
Sharp.Weight := 1.3;
Sharp.Display();
Circle := TCircle.Create();
Circle.Weight := 2.2;
Circle.R := 1.2;
Circle.Display();
Square := TSquare.Create();
Square.Weight := 4.5;
Square.X := 2;
Square.Y := 3;
Square.Display();
{将变量分别指向TCicle和TSquare，运行Draw实现多态}
SharpVirtual := TCircle.Create();
SharpVirtual.Draw();
SharpVirtual := TSquare.Create();
SharpVirtual.Draw();
{is操作符}
Writeln(Circle is TCircle);
Writeln(SharpVirtual is TCircle);
Writeln(SharpVirtual is TSquare);
{as类转换操作符}
SquareForAs := SharpVirtual as TSquare;
SquareForAs.Draw;
Readln;
end.
本来准备入手VCL，结果事情太多，下午党员会议，晚上我又提前1个月过生日请朋友吃饭唱歌，耽误了“`
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原文链接: http://dddspace.com/2009/12/delphi-study-notes-04.html
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