1. Summary prepared by Kirk Scott
Chapter 4 Façade
Summary prepared by Kirk Scott

2. Emmer From Wikipedia, the free encyclopedia
Emmer wheat (Triticum dicoccum), also known as farro especially in Italy, or hulled wheat,[1] is a type of awned wheat. It was one of the first crops domesticated in the Near East. It was widely cultivated in the ancient world, but is now a relict crop in mountainous regions of Europe and Asia.

4. Spelt From Wikipedia, the free encyclopedia
This article is about the wheat species.
For the alternative version of the word "spelled", see Spelling.Spelt, also known as dinkel wheat,[2] or hulled wheat,[2] is a hexaploid species of wheat. Spelt was an important staple in parts of Europe from the Bronze Age to medieval times; it now survives as a relict crop in Central Europe and northern Spain and has found a new market as a health food. Spelt is sometimes considered a subspecies of the closely related species common wheat (T. aestivum), in which case its botanical name is considered to be Triticum aestivum subsp. spelta.

6. Einkorn wheat From Wikipedia, the free encyclopedia   (Redirected from Einkorn)
Einkorn wheat (from German Einkorn, literally "single grain") can refer either to the wild species of wheat, Triticum boeoticum , or to the domesticated form, Triticum monococcum. The wild and domesticated forms are either considered separate species, as here, or as subspecies of T. monococcum. Einkorn is a diploid species of hulled wheat, with tough glumes ('husks') that tightly enclose the grains. The cultivated form is similar to the wild, except that the ear stays intact when ripe and the seeds are larger.

7. Einkorn wheat was one of the earliest cultivated forms of wheat, alongside emmer wheat (T. dicoccum). Grains of wild einkorn have been found in Epi-Paleolithic sites of the Fertile Crescent. It was first domesticated approximately 7500 BC (7050 BC ≈ 9000 BP), in the Pre-Pottery Neolithic A (PPNA) or B (PPNB) periods.[1] Evidence from DNA finger-printing suggests einkorn was domesticated near Karaca Dağ in southeast Turkey, an area in which a number of PPNB farming villages have been found.[2] Its cultivation decreased in the Bronze Age, and today it is a relict crop that is rarely planted, though it has found a new market as a health food. It remains as a local crop, often for bulgur (cracked wheat) or as animal feed, in mountainous areas of France, Morocco, the former Yugoslavia, Turkey and other countries. It often survives on poor soils where other species of wheat fail.[3]

9. Design Patterns in Java Chapter 4 Façade
Summary prepared by Kirk Scott

10. Façade
The book starts with a review of some of the benefits of object-oriented code development
The idea is that families/hierarchies of classes are developed which are known as toolkits
Then application programs can be written which make use of the functionality implemented in the toolkits

11. In the broadest sense, you might think of the Java API as a toolkit
This would be an example of a toolkit that has too much in it to fully understand
How do you know what features to use or where to start when trying to use it to implement an application?

12. The façade design pattern is an approach to managing the complexity of a toolkit
The book describes a façade as a “small amount” of code which provides a typical, no-frills usage of the classes in a class library
It expands this description by saying that a façade is a class with a level of functionality between a toolkit and an application

13. This class offers simplified usage of the classes in a package or subsystem (the toolkit)
It can do this by providing an interface with fewer methods
It can also do this by providing an interface containing methods with fewer parameters

14. Book Definition of the Design Pattern
The intent of the Façade pattern is to provide an interface that makes a subsystem easy to use

15. The book will take two approaches to illustrating what a façade is
The first approach is to point out a class in the Java API which it says meets the definition of a façade
The second approach will be to give a concrete example of a design, including code, and refactor it to reflect the façade pattern

16. The refactoring involves adding new classes to the design and dividing methods among them.
A basic design question is always, what are the classes and what functionality do they contain?
You may get this right in an initial design or you may have to rethink it on a redesign

17. The façade pattern can be used as a model for abstracting out certain functionalities into one class, the façade
The remaining functionalities are then reorganized in a set of classes that is more logical or convenient

18. Facades and Utilities
If a class fits the intent of the Façade design pattern and consists entirely of static methods, then it is called a utility
A utility can be a useful construct
Incidentally, with a utility, you can’t override static methods in subclasses

19. Facades don’t have to consist entirely of static methods
If you develop a façade, in theory it would be possible to give it subclasses
You could override methods as necessary
There is no particular reason to pursue this line of thinking in order to understand the design pattern

