我的一个visitor实作
　

---

public interface Visitable
{
void accept(Visitor visitor);
}
public interface Visitor
{
void visit(Visitable visitable);
}


public class VisitableA implements Visitable
{
public String Call(){
return "AAA";
}
public void accept(Visitor visitor) {
visitor.visit(this);
}
}


public class VisitorA implements Visitor
{ public void visit(Visitable visitable) {
if (visitable instanceof VisitableA)
{
System.out.println(((VisitableA)visitable).Call());
}
}

}


public class Client{
public static void main(String args[])
{
Visitor visitor=new VisitorA();
Visitable visitable=new VisitableA();
visitable.accept(visitor);
}
}

 delphi版本的
　

---

unit UVisitor;

interface

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

type

TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

type
TVisitor=class;
TVisitable=class
procedure accept(visitor:TVisitor);virtual;abstract;
end;
TVisitor=class
procedure visit(visitable:TVisitable);virtual;abstract;
end;
TVisitableA=class(TVisitable)
public
procedure accept(visitor:TVisitor);override;
function Call():string;
end;
TVisitorA=class(TVisitor)
public
procedure visit(visitable:TVisitable);override;
end;


{$R *.dfm}

{ TVisitableA }

procedure TVisitableA.accept(visitor: TVisitor);
begin
inherited;
visitor.visit(self);
end;

function TVisitableA.Call: string;
begin
Result:='AAA';
end;

{ TVisitorA }

procedure TVisitorA.visit(visitable: TVisitable);
begin
inherited;
if visitable is TVisitableA then
showmessage(TVisitableA(visitable).Call);
end;

procedure TForm1.Button1Click(Sender: TObject);
var
v:TVisitor;
vb:TVisitable;
begin
v:=TVisitorA.Create;
vb:=TVisitableA.Create;
vb.accept(v);
v.Free;
vb.Free;
end;

end.

 vb.net版本的
　

---

Public Class Form1
Inherits System.Windows.Forms.Form

Public MustInherit Class Visitor
Public MustOverride Sub visit(ByRef vb As Visitable)
End Class

Public MustInherit Class Visitable
Public MustOverride Sub accept(ByRef v As Visitor)
End Class

Public Class VisitorA
Inherits Visitor
Public Overrides Sub visit(ByRef vb As Visitable)
If vb.GetType Is GetType(VisitableA) Then
MessageBox.Show(CType(vb, VisitableA).CallOp, "")
End If
End Sub
End Class

Public Class VisitableA
Inherits Visitable
Public Function CallOp() As String
Return "AAA"
End Function
Public Overrides Sub accept(ByRef v As Visitor)
v.visit(Me)
End Sub
End Class



Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim vb As Visitable
Dim v As Visitor
vb = New VisitableA()
v = New VisitorA()
vb.accept(v)
vb = Nothing
v = Nothing
End Sub
End Class