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：
1
2{《HeadFirst设计模式》之迭代器模式 }
3{ 容器中的元素类 }
4{ 编译工具：Delphi7.0 }
5{ E-Mail ：[email protected] }
6
7unit uItem;
8
9interface
10
11type
12 TMenuItem = class(TObject)
13 private
14 FName: String;
15 FDescription: String;
16 FVegetarian : Boolean;
17 FPrice: Double;
18 public
19 constructor Create(aName, aDescription: String;
20 aVegetarian : Boolean;
21 aPrice: Double);
22 function GetName: String;
23 function GetDescription: String;
24 function GetPrice: Double;
25 function IsVegetarian: Boolean;
26 end;
27
28implementation
29
30{ TMenuItem }
31
32constructor TMenuItem.Create(aName, aDescription: String;
33 aVegetarian: Boolean;
34 aPrice: Double);
35begin
36 FName := aName;
37 FDescription := aDescription;
38 FVegetarian := aVegetarian;
39 FPrice := aPrice;
40end;
41
42function TMenuItem.GetDescription: String;
43begin
44 Result := FDescription;
45end;
46
47function TMenuItem.GetName: String;
48begin
49 Result := FName;
50end;
51
52function TMenuItem.GetPrice: Double;
53begin
54 Result := FPrice;
55end;
56
57function TMenuItem.IsVegetarian: Boolean;
58begin
59 Result := FVegetarian;
60end;
61
62end.
1
2{《HeadFirst设计模式》之迭代器模式 }
3{ 迭代器：封装对容器的遍历 }
4{ 编译工具：Delphi7.0 }
5{ E-Mail ：[email protected] }
6
7unit uIterator;
8
9interface
10
11uses
12 uItem;
13
14type
15 TMenuItems = array of TMenuItem;
16
17 TIterator = class(TObject)
18 public
19 function HasNext: Boolean; virtual; abstract;
20 function Next : TObject; virtual; abstract;
21 end;
22
23 TDinerMenuIterator = class(TIterator)
24 private
25 FMenuItem : TMenuItem;
26 FMenuItems: TMenuItems;
27 FPosition : Integer;
28 public
29 constructor Create(MenuItems: TMenuItems);
30 function HasNext: Boolean; override;
31 function Next : TObject; override;
32 end;
33
34implementation
35
36{ TDinerMenuIterator }
37
38constructor TDinerMenuIterator.Create(MenuItems: TMenuItems);
39begin
40 FMenuItems := MenuItems;
41end;
42
43function TDinerMenuIterator.HasNext: Boolean;
44begin
45 if (FPosition < Length(FMenuItems)) and (FMenuItems[FPosition] <> nil) then
46 Result := True
47 else
48 Result := False;
49end;
50
51function TDinerMenuIterator.Next: TObject;
52begin
53 FMenuItem := FMenuItems[FPosition];
54 FPosition := FPosition + 1 ;
55 Result := FMenuItem;
56end;
57
58end.