20. Facades and Demos
A demo is an example that shows how to use a class or subsystem
Demos provide much of the same information or value to the programmer as a façade, but they are not exactly the same thing
The book lists several ways in which they differ

21. “A demo is usually a stand-alone application; a façade is usually not.
A demo usually includes sample data; a façade does not.
A façade is usually configurable; a demo is not
A façade is intended for reuse; a demo is not
A façade is intended for use in production; a demo is not”

22. An Example of a Façade in the Java API
The book gives the JOptionPane class from the Java API as an example of a façade
If you look in the API documentation, this class has dozens of methods of its own and it inherits literally hundreds of others
It is in the javax.swing package, and it can be used in the writing of graphical user interface code

23. It is impossible to say how many discrete elements of the swing package the JOptionPane class is based on, or provides a way of using
The book provides one simple example of its use
It gives an application that pops up a confirm dialog box

24. This is done with a static call to the JOptionPane class
There is no reason to look at the complete code where the call occurs
The one line of code in question looks like this
option = JOptionPane.showConfirmDialog(…);
Its output is shown on the next overhead

26. In the code for Echo1.java there was a line of code like this
The use of the JOptionPane should not be foreign to you, because it was used in unit 17 of CSCE 222
In the code for Echo1.java there was a line of code like this
inputString = JOptionPane.showInputDialog(…);
Its output is shown on the next overhead

28. The book makes the following statements:
“The JOptionPane class is one of the few examples of a Façade in the Java class libraries.
It is production worthy, configurable, and designed for reuse.
Above all else, the JOptionPane class fulfills the intent of the Façade pattern by providing a simple interface that makes it easy to use the JDialog class.

29. JOptionPane has dozens of static methods that effectively make it a utility as well as a façade.
Strictly speaking, though, it does not meet the UML definition of a utility, which requires it to possess solely static methods.”
[End of solution 4.2]

30. You might argue that a façade simplifies a “subsystem” and that the solitary JDialog class does not qualify as a subsystem.
But it is exactly the richness of this class’s features that make a façade valuable.

31. Challenge 4.3
“Few facades appear in the Java class libraries. Why is that?”

32. Solution 4.3:
“Here are a few reasonable but opposing views regarding the paucity of facades in the Java class libraries.
[given on the following overheads]

33. [1] As a Java developer, you are well advised to develop a thorough knowledge of the tools in the library.
Facades necessarily limit the way you might apply any system.
They would be a distracting and potentially misleading element of the class libraries in which they might appear.

34. [2] A façade lies somewhere between the richness of a toolkit and the specificity of a particular application.
To create a façade requires some notion of the type of applications it will support.
This predictability is impossible given the huge and diverse audience of the Java class libraries.

35. [3] The scarcity of facades in the class libraries is a weakness.
Adding more facades would be a big help.”

36. Parametric Equations: A Detour
The book’s next example is based on an application that presents graphical representations of parabolic flight paths of rockets
You will see that this is closely related to some of the things that happened both visually and with the use of functions that cropped up in the MVC example with graphs of thrust and burn rate

37. This example and the MVC example raise the issue of how best to do graphical things based on mathematical formulas in Java
These questions have nothing to do with the façade design pattern, so they will not be covered in depth
However, they have to be covered somewhat in order to follow the example

38. Every example more complicated than rock-bottom will have a context
Graphing in an application can be a significant implementation concern

39. The correct use of parametric equations can make the graphing of mathematical equations much neater and clearer
The book devotes a subsection to the use of parametric equations
For the purposes of understanding the example application, the topic of parametric equations will be covered now

40. Parametric Equations: An Initial Example
In Java, graphical objects are generally determined by (x, y, w, h)—in other words, their location is specified by an (x, y) pair
One example of a case where parametric equations would be useful is when you are interested in plotting a mathematical relationship which isn’t a mathematical function

41. In other words, for a given value of x, the relationships has more than one value of y
A circle in Cartesian coordinates is an example
The equation for the circle centered at the origin with radius 1 is x2 + y2 = 1.
If you solve for y, you get y = ±√(1 – x2), which is not a function
For each x value there are 2 y values

42. However, you could switch your representation scheme to polar coordinates
For a circle with its center at the origin, r = a constant
This is a very simple function
You can then translate from polar to Cartesian coordinates

