Delphi 设计模式：《HeadFirst设计模式》Delphi7代码---迭代器模式之DinerMenu[转]

容器的主要职责有两个：存放元素和浏览元素。根据单一职责原则（SRP）要将二者分开，于是将浏览功能打包封装就有了迭代器。

用迭代器封装对动态数组的遍历：

{《HeadFirst设计模式》之迭代器模式 }
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{ 容器中的元素类 }
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{ 编译工具：Delphi7.0 }
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{ E-Mail ：guzh-0417@163.com }
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unit uItem;
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interface
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type
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TMenuItem = class(TObject)
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private
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FName: String;
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FDescription: String;
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FVegetarian : Boolean;
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FPrice: Double;
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public
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constructor Create(aName, aDescription: String;
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aVegetarian : Boolean;
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aPrice: Double);
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function GetName: String;
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function GetDescription: String;
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function GetPrice: Double;
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function IsVegetarian: Boolean;
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end;
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implementation
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{ TMenuItem }
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constructor TMenuItem.Create(aName, aDescription: String;
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aVegetarian: Boolean;
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aPrice: Double);
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begin
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FName := aName;
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FDescription := aDescription;
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FVegetarian := aVegetarian;
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FPrice := aPrice;
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end;
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function TMenuItem.GetDescription: String;
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begin
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Result := FDescription;
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end;
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function TMenuItem.GetName: String;
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begin
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Result := FName;
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end;
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function TMenuItem.GetPrice: Double;
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begin
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Result := FPrice;
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end;
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function TMenuItem.IsVegetarian: Boolean;
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begin
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Result := FVegetarian;
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end;
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end.

{《HeadFirst设计模式》之迭代器模式 }
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{ 迭代器：封装对容器的遍历 }
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{ 编译工具：Delphi7.0 }
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{ E-Mail ：guzh-0417@163.com }
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unit uIterator;
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interface
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uses
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uItem;
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type
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TMenuItems = array of TMenuItem;
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TIterator = class(TObject)
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public
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function HasNext: Boolean; virtual; abstract;
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function Next : TObject; virtual; abstract;
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end;
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TDinerMenuIterator = class(TIterator)
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private
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FMenuItem : TMenuItem;
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FMenuItems: TMenuItems;
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FPosition : Integer;
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public
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constructor Create(MenuItems: TMenuItems);
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function HasNext: Boolean; override;
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function Next : TObject; override;
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end;
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implementation
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{ TDinerMenuIterator }
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constructor TDinerMenuIterator.Create(MenuItems: TMenuItems);
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begin
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FMenuItems := MenuItems;
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end;
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function TDinerMenuIterator.HasNext: Boolean;
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begin
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if (FPosition < Length(FMenuItems)) and (FMenuItems[FPosition] <> nil) then
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Result := True
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else
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Result := False;
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end;
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function TDinerMenuIterator.Next: TObject;
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begin
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FMenuItem := FMenuItems[FPosition];
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FPosition := FPosition + 1 ;
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Result := FMenuItem;
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end;
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end.

