Errata

Line -15
Inserted after the words web site, the phrase http://patterns.cs.up.ac.za. There is also an official
O'Reilly website at

Inserted after the last line:
My sincere thanks to all the readers who have send in comments and suggested corrections. I
particularly wish to thank Philip Fitzimmons, Dominik Gruntz and Brian Holland for their careful
reading of the text. Jim Whitehead, Nigel Horspool and Alastair van Leeuwen continually make me
defend my corner in the nicest possible way, leading to a better book all round.
Judith Bishop
July 2008

Line -15
Inserted after the words web site, the phrase http://patterns.cs.up.ac.za. There is also an official
O’Reilly website at

Inserted after the last line:
My sincere thanks to all the readers who have send in comments and suggested corrections. I
particularly wish to thank Philip Fitzimmons, Dominik Gruntz and Brian Holland for their careful
reading of the text. Jim Whitehead, Nigel Horspool and Alastair van Leeuwen continually make me
defend my corner in the nicest possible way, leading to a better book all round.
Judith Bishop
July 2008

Line 12
Replaced "inherits" with "implements"

Line 12
Replaced inherits from by implements

Line 13
Removed this line entirely (IComponent Any Photo). It is a duplicate of the first line in the table.

Line 13
Removed this line entirely (IComponent Any Photo). It is a duplicate of the first line in the table.

Line -11
Replaced Tag with TaggedPhoto keeping the courier font

Line -8
Replaced Tag with TaggedPhoto keeping the courier font

Line -7
Replaced Tag with TaggedPhoto keeping the courier font

Line –11
Replaced Tag with TaggedPhoto keeping the courier font

Line –8
Replaced Tag with TaggedPhoto keeping the courier font

Line –7
Replaced Tag with TaggedPhoto keeping the courier font

Line 1
Replaced Tags with TaggedPhoto class keeping the courier font for the first word only

Line 1
Replaced Tag with TaggedPhoto keeping the courier font

Line 1
Replaced Tags with TaggedPhoto class keeping the courier font for the first word only

Line 1
Replaced Tag with TaggedPhoto keeping the courier font

Line 8
Inserted the word static in courier font before the word List and moved everything so that static
lines up under static just above it in line 7

Line 8
Inserted the word static in courier font before the word List and moved everything so that static
lines up under static just above it in line 7

Lines -15 to -13
Replaced Exercise 1 entirely by the following:
1 Referring to Example 2-1, write a new DecoratorC and experiment with new calls to the Display
method from the Main method in the Client to produce different effects.

Lines –15 to –13
Replaced Exercise 1 entirely by the following:
1 Referring to Example 2-1, write a new DecoratorC and experiment with new calls to the Display
method from the Main method in the Client to produce different effects.

Line -6
Added closing parenthesis after proxy

Line –6
Added closing parenthesis after proxy

Line -2
Removed the word ProtectionProxy and move the line back so that subject lines up above Console on the
last line.

Line –2
Removed the word ProtectionProxy and move the line back so that subject lines up above Console on the
last line.

Line 16
Replaced RealSpaceBook by SpaceBook in the same font

Line 17
Replaced RealSpaceBook by SpaceBook in the same font

Line 21
Replaced IsUnique by IsUsed in the same font

Line 16
Replaced RealSpaceBook by SpaceBook in the same font

Line 17
Replaced RealSpaceBook by SpaceBook in the same font

Line 21
Replaced IsUnique by IsUsed in the same font

Line 7
Replaced Unique by IsUsed in the same font

Line -2
Lined Today I worked 18 hours up under Hello World

Line 7
Replaced Unique by IsUsed in the same font

Line 17
Deleted the first the

Line –2
Lined Today I worked 18 hours up under Hello World

Line 19
Replaced SpaceBook with MySpaceBook in the same font

Line 20
Replaced SpaceBook with MySpaceBook in the same font

Line 19
Replaced SpaceBook by MySpaceBook in the same font

Line 20
Replaced SpaceBook by MySpaceBook in the same font

Line 9
Replaced IsUnique by IsUsed in the same font

Line -2
Replaced Unique with IsUsed in the same font

Line 9
Replaced IsUnique by IsUsed in the same font

Line –2
Replaced Unique by IsUsed in the same font

Line 20
Lined Today I worked 18 hours up under Hello World

Line 20
Lined Today I worked 18 hours up under Hello World

Captions
The Captions on these two figures are interchanged.