43. Solving for x and y gives:
For a circle of radius r, for any angle θ (consider the range 0 to 2π), these relationships hold:
sin θ = y / r
cos θ = x / r
Solving for x and y gives:
y = r sin θ
x = r cos θ

44. Polar coordinates arise as a natural alternative to Cartesian coordinates
The last two equations given above illustrate parameterization
Instead of one equation, you have two equations jointly expressing the values of x and y in terms of r and θ

45. x and y are expressed in terms of a constant r, and a variable, or parameter, θ
These two equations for x and y are functions of θ
There is no confusion about ± values

46. Parametric Equations: Matching Equations to the Requirements of Java Graphing
Converting a given equation to a parametric form can also be useful even if the equation is already a function
Consider some of the challenges of representing a mathematical function using the simple graphical capabilities of Java

47. A. You have to match up the actual width of the display panel in Java with the range of values x takes on in the function of interest
B. You have to do the same for y.
C. You also have to deal with the fact that in Cartesian coordinates, the positive y axis points up, while in Java, the positive y axis points down

48. Parameterizing an equation can give expressions for x and y that take into account the inversion of y and the width and height of the display panel
The code can be written so that the width and height of the display area, w and h, are variables or input parameters to display methods
The graphing code automatically factors changes in w or h, namely, the dimensions of the display panel, into the output values of x and y

49. Parametric Equations: Fireworks Flight Paths
The book’s example code involves displaying the trajectory of a shell
This is a projectile that is shot without any propellant of its own (it’s not a rocket)
If air resistance and wind are ignored, and if the shell doesn’t explode in mid-air and it returns to earth, its flight path is a simple parabola
Sample output from their example application is shown on the following overhead

51. In general, a parabola has a quadratic equation of the form y = x2
A parabola with this simple equation would have its vertex at the origin and it would open upward
This is a function, but it is desirable to parameterize it so that we can display it nicely

52. In addition to fitting the display panel, the parameterization should deal with the orientation and location of the parabola in the panel
The book empirically derives some parametric equations for this scenario

53. How to Parameterize
The first task in parameterizing is to decide on a parameter
In many physical cases it is customary to use the variable t, denoting time
In practice, t might range from some given starting time to some given ending time
In this example, it may be thought of as representing time—but not clock time

54. It is useful to normalize t, having it start at 0 and end at 1
Then any value of t between 0 and 1 represents the proportion of time that has passed between the beginning and the end of some physical process
It is not really necessary to think of this as time at all
It can be regarded as a useful mathematical convenience and nothing more

55. Parameterizing x Consider the x axis for a function
It will correspond to the x axis in a Java
It runs positive from left to right in both Cartesian coordinates and Java display
Parameterizing x involves making its range of values correspond to the amount of time that has passed

56. Practically speaking, what you want to accomplish from parameterization is this:
t takes on values from 0 to 1
x depends on t
As t goes from 0 to 1, x takes on the values from 0 to w, the width of the panel in which the graph is to be displayed

57. Notice how, by default, the range of x values has been dealt with in the statement of the problem.
The range of x starts at 0, not at some negative value to the left of the origin, as would be the case for a centered graph of y = x2

58. The book gives this parametric equation for x, which satisfies this requirement:
x = w * t
As the value of t goes from 0 to 1, the value of x goes from 0 to w.

59. Parameterizing y Taking care of y involves a few more steps
Recall the general form y = x2
If you simply graphed that equation in Cartesian coordinates, the vertex would be at the origin and the parabola would open upward
However, the parabola for a flight path has its vertex at the top center of the display panel, and the parabola opens downward

60. Parameterizing y involves making its range of values correspond to the amount of time that has passed
Practically speaking, what you want to accomplish from parameterization is this:
t takes on values from 0 to 1
y depends on t

61. These 3 things have to be achieved:
1. The vertex of the parabola is centered in the panel
2. The parabola opens downward (y is inverted)
3. As t goes from 0 to 1, y takes on values between 0 and h, the height of the panel in which the graph is to be displayed

62. 1. Centering the Vertex
The x coordinate of the vertex should be at the midpoint of the panel the graph is displayed in
The x coordinate of the vertex would correspond to half of w, and in terms of t, it would correspond to half of t

63. The goal is to have the min value for y, 0, occur at the center of w
This parametric equation for y has the vertex in the middle:
y = (t – .5)(t – .5)
When t = .5, y = 0
When t = 0 or 1, y = (.5)(.5) = .25

