[usth/ICT2.7] Engineer software

author: Nguyễn Gia Phong <mcsinyx@disroot.org> 2020-05-24 16:34:31 +0700
committer: Nguyễn Gia Phong <mcsinyx@disroot.org> 2020-05-24 16:34:31 +0700
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tree: 176e1bca6fe644c619d53cf1c24682c244b79cf6 /usth/ICT2.7/P3L3 Design Patterns Subtitles
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diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/1 - Lesson Overview - lang_en_vs4.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/1 - Lesson Overview - lang_en_vs4.srt
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+In the last lesson, we talked about design, and we saw how difficult it can
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+be to come up with a good and effective design for a given software system. To
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+help address these difficulties, we will discuss
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+design patterns, which can support design activities by
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+providing general, reusable solutions to commonly occurring design
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+problems. Similar to architectural styles, design patterns can
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+help developers build better designed systems by reusing design solutions that
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+worked well in the past and by building on those solutions.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/10 - Choosing a Pattern - lang_en_vs5.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/10 - Choosing a Pattern - lang_en_vs5.srt
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+1
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+But with so many patterns, how do we choose a pattern? So
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+this is a possible approach that you can follow. First of all, you
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+want to make sure that you understand your design context. You understand
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+what you're designing and what are the issues involved with this design. What
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+are the problems that you need to solve. At this point, you
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+can examine the patterns catalog, or,if
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+you're already familiar with the catalog, just
+
+8
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+think about the possible patterns that you could use. Once you identify
+
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+the patterns that you can use, you also want to study them and
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+study the related patterns. So normally if you look at any pattern catalog,
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+for each pattern there will also be a list of related patterns. So
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+you can also look at those to see whether maybe some of those
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+might be more applicable. And finally, once you identify the pattern that you
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+think is appropriate, you will apply that pattern. When you do that, just
+
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+be mindful that there are pitfalls in the use of patterns. One obvious
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+one is the fact that you might select the wrong pattern and make
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+your design worse instead of better. The second one is that if you
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+get too excited about patterns, then you
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+might be abusing patterns, so just using too
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+many patterns, and end up with a design
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+that is more complicated rather than less complicated.
+
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+So always be careful, spend the time to figure out which one is the right
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+pattern to apply, and make sure that you
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+don't use patterns that you don't actually need.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/11 - Choosing a Pattern Quiz - lang_en_vs4.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/11 - Choosing a Pattern Quiz - lang_en_vs4.srt
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+1
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+Now that we've discussed how to choose a pattern. Imagine that
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+you have to write a class that can have only one
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+instance. So to satisfy this requirement, I would like for you
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+to pick one of the design patterns that we discussed in
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+this lesson, and write the code here that satisfies that requirement.
+
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+And when you write the code, please make sure that your
+
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+class has only one method, without counting possible constructors, and that
+
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+the class is called Singleton. And write your class right here.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/12 - Choosing a Pattern Quiz Solution - lang_en_vs4.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/12 - Choosing a Pattern Quiz Solution - lang_en_vs4.srt
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+1
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+As we discussed in the class the right thing to
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+do here was to use the factory pattern. So here is
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+3
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+a possible code to solve the problem. Of course that there
+
+4
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+are different possible solutions. So what we did for this code
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+5
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+was to first create a private, static, Singleton object called
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+6
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+instance, which is the one that will keep track of the
+
+7
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+only instance that can be created on the class. Then we
+
+8
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+define the default constructor, the constructor that doesn't take any parameter
+
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+as private. In this way other classes cannot create instances
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+of Singleton without calling our factory method, and finally we
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+create the factory method. And the factory method is very
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+simple. The method will first check whether an instance of
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+the class was already created. If it was created, it
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+would just return that instance. Otherwise, it will create a
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+new instance and assign it to that instance member variable
+
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+and then return the newly created instance. So with this code
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+you're guaranteed that other classes cannot bypass the factory
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+method, because the default constructor is private. And the that
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+the factory method will create one and only one instance
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+of the class, which is exactly what our requirements were.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/13 - Negative Design Patterns - lang_en_vs4.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/13 - Negative Design Patterns - lang_en_vs4.srt
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+To conclude this lesson, I want to discuss the
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+concept of negative design patterns, that is, patterns that should
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+be avoided. Interestingly, negative patterns were also mentioned in
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+Christopher Alexander's book, so in the first formulation of patterns.