Under the larger screen shot that comes first we want:
Figure 2-6 Bridge pattern illustration (a) --environment Path variable set to Version 3.5

Under the smaller screen shot we want
Figure 2-7. Bridge pattern illustration (b) -- five versions of the .NET Framework installed

Captions
The Captions on these two figures are interchanged.

Under the larger screen shot that comes first we want:
Figure 2-6 Bridge pattern illustration (a) – environment Path variable set to Version 3.5

Under the smaller screen shot we want
Figure 2-7. Bridge pattern illustration (b) – five versions of the .NET Framework installed

Fig 3-2
Delete the arrowed line between Component and Composite.
Create a line from IComponent down to Composite with an open arrow on the Composite end.

Lines 6 and 7
Replaced all the code on these two pages by this code:

1 using System;
2 using System.Collections.Generic;
3 using System.Text; // for StringBuilder
4
5 // Composite Pattern Theory Judith Bishop Dec 2006, Aug 2007
6 // Arranges structures hierarchies so that single components and
7 // composite groups of components can be treated in the same way.
8 // Revised July 2008
9
10 namespace CompositePattern {
11
12 // The Interface
13 public interface IComponent <T> {
14 void Add(IComponent <T> c);
15 IComponent <T> Remove(T s);
16 string Display(int depth);
17 IComponent <T> Find(T s);
18 T Name {get; set;}
19 }
20
21 // The Component
22 public class Component <T> : IComponent <T> {
23 public T Name {get; set;}
24
25 public Component (T name) {
26 Name = name;
27 }
28
29 public void Add(IComponent <T> c) {
30 Console.WriteLine("Cannot add to an item");
31 }
32
33 public IComponent <T> Remove(T s) {
34 Console.WriteLine("Cannot remove directly");
35 return this;
36 }
37
38 public string Display(int depth) {
39 return new String('-', depth) + Name+"
";
40 }
41
42 public IComponent <T> Find (T s) {
43 if (s.Equals(Name))
44 return this;
45 else
46 return null;
47 }
48 }
49
50 // The Composite
51 public class Composite <T> : IComponent <T> {
52 List <IComponent <T>> list;
53
54 public T Name {get; set;}
55
56 public Composite (T name) {
57 Name = name;
58 list = new List <IComponent <T>> ();
59 }
60
61 public void Add(IComponent <T> c) {
62 list.Add(c);
63 }
64
65 // Finds the item from a particular point in the structure
66 // and returns the composite from which it was removed
67 // If not found, return the point as given
68 public IComponent <T> Remove(T s) {
69 IComponent <T> p = this.Find(s);
70 if (this!=null) {
71 (this as Composite<T>).list.Remove(p);
72 }
73 return this;
74 }
75
76 // Recursively looks for an item
77 // Returns its reference or else null
78 public IComponent <T> Find (T s) {
79 if (Name.Equals(s)) return this;
80 IComponent <T> found=null;
81 foreach (IComponent <T> c in list) {
82 found = c.Find(s);
83 if (found!=null)
84 break;
85 }
86 return found;
87 }
88
89 // Displays items in a format indicating their level
90 // in the composite structure
91 public string Display(int depth) {
92 StringBuilder s =
93 new StringBuilder(new String('-', depth));
94 s.Append("Set "+ Name + " length :" + list.Count + "
");
95 foreach (IComponent <T> component in list)
96 s.Append(component.Display(depth + 2));
97 return s.ToString();
98 }
99 }
100 }

Lines 6 and 7
Replaced all the code on these two pages by this code:

