自定义异常类实例

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Label4: TLabel;
    Edit1: TEdit;
    Edit2: TEdit;
    Edit3: TEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

type
  Eyearmeanerror = class(exception)                                  //自定义的异常类
    function transformyer(yearstr: string): string;
  end;

function Eyearmeanerror.transformyer(yearstr: string): string;
begin
  if strtoint(yearstr) > strtoint(copy(datetostr(date),0,4)) then
    begin
      showmessage('目前最晚只到' + #13 + '公元' + copy((datetostr(date)),0,4) + '年');
      yearstr := copy(datetostr(date),0,4);
    end
  else
    begin
      if strtoint(yearstr) <= (strtoint(copy(datetostr(date),0,4)) - 1911) then
        begin
          showmessage('使用的是"公元"年');
          yearstr := inttostr(strtoint(yearstr) + 1911);
        end
      else
        yearstr := '';
    end;
    result := yearstr;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  thedate: tdatetime;
begin
  try
    thedate := strtodate(edit1.Text + '-' + edit2.Text + '-' + edit3.Text);
    if (length(edit1.Text) < 4) or (strtoint(edit1.Text) > strtoint(copy(datetostr(date),0,4))) then
      raise eyearmeanerror.Create('日期有误');
        showmessage('你的生日是公元' + datetostr(thedate));
      except
        on e: econverterror do                                       //捕捉内建的Econverterror异常
          messagedlg('输入的不是数字' + #13 + '或日期不符合事实' + #13 + '年不可以大于9999！',mterror,[mbok],0);
        on e: eyearmeanerror do                                      //捕捉自定义的Eyearmeanerror异常
          begin
            messagedlg(e.Message,mterror,[mbok],0);
            edit1.Text := e.transformyer(edit1.Text);
          end;
        else
          raise;                                                     //产生其他异常
  end;
end;

end.