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+So negative design pattern are basically guidelines on how
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+not to do things. In consoles with patterns, the guidelines
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+on how to do things. So basically, what the negative
+
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+00:00:21,920 --> 00:00:25,170
+design patterns do is, they enable recurring design defects to
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+be avoided. And as we will see in this class extensively,
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+in mini-course four, negative patterns are
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+also called anti-patterns or bad smells,
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+12
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+or bad code smells. So in mini-course four we will see several
+
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+examples of bad smells and what we can do to eliminate them.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/2 - History of Design Patterns - lang_en_vs6.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/2 - History of Design Patterns - lang_en_vs6.srt
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+1
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+Let's start our decision of design patterns by looking
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+2
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+at the history of patterns. As you know, I like
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+3
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+to give this sort of historical perspective on how and
+
+4
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+when concepts were defined. In this case, we have to
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+5
+00:00:10,600 --> 00:00:14,830
+go back to 1977, when Christopher Alexander, an American professor
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+6
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+of architecture at UC Berkeley, introduces the idea of patterns,
+
+7
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+successful solutions to problems, in his book called a Pattern
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+Language. The book contains about 250 patterns. And the idea
+
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+is that occupants of a building should be able
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+10
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+to design it. And the patterns in the book provide
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+a way to do that. And this idea of design
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+patterns, so, a formal way of documenting successful solutions to
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+problems, inspired several other disciplines. In particular, in 1987,
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+Ward Cunningham and Kent Beck leveraged this idea of Alexander's
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+patterns in the context of an object oriented language.
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+And in this specific the language was Smalltalk.
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+Some of you might know the language. So what Cunningham
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+and Beck did, was to create a 5 pattern
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+language for guiding novice Smalltalk programmers. So they did
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+an experiment and had several developers using their patterns, and
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+the experiment was extremely successful. The users were able to
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+create elegant designs using the provided patterns. And in case
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+you are interested in reading about it, Cunningham and Beck
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+reported the results in the article, Using Pattern Languages for
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+Object Oriented Programs, which was published at the
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+International Conference on Object Oriented Programming, Systems, Languages, and
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+Applications, also called OOPSLA, in 1987. At the
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+same time, Eric Gamma was working on his dissertation,
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+whose topic was the importance of patterns and
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+how to capture them. Between 1987 and 1992, there
+
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+were several workshops related to design patterns. And
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+in 1992, Jim Coplien compiled a catalog of C++
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+items, which are some sort of patterns, and
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+he listed this catalog of patterns in his
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+book, which was titled Advanced C++ Programming Styles
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+and Idioms. Finally, in 1993 and 1994, there were
+
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+00:01:52,952 --> 00:01:56,160
+several additional workshops focused on patterns. And this
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+workshop brought together many patterns folks, including these
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+4 guys, Erich Gamma, Richard Helm, Ralph Johnson,
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+and John Vlissides. These guys are also known as
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+the gang of 4. And the result of this collaboration was the
+
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+famous book Design Patterns: Elements of
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+Reusable Object Oriented Software. So this
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+is basically The Book on design patterns. If you want to buy
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+a book on design pattern, this is the one you should get.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/3 - Patterns Catalogue - lang_en_vs4.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/3 - Patterns Catalogue - lang_en_vs4.srt
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+1
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+This book contains a patterns catalog which is
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+a number of design patterns classified by purpose. And
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+there are five main classes of patterns. There are
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+fundamental patterns which are the basic patterns. There are
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+creational patterns which are the patterns that support object
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+creation. Then there are structural patterns and these are
+
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+patterns that help compose objects, put objects together. The
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+next class of patterns are behavioral patterns and these
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+are patterns that are mostly focused on realizing interactions
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+among different objects. Finally, there are concurrency patterns and these
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+are patterns that support, as the name says, concurrency, so
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+they're more related to concurrency aspects. And for each of
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+these classes there are a number of specific patterns, and
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+here I'm just listing some of them. Clearly we cannot
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+cover in one lesson all of these patterns, but what
+
+16
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+I want to do is to cover at least a few
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+of those to give an idea of what patterns are and
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+how they can be used. In particular, we will see in
+
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+detail the Factory Method Pattern and the Strategy Pattern. And we
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+will also discuss a few more patterns at a higher level.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/4 - Pattern Format - lang_en_vs5.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/4 - Pattern Format - lang_en_vs5.srt
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+1
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+So let's start by seeing how patterns are defined. So
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+2
+00:00:02,711 --> 00:00:05,620
+what is the format of the pattern definitions. If we look
+
+3
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+at the Gang of Four's book we can see that these
+
+4
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+definitions contain a lot of information. In fact, what I'm listing
+
+5
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+here is just a subset of this information. In this lesson,
+
+6
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+what I want to do is to focus on four essential
+
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+elements of a design pattern. It's name, the intent which is
+
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+the goal of the pattern. The pattern's applicability which is the
+
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+list of situations or context in which the
+
+10
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+pattern is applicable. I also want to cover the structure
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+and participants. Which is the static model that describes
+
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+the elements, so normally the classes or the object
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+involved in the pattern. In addition to that
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+the structure also describes
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+15
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+the relationships, responsibilities and collaborations
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+among these classes or objects. Finally what I want
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+to cover is sample code. So examples that illustrate
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+the use of patterns.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/5 - Factory Method Pattern - lang_en_vs5.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/5 - Factory Method Pattern - lang_en_vs5.srt
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+1
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+Let's now look at the first design pattern that we
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+2
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+will discuss, the factory method pattern. And I'm going to start
+
+3
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+by discussing the intent of the pattern and its applicability.