1 using System;
2 using System.Collections.Generic;
3 using System.Text; // for StringBuilder
4
5 // Composite Pattern Theory Judith Bishop Dec 2006, Aug 2007
6 // Arranges structures hierarchies so that single components and
7 // composite groups of components can be treated in the same way.
8 // Revised July 2008
9
10 namespace CompositePattern {
11
12 // The Interface
13 public interface IComponent <T> {
14 void Add(IComponent <T> c);
15 IComponent <T> Remove(T s);
16 string Display(int depth);
17 IComponent <T> Find(T s);
18 T Name {get; set;}
19 }
20
21 // The Component
22 public class Component <T> : IComponent <T> {
23 public T Name {get; set;}
24
25 public Component (T name) {
26 Name = name;
27 }
28
29 public void Add(IComponent <T> c) {
30 Console.WriteLine("Cannot add to an item");
31 }
32
33 public IComponent <T> Remove(T s) {
34 Console.WriteLine("Cannot remove directly");
35 return this;
36 }
37
38 public string Display(int depth) {
39 return new String('-', depth) + Name+"
";
40 }
41
42 public IComponent <T> Find (T s) {
43 if (s.Equals(Name))
44 return this;
45 else
46 return null;
47 }
48 }
49
50 // The Composite
51 public class Composite <T> : IComponent <T> {
52 List <IComponent <T>> list;
53
54 public T Name {get; set;}
55
56 public Composite (T name) {
57 Name = name;
58 list = new List <IComponent <T>> ();
59 }
60
61 public void Add(IComponent <T> c) {
62 list.Add(c);
63 }
64
65 // Finds the item from a particular point in the structure
66 // and returns the composite from which it was removed
67 // If not found, return the point as given
68 public IComponent <T> Remove(T s) {
69 IComponent <T> p = this.Find(s);
70 if (this!=null) {
71 (this as Composite<T>).list.Remove(p);
72 }
73 return this;
74 }
75
76 // Recursively looks for an item
77 // Returns its reference or else null
78 public IComponent <T> Find (T s) {
79 if (Name.Equals(s)) return this;
80 IComponent <T> found=null;
81 foreach (IComponent <T> c in list) {
82 found = c.Find(s);
83 if (found!=null)
84 break;
85 }
86 return found;
87 }
88
89 // Displays items in a format indicating their level
90 // in the composite structure
91 public string Display(int depth) {
92 StringBuilder s =
93 new StringBuilder(new String('-', depth));
94 s.Append("Set "+ Name + " length :" + list.Count + "
");
95 foreach (IComponent <T> component in list)
96 s.Append(component.Display(depth + 2));
97 return s.ToString();
98 }
99 }
100 }

Line 2
Replaced "37-42" by "42-47"

Line 5
Replaced 33-35 by 91-98

Line 9
Replaced 46 by 51

Line 14
Replaced 47 by 52

Line 19
Replaced 65-74 by 68-74

Line 21
Replaced 69 by 71

Line 22
Replaced the word holder with this in the same font

Line 23
Replaced
The holder variable is of type ...
with
The this object could be of type ...

Line 26
Replaced 82 and 94 with 81 and 95

Line -6
Example Photo Library is now an "A" heading


Line 2
Replaced 37–42 by 42–47

Line 5
Replaced 33-35 by 91–98

Line 9
Replaced 46 by 51

Line 14
Replaced 47 by 52

Line 19
Replaced 65–74 by 68–74

Line 21
Replaced 69 by 71

Line 22
Replaced the word holder by this in the same font

Line 23
Replaced
The holder variable is of type …
by
The this object could be of type …

Line 26
Replaced 82 and 94 by 81 and 95

Line -6
Example Photo Library is now an "A" heading


Line -9
Removed space in front of Set

Line –9
Removed space in front of Set

Line 6
Removed space in front of Set

Line 6
Removed space in front of Set

Line -17
Inserted a colon after <T> i.e. <T>:

Line –17
Inserted a colon after <T> i.e. <T>:

Line 15
Changed from "first of our four features" to "first of our five features"

Line 15
Changed from "first of our four features" to "first of our five features"

Line 19
Added t he instruction (See over) after "indexers".

Lines 26-29
Deleted these five lines, i.e. lines 6-9 of the code fragment

Line -8
Replaced 13-14 by 9-10

Line -6
Replaced 13 by 9 and 14 by 10

Line -5
Replaced 10-16 with 6-12

Line -4
Replaced 10 with 6

Line -3
Replaced 12-14 by 8-10

Line 19
Added after indexers. The instruction (See over.)