{《HeadFirst设计模式》之迭代器模式 }
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{ 容器类及其用户： Waitress }
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{ 编译工具：Delphi7.0 }
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{ E-Mail ：guzh-0417@163.com }
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unit uAggregate;
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interface
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uses
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SysUtils, uItem, uIterator;
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type
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TMenu = class(TObject)
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public
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function CreateIterator: TIterator; virtual; abstract;
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end;
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TDinerMenu = class(TMenu)
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private
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FMenuItem : TMenuItem;
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FMenuItems: TMenuItems;
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FNumberOfItems: Integer;
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public
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constructor Create;
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destructor Destroy; override;
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procedure AddItem(aName, aDescription: String; aVegetarian: Boolean;
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aPrice: Double);
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function CreateIterator: TIterator; override;
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end;
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TWaitress = class(TObject)
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private
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FMenuItem : TMenuItem;
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FDinerMenu: TDinerMenu;
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DinerIterator: TIterator;
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public
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constructor Create(aDinerMenu: TDinerMenu);
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procedure PrintMenu; overload;
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procedure PrintMenu(aIterator: TIterator); overload;
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end;
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implementation
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const
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MAX_TIMES = 6;
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{ TDinerMenu }
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procedure TDinerMenu.AddItem(aName, aDescription: String; aVegetarian: Boolean;
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aPrice: Double);
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begin
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FMenuItem := TMenuItem.Create(aName, aDescription, aVegetarian, aPrice);
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if FNumberOfItems >= MAX_TIMES then
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Writeln('Sorry, menu is full! Can''t add item to menu')
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else
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begin
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FMenuItems[FNumberOfItems] := FMenuItem;
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FNumberOfItems := FNumberOfItems + 1;
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end;
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end;
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constructor TDinerMenu.Create;
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begin
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SetLength(FMenuItems, MAX_TIMES);
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AddItem('Vegetarian BLT',
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'Fakin Bacon with lettuce & tomato on whole Wheat', True, 2.99);
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AddItem('BLT',
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'Bacon with lettuce & tomato on whole Wheat', False, 2.99);
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AddItem('Soup of the day',
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'Soup of the day, with a side of potato salad', False, 3.29);
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AddItem('Hotdog',
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'A hot dog, with saurkraut, relish, onions, topped with cheese',
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False, 3.05);
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AddItem('Steamed Veggies and Brown Rice',
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'Steamed vegetables over brown rice', True, 3.99);
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AddItem('Pasta',
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'Spaghetti with Marinara Sauce, and a slice of sourdough bread', True,
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3.89);
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end;
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destructor TDinerMenu.Destroy;
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begin
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FreeAndNil(FMenuItem);
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inherited;
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end;
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function TDinerMenu.CreateIterator: TIterator;
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begin
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Result := TDinerMenuIterator.Create(FMenuItems);
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end;
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{ TWaitress }
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constructor TWaitress.Create(aDinerMenu: TDinerMenu);
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begin
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FDinerMenu := aDinerMenu;
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end;
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procedure TWaitress.PrintMenu;
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begin
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try
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DinerIterator := FDinerMenu.CreateIterator;
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Writeln('MENU');
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Writeln('----');
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Writeln('BREAKFAST');
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Writeln;
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PrintMenu(DinerIterator);
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finally
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FreeAndNil(DinerIterator);
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end;
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end;
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procedure TWaitress.PrintMenu(aIterator: TIterator);
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begin
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while (aIterator.HasNext) do
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begin
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FMenuItem := (aIterator.Next) as TMenuItem;
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Writeln(FMenuItem.GetName + ',');
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Writeln(FMenuItem.GetPrice, ' -- ');
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Writeln(FMenuItem.GetDescription);
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end;
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end;
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end.

{《HeadFirst设计模式》之迭代器模式 }
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{ 客户端 }
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{ 编译工具：Delphi7.0 }
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{ E-Mail ：guzh-0417@163.com }
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program pMenuTestDrive;
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{$APPTYPE CONSOLE}
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uses
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SysUtils,
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uItem in 'uItem.pas',
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uAggregate in 'uAggregate.pas',
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uIterator in 'uIterator.pas';
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var
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DinerMenu: TDinerMenu;
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Waitress : TWaitress;
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begin
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DinerMenu := TDinerMenu.Create;
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Waitress := TWaitress.Create(DinerMenu);
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Waitress.PrintMenu;
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FreeAndNil(DinerMenu);
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FreeAndNil(Waitress);
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Readln;
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end.

运行结果：

特别感谢：在实现上面示例时，遇到动态数组做参数的问题。感谢盒子论坛里的ZuoBaoQuan兄出手相助！

posted on 2014-11-05 14:34 小光zfg 阅读(291) 评论(0) 收藏举报