+
+4
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+As far as the intent is concerned, the factory method pattern
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+5
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+allows for creating objects without specifying their class, by invoking
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+what we call a factory method. And what that is, is
+
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+a method whose main goal is to create class instances.
+
+8
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+So when is this pattern useful? So when is it applicable?
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+9
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+For example, it is applicable in cases in which a class
+
+10
+00:00:28,080 --> 00:00:31,890
+cannot anticipate the type of object it must create. That is,
+
+11
+00:00:31,890 --> 00:00:34,800
+the type of an object is not known at compile time,
+
+12
+00:00:34,800 --> 00:00:37,800
+is not known until the code runs. A typical example of
+
+13
+00:00:37,800 --> 00:00:40,500
+this, are frameworks. So if you ever used a framework, you
+
+14
+00:00:40,500 --> 00:00:44,280
+will know that, normally, frameworks only know about interfaces and abstract
+
+15
+00:00:44,280 --> 00:00:47,450
+classes. So the exact type of the objects of these classes
+
+16
+00:00:47,450 --> 00:00:50,840
+is only known at runtime. The second case in which the factory
+
+17
+00:00:50,840 --> 00:00:53,835
+method pattern is applicable, is when a class wants its
+
+18
+00:00:53,835 --> 00:00:57,160
+subclasses to specify the type of objects it creates. And we'll
+
+19
+00:00:57,160 --> 00:00:59,920
+see an example of this in a minute. Finally, factory
+
+20
+00:00:59,920 --> 00:01:03,580
+method patterns are applicable when a class needs control over the
+
+21
+00:01:03,580 --> 00:01:06,760
+creation of its objects. And in this case, one possible
+
+22
+00:01:06,760 --> 00:01:09,380
+example is when there is a limit on the number of
+
+23
+00:01:09,380 --> 00:01:12,930
+objects that can be created. Special example, it's a singleton. If
+
+24
+00:01:12,930 --> 00:01:15,840
+you're familiar with a singleton, a singleton is a class for
+
+25
+00:01:15,840 --> 00:01:18,930
+which only one instance can be created. The factory method pattern
+
+26
+00:01:18,930 --> 00:01:21,760
+is perfect in these cases, because it allows to control how many
+
+27
+00:01:21,760 --> 00:01:24,640
+objects get created. So in this case, it would allow the creation
+
+28
+00:01:24,640 --> 00:01:27,290
+only of a single object. And from the second time that it
+
+29
+00:01:27,290 --> 00:01:30,040
+is invoked, it will just return the object that was previously
+
+30
+00:01:30,040 --> 00:01:33,700
+created. Now let's go ahead and see how this pattern actually works,
+
+31
+00:01:33,700 --> 00:01:37,100
+and let's do that by discussing the structure and the participants for
+
+32
+00:01:37,100 --> 00:01:41,330
+the pattern. The structure that is represented here, using the UML notation,
+
+33
+00:01:41,330 --> 00:01:45,530
+includes three classes, the Creator, the ConcreteCreator,
+
+34
+00:01:45,530 --> 00:01:48,000
+and the Product. The Creator provides the
+
+35
+00:01:48,000 --> 00:01:50,710
+interface for the factory method. So this
+
+36
+00:01:50,710 --> 00:01:53,200
+here, is the interface for the factory method
+
+37
+00:01:53,200 --> 00:01:55,950
+that, when invoked, returns an object of
+
+38
+00:01:55,950 --> 00:01:59,440
+type Product. The ConcreteCreator provides the actual
+
+39
+00:01:59,440 --> 00:02:02,350
+method for creating the Product. So this
+
+40
+00:02:02,350 --> 00:02:06,170
+method is a concrete implementation of this interface.