Lines 26-29
Deleted these five lines, i.e. lines 6-9 of the code fragment

Line –8
Replaced 13–14 by 9–10

Line –6
Replaced 13 by 9 and 14 by 10

Line –5
Replaced 10–16 by 6–12

Line –4
Replaced 10 by 6

Line –3
Replaced 12–14 by 8–10

Line -8
Replaced collection with array

Line –8
Replaced collection by array

Lines 11-22
Replaced entirely by this code:

// Flyweight
public struct Flyweight : IFlyweight {
// Intrinsic state
Image pThumbnail;
public void Load (string filename) {
pThumbnail = new Bitmap("images/"+filename).
GetThumbnailImage(100, 100, null, new IntPtr());
}

public void Display(PaintEventArgs e, int row, int col) {
// Calculating extrinsic state
e.Graphics.DrawImage(pThumbnail,col*100+10, row*130+40,
pThumbnail.Width,pThumbnail.Height);
}
}

Lines 11–22
Replaced entirely by this code:

// Flyweight
public struct Flyweight : IFlyweight {
// Intrinsic state
Image pThumbnail;
public void Load (string filename) {
pThumbnail = new Bitmap("images/"+filename).
GetThumbnailImage(100, 100, null, new IntPtr());
}

public void Display(PaintEventArgs e, int row, int col) {
// Calculating extrinsic state
e.Graphics.DrawImage(pThumbnail,col*100+10, row*130+40,
pThumbnail.Width,pThumbnail.Height);
}
}

Lines –14 to –16
Deleted these three lines and the blank line below.

Line -5
Replaced DifferentRequest with SpecificRequest in the same font

Line –5
Replaced DifferentRequest by SpecificRequest in the same font

Line 8
Replaced interfaces with from both classes

Line 8
Replaced interfaces by from both classes

Line 17
Inserted after the word respectively:
There is also another set of generic delegates introduced with the name Action that represent methods
that do not return a value.

Line 17
Inserted after the word respectively:
There is also another set of generic delegates introduced with the name Action that represent methods
that do not return a value.

Lines -14 -12 -8 -5 -1
Replaced all occurrences of Façade in courier font by Facade in courier font (no cidilla). Removing
the cidilla only applies to the courier Façade, not when the word is used in plain text.

Lines -14 -12 -8 -5 -1
Replaced all occurrences of Façade in courier font by Facade in courier font (no cidilla). Removing
the cidilla only applies to the courier Façade, not when the word is used in plain text.

Lines -12 -6 -2
Replaced all occurrences of Façade in courier font by Facade in courier font (no cidilla).

Lines -12 -6 -2
Replaced all occurrences of Façade in courier font by Facade in courier font (no cidilla).

Lines 6 7 9 10
Replaced all occurrences of Façade in courier font by Facade in courier font (no cidilla).

Lines 6 7 9 10
Replaced all occurrences of Façade in courier font by Facade in courier font (no cidilla).

Fig 5-3
Inside the box called Creator, the last word should be IProduct not Product

Line 14
Replaced Shoekeeper with Shopkeeper

Line 14
Replaced Shoekeeper by Shopkeeper

Line 14
Removed the detail (3)

Line 14
Removed the detail (3)

Line -6
Replaced Instance by UniqueInstance in the same font

Line -6
Replaced Instance by UniqueInstance in the same font

Line -8
Replaced 25-27 by 26-28

Line -8
Replaced 25-27 by 26-28

Line 21
Replaced 49 by 59

Line 21
Replaced 49 by 59

Fig 7-2
The box on the left should be called Context not Client

Fig 8-2
The large box in the centre called IHandler:
Change its name to IHandler (not italic).
The word Handler should be IHandler in plain (not italic) arial font
There should be a line coming out of the top of this box, along, down and back into the box on its
right side, with an open diamond at this end.

Line 1
Replaced Mediator constructor with Mediator's sign on method with mediator in courier font.

Line 1
Replaced Mediator constructor by Mediator’s sign on method with mediator in courier font.

Fig 10-3
Remove the line between Client and Visitor1 boxes
Add a dotted line out the top of the Client box into the left side IVisitor box at the top. There
should be an open arrow on the Visitor side of the line.

Fig 10-5
Remove the line between the Terminal and Nonterminal boxes.
Replace the name of the Term box by ITerm
Add a solid line out of the right side of ITerm coming down to the top of Nonterminal with an open
diamond on this end.

Line -4
Replaced GetMemento by Restore

Line -8
Replaced SetMemento by Save

Line -4
Replaced GetMemento by Restore