1
2{《HeadFirst设计模式》之迭代器模式 }
3{ 容器类及其用户： Waitress }
4{ 编译工具：Delphi7.0 }
5{ E-Mail ：[email protected] }
6
7unit uAggregate;
8
9interface
10
11uses
12 SysUtils, uItem, uIterator;
13
14type
15 TMenu = class(TObject)
16 public
17 function CreateIterator: TIterator; virtual; abstract;
18 end;
19
20 TDinerMenu = class(TMenu)
21 private
22 FMenuItem : TMenuItem;
23 FMenuItems: TMenuItems;
24 FNumberOfItems: Integer;
25 public
26 constructor Create;
27 destructor Destroy; override;
28 procedure AddItem(aName, aDescription: String; aVegetarian: Boolean;
29 aPrice: Double);
30 function CreateIterator: TIterator; override;
31 end;
32
33 TWaitress = class(TObject)
34 private
35 FMenuItem : TMenuItem;
36 FDinerMenu: TDinerMenu;
37 DinerIterator: TIterator;
38 public
39 constructor Create(aDinerMenu: TDinerMenu);
40 procedure PrintMenu; overload;
41 procedure PrintMenu(aIterator: TIterator); overload;
42 end;
43
44implementation
45
46const
47 MAX_TIMES = 6;
48
49{ TDinerMenu }
50
51procedure TDinerMenu.AddItem(aName, aDescription: String; aVegetarian: Boolean;
52 aPrice: Double);
53begin
54 FMenuItem := TMenuItem.Create(aName, aDescription, aVegetarian, aPrice);
55 if FNumberOfItems >= MAX_TIMES then
56 Writeln(‘Sorry, menu is full! Can‘‘t add item to menu‘)
57 else
58 begin
59 FMenuItems[FNumberOfItems] := FMenuItem;
60 FNumberOfItems := FNumberOfItems + 1;
61 end;
62end;
63
64constructor TDinerMenu.Create;
65begin
66 SetLength(FMenuItems, MAX_TIMES);
67
68 AddItem(‘Vegetarian BLT‘,
69 ‘Fakin Bacon with lettuce & tomato on whole Wheat‘, True, 2.99);
70 AddItem(‘BLT‘,
71 ‘Bacon with lettuce & tomato on whole Wheat‘, False, 2.99);
72 AddItem(‘Soup of the day‘,
73 ‘Soup of the day, with a side of potato salad‘, False, 3.29);
74 AddItem(‘Hotdog‘,
75 ‘A hot dog, with saurkraut, relish, onions, topped with cheese‘,
76 False, 3.05);
77 AddItem(‘Steamed Veggies and Brown Rice‘,
78 ‘Steamed vegetables over brown rice‘, True, 3.99);
79 AddItem(‘Pasta‘,
80 ‘Spaghetti with Marinara Sauce, and a slice of sourdough bread‘, True,
81 3.89);
82end;
83
84destructor TDinerMenu.Destroy;
85begin
86 FreeAndNil(FMenuItem);
87 inherited;
88end;
89
90function TDinerMenu.CreateIterator: TIterator;
91begin
92 Result := TDinerMenuIterator.Create(FMenuItems);
93end;
94
95{ TWaitress }
96
97constructor TWaitress.Create(aDinerMenu: TDinerMenu);
98begin
99 FDinerMenu := aDinerMenu;
100end;
101
102procedure TWaitress.PrintMenu;
103begin
104 try
105 DinerIterator := FDinerMenu.CreateIterator;
106 Writeln(‘MENU‘);
107 Writeln(‘----‘);
108 Writeln(‘BREAKFAST‘);
109 Writeln;
110 PrintMenu(DinerIterator);
111 finally
112 FreeAndNil(DinerIterator);
113 end;
114end;
115
116procedure TWaitress.PrintMenu(aIterator: TIterator);
117begin
118 while (aIterator.HasNext) do
119 begin
120 FMenuItem := (aIterator.Next) as TMenuItem;
121 Writeln(FMenuItem.GetName + ‘,‘);
122 Writeln(FMenuItem.GetPrice, ‘ -- ‘);
123 Writeln(FMenuItem.GetDescription);
124 end;
125end;
126
127end.
1
2{《HeadFirst设计模式》之迭代器模式 }
3{ 客户端 }
4{ 编译工具：Delphi7.0 }
5{ E-Mail ：[email protected] }
6
7program pMenuTestDrive;
8
9{$APPTYPE CONSOLE}
10
11uses
12 SysUtils,
13 uItem in ‘uItem.pas‘,
14 uAggregate in ‘uAggregate.pas‘,
15 uIterator in ‘uIterator.pas‘;
16
17var
18 DinerMenu: TDinerMenu;
19 Waitress : TWaitress;
20
21begin
22 DinerMenu := TDinerMenu.Create;
23 Waitress := TWaitress.Create(DinerMenu);
24 Waitress.PrintMenu;
25
26 FreeAndNil(DinerMenu);
27 FreeAndNil(Waitress);
28 Readln;
29end.
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！