+
+41
+00:02:06,170 --> 00:02:10,630
+Finally, the Product is the object created by the factory method. So
+
+42
+00:02:10,630 --> 00:02:12,350
+summarizing, we have the interface for
+
+43
+00:02:12,350 --> 00:02:14,300
+the factory method, the actual implementation of
+
+44
+00:02:14,300 --> 00:02:17,540
+the summary method, and the object that is created by the factory method,
+
+45
+00:02:17,540 --> 00:02:21,020
+when it is invoked. So let's look at an example of this pattern.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/6 - Factory Method Pattern Example - lang_en_vs5.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/6 - Factory Method Pattern Example - lang_en_vs5.srt
new file mode 100644
index 0000000..2812c39
--- /dev/null
+++ b/usth/ICT2.7/P3L3 Design Patterns Subtitles/6 - Factory Method Pattern Example - lang_en_vs5.srt
@@ -0,0 +1,127 @@
+1
+00:00:00,220 --> 00:00:03,260
+The example I'm going to use consists of a class called
+
+2
+00:00:03,260 --> 00:00:07,380
+ImageReaderFactory which provides the factory method which is this one;
+
+3
+00:00:07,380 --> 00:00:10,250
+createImageReader. As you can see the method takes an InputStream
+
+4
+00:00:10,250 --> 00:00:13,570
+as input and returns an object of type ImageReader, and it's
+
+5
+00:00:13,570 --> 00:00:15,645
+static so that we can invoke it even if we
+
+6
+00:00:15,645 --> 00:00:18,390
+don't have an instance of the ImageReaderFactory. So what does the
+
+7
+00:00:18,390 --> 00:00:22,275
+method do? Well the method first invokes, getImageType, passing the
+
+8
+00:00:22,275 --> 00:00:25,780
+InputStream as a parameter and this method figures out the type
+
+9
+00:00:25,780 --> 00:00:28,820
+of the image that is stored in this Inputstream and it's
+
+10
+00:00:28,820 --> 00:00:32,740
+an integer. Then, based on the value of this integer, the
+
+11
+00:00:32,740 --> 00:00:35,352
+method does one of several things. If the image type is
+
+12
+00:00:35,352 --> 00:00:38,970
+a GIF, it will invoke the constructor for GifReader passing the
+
+13
+00:00:38,970 --> 00:00:41,610
+stream as a parameter. And what will happen is that the
+
+14
+00:00:41,610 --> 00:00:44,450
+GIF reader will read a GIF from the stream, create a
+
+15
+00:00:44,450 --> 00:00:47,887
+corresponding object and return it. So in this case, the ImageReader
+
+16
+00:00:47,887 --> 00:00:51,460
+object return will be the object representing a GIF as appropriate.
+
+17
+00:00:51,460 --> 00:00:54,610
+Similarly, if the image type is JPEG, then the method will
+
+18
+00:00:54,610 --> 00:00:58,579
+invoke the constructor for JPEG Reader and in this case, this constructor
+
+19
+00:00:58,579 --> 00:01:01,981
+will read from the stream a JPEG, create a corresponding object
+
+20
+00:01:01,981 --> 00:01:05,640
+and return it. And so on for different types of images. So
+
+21
+00:01:05,640 --> 00:01:07,880
+why is this a situation in which it is appropriate to
+
+22
+00:01:07,880 --> 00:01:11,100
+use the factory method pattern? One, because it corresponds exactly to the
+
+23
+00:01:11,100 --> 00:01:14,250
+cases that we saw before, of applicability. This is a case
+
+24
+00:01:14,250 --> 00:01:16,560
+in which we don't know the type of the object that we
+
+25
+00:01:16,560 --> 00:01:20,080
+need to create until we run the code, because it depends
+
+26
+00:01:20,080 --> 00:01:22,530
+on the value of the InputStream. It depends on the content
+
+27
+00:01:22,530 --> 00:01:25,590
+of the InputStream. So, until we read the InputStream, we cannot
+
+28
+00:01:25,590 --> 00:01:28,380
+figure out whether we need to create a GIF, a JPEG or
+
+29
+00:01:28,380 --> 00:01:30,780
+some other type of image. So in this case, we want to
+
+30
+00:01:30,780 --> 00:01:33,630
+do, we want to simply delegate to this classes the creation of
+
+31
+00:01:33,630 --> 00:01:35,610
+the object, once we know what type of object needs to
+
+32
+00:01:35,610 --> 00:01:38,790
+be created. So perfect example of application of a factory method pattern.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/7 - Strategy Pattern - lang_en_vs5.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/7 - Strategy Pattern - lang_en_vs5.srt
new file mode 100644
index 0000000..288b8d6
--- /dev/null
+++ b/usth/ICT2.7/P3L3 Design Patterns Subtitles/7 - Strategy Pattern - lang_en_vs5.srt
@@ -0,0 +1,143 @@
+1
+00:00:00,230 --> 00:00:02,110
+The second pattern I want to discuss is the
+
+2
+00:00:02,110 --> 00:00:05,050
+strategy pattern, which provides a way to configure a
+
+3
+00:00:05,050 --> 00:00:07,900
+class with one of many behaviors. What does that
+
+4
+00:00:07,900 --> 00:00:11,040
+mean? Well, more precisely, this pattern allows for defining
+
+5
+00:00:11,040 --> 00:00:15,330
+a family of algorithms, encapsulating them into separate classes,
+
+6
+00:00:15,330 --> 00:00:17,900
+so each algorithm in one class, and making these
+
+7
+00:00:17,900 --> 00:00:21,490
+classes interchangeable, but providing a common interface for all
+
+8
+00:00:21,490 --> 00:00:25,350
+the encapsulated algorithms. So in essence, the intent of
+
+9
+00:00:25,350 --> 00:00:29,250
+a strategy pattern is to allow for switching between
+
+10
+00:00:29,250 --> 00:00:33,490
+different algorithms for accomplishing a given task. For example, imagine
+
+11
+00:00:33,490 --> 00:00:36,610
+having different sorting algorithms with different space or time
+
+12
+00:00:36,610 --> 00:00:38,800
+tradeoffs. You might want to be able to have them
+
+13
+00:00:38,800 --> 00:00:42,670
+all available and use different ones in different situations.
+
+14
+00:00:42,670 --> 00:00:44,820
+And this pattern is applicable not only when we have
+
+15
+00:00:44,820 --> 00:00:47,260
+different variants of an algorithm, but also when we
+
+16
+00:00:47,260 --> 00:00:51,690
+have many related classes that differ only in their behavior.
+
+17
+00:00:51,690 --> 00:00:53,640
+So let's get more concrete and see how this is
+
+18
+00:00:53,640 --> 00:00:55,960
+done. And I'm going to do it as before, by
+
+19
+00:00:55,960 --> 00:00:59,700
+discussing the structure and the participants for this strategy pattern.
+
+20
+00:00:59,700 --> 00:01:02,540
+In this case, we have 3 types of participants for this
+
+21
+00:01:02,540 --> 00:01:07,210
+pattern, the context, the algorithm, and the concrete strategies. There
+
+22
+00:01:07,210 --> 00:01:09,580
+can be as many as the number of behaviors that
+
+23
+00:01:09,580 --> 00:01:12,300
+I need to implement. So, let's see what those are.
+
+24
+00:01:12,300 --> 00:01:16,690
+The context is the interface to the outside world. It maintains
+
+25
+00:01:16,690 --> 00:01:19,180
+a reference to the current algorithm and allows for
+
+26
+00:01:19,180 --> 00:01:22,860
+updating this reference at run time. So, basically the outside
+
+27
+00:01:22,860 --> 00:01:26,370
+world will invoke the functionality provided by the different algorithms,
+
+28
+00:01:26,370 --> 00:01:29,170
+by using this interface. And depending on which algorithm is
+
+29
+00:01:29,170 --> 00:01:31,640
+currently selected, that's the one that will be executed when
+
+30
+00:01:31,640 --> 00:01:35,920
+the functionality is involved. The algorithm, also called the strategy,
+
+31
+00:01:35,920 --> 00:01:37,970
+so that's where the pattern gets its name, Is the
+
+32
+00:01:37,970 --> 00:01:42,130
+common interface for the different algorithims. So all the algorithms
+
+33
+00:01:42,130 --> 00:01:46,690
+implement this interface. Finally, the concrete strategies are the
+
+34
+00:01:46,690 --> 00:01:49,920
+actual implementations of the algorithms. So if I have 10
+
+35
+00:01:49,920 --> 00:01:53,030
+different variants of my algorithm, I will implement 10 different
+
+36
+00:01:53,030 --> 00:01:56,550
+concrete strategies. They will all be implementations of this interface.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/8 - Strategy Pattern Example & Demo - lang_en_vs5.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/8 - Strategy Pattern Example & Demo - lang_en_vs5.srt
new file mode 100644
index 0000000..6d298d0
--- /dev/null
+++ b/usth/ICT2.7/P3L3 Design Patterns Subtitles/8 - Strategy Pattern Example & Demo - lang_en_vs5.srt
@@ -0,0 +1,511 @@
+1
+00:00:00,130 --> 00:00:03,320
+Now let's see how this whole thing works in practice by
+
+2
+00:00:03,320 --> 00:00:06,800
+using an example. We're going to consider a program that takes as
+
+3
+00:00:06,800 --> 00:00:10,450
+input a text file and produce it as output, a filtered
+
+4
+00:00:10,450 --> 00:00:14,170
+file. So basically it outputs a subset of the content of
+
+5
+00:00:14,170 --> 00:00:16,928
+this text file based on some filter. And we're going to have
+
+6
+00:00:16,928 --> 00:00:19,440
+four different types of filters. So the first one is
+
+7
+00:00:19,440 --> 00:00:21,680
+not filtering which means that the whole content of the text
+
+8
+00:00:21,680 --> 00:00:25,320
+file will be produced on the output. The second filter will output
+
+9
+00:00:25,320 --> 00:00:27,990
+only words that starts with t. So you'll take the text file
+
+10
+00:00:27,990 --> 00:00:30,540
+and simply ignore all of the words that do not start with
+
+11
+00:00:30,540 --> 00:00:33,130
+t. So in the output we'll have only those words that starts
+
+12
+00:00:33,130 --> 00:00:36,030
+with letter t. The third filter will produce in the output only
+
+13
+00:00:36,030 --> 00:00:39,180
+words that are longer than five characters. So all the other words
+
+14
+00:00:39,180 --> 00:00:43,740
+will be simply disregarded. And finally, the four filter will produce as
+
+15
+00:00:43,740 --> 00:00:47,630
+output only words in the text file that are palindromes, and in
+
+16
+00:00:47,630 --> 00:00:50,590
+case you don't know what a palindrome is, a palindrome is a word
+
+17
+00:00:50,590 --> 00:00:52,700
+that is the same whether you read it from left
+
+18
+00:00:52,700 --> 00:00:55,800
+to right or from right to left. For example, the
+
+19
+00:00:55,800 --> 00:00:58,480
+word kayak, you can read it in this direction, or
+
+20
+00:00:58,480 --> 00:01:00,740
+in this direction, and it's exactly the same word. So
+
+21
+00:01:00,740 --> 00:01:03,560
+let's see how this program could be implemented using a
+
+22
+00:01:03,560 --> 00:01:05,980
+strategy pattern. And let's do it for real as a
+
+23
+00:01:05,980 --> 00:01:10,100
+demo. What we're looking at here is the editor page
+
+24
+00:01:10,100 --> 00:01:15,520
+for Eclipse, open with the strategy pattern implementation for our example.
+
+25
+00:01:15,520 --> 00:01:17,130
+So what I'm going to do is that, I'm going to look at a
+
+26
+00:01:17,130 --> 00:01:20,310
+different part of implementation. And you will see that, you know, despite
+
+27
+00:01:20,310 --> 00:01:23,420
+the fact that it's slightly longer, it's really fairly simple, it's kind
+
+28
+00:01:23,420 --> 00:01:26,230
+of a straightforward implementation of what we just saw. As I just
+
+29
+00:01:26,230 --> 00:01:29,820
+said, what we are doing is basically building the strategy patterns that
+
+30
+00:01:29,820 --> 00:01:34,330
+allows for changing the strategies with which we're filtering an input file.
+
+31
+00:01:34,330 --> 00:01:37,380
+And we have different strategies, we'll look at those in detail, and
+
+32
+00:01:37,380 --> 00:01:41,050
+we said that the three participants for this pattern are the context,
+
+33
+00:01:41,050 --> 00:01:43,650
+the algorithm, which is the general interface and then the concrete
+
+34
+00:01:43,650 --> 00:01:47,270
+strategies, which are the concrete implementations of this algorithm. So let's
+
+35
+00:01:47,270 --> 00:01:49,790
+start by looking at the context. Which is this class here.
+
+36
+00:01:49,790 --> 00:01:