64. 2. Inverting y
The y coordinate of the vertex should be at the top of the panel the graph is displayed in and the parabola should open downward
This “inversion” in y turns out not be an issue at all
Because positive y points downward in Java graphics, no adjustment has to be made to the parametric equation

65. 3. y Takes on Values Between 0 and h
The next step is to normalize the maximum value attained by y to 1
To do this, you introduce a constant to offset the product’s giving a maximum value of .25
In other words, you introduce a factor of 4 into the parametric equation:
y = 4(t – .5)(t – .5)

66. The last step is to include h as a variable so that the maximum value of y is h:
y = 4h(t – .5)(t – .5)

67. The End Result of Parameterization
Together, then, these are the parametric equations:
x = wt
y = 4h(t – .5)(t – .5)
The parameter t defines the quadratic relationship between x and y

68. The shape of the parabola as graphed will depend on the constant 4 and the variables w and h
In other words, the shape as shown on the display will not be “purely” y = x2
The graph will be stretched or squeezed so that it fits perfectly into the bounds defined by w and h

69. Applying Facade
As usual, the book gives an initial example and then refactors to façade
This presentation will simply go directly to the façade example
Shown on the next overhead is the output of the example

71. The façade based design will have these features:
1. A Function class with a method f() that accepts a double (the value of time) and returns a double (the function’s value)
Two subclasses of the Function class which contain the code for parametric equations of x and y respectively

72. 2. A PlotPanel class that shows the flight of a shell
The PlotPanel class will do plotting by receiving objects of the Function class, which generate the needed x and y values
3. There will be a UI class, which is the façade in the design
It will contain a method named createTitledPanel(), which is the visible output

73. An incomplete UML diagram which outlines the design listed above is shown on the following overhead
It shows a design for the ShowFlight application divided into a set of classes so that each has one job

75. Challenge 4.4
“Complete the diagram in Figure 4.5 to show the code for ShowFlight refactored into three types:
a Function class, a PlotPanel class that plots two parametric functions, and a UI façade class.
In your redesign, make the ShowFlight2 class create a Function for y values, and have a main() method that launches the application.”

76. Solution 4.4

77. Disappointment Note that the given solution is incomplete
In particular the facade, the UI class, is floating in space
This is a disappointment
The goal is to understand the façade pattern
The UI class is the façade
But what is its relationship to the other classes in the example application?

78. Redemption
The UI class contains the createTitledPanel() method in the application
Where is this called from?
It is called from main()
In other words, in the UML diagram one missing link is between the ShowFlight2 class and the UI class

79. The ShowFlight2 class makes use of the PlotPanel class to generate the contents of the graphical elements
The ShowFlight2 class makes use of the façade class in generating the standardized graphical elements of the application that will be displayed

80. In other words, in complete code, in a complete UML diagram, you would see this:
Main() calls the UI to make the titled panel
It also creates an instance of PlotPanel
The titled panel wraps the PlotPanel

81. So what is the UI a façade to?
That is the magic question, and the diagram simply doesn’t show it
This is the answer:
The UI class, the façade, stands in front of graphical elements existing in the Java API

82. This is a good example, because it shows how your code might make use of a façade into the system supplied classes
Your own code may be simple enough that you don’t need a façade into it
On the other hand, it’s funny that at the end the authors leave out the final, explanatory pieces

83. Another Missing Element in the Diagram
There is another missing link in the diagram
The Function class is floating in space
The PlotPanel class paintComponent() method relies on the Function class to contain the logic for generating the points of a parabola
In other words, the other missing link in the UML diagram is between the PlotPanel Class and the Function class

84. Considering the UML for the Pattern Again
Here the diagram for the façade pattern is considered in the context of the preceding pattern, the mediator
Literally, the mediator is the class “in between”
The façade is the class “in front of”
Practically, though, the façade is also “in between” whatever it’s in front of and whatever makes use of what it’s in front of

85. On the overhead following the next one, two UML diagrams are shown
The first is my simplified mediator diagram, repeated for the sake of comparison
The second is an attempt to abstract out and simplify the façade pattern
The dashed arrows in the façade diagram are meant to indicate “makes use of”

86. The basic idea is this:
For the mediator, either the references both go into the mediator, or both go out, (or maybe there are references both ways)
For the façade, the references form a directed path
The client uses the façade, which in turn uses the toolkit
The end result is that the client uses the toolkit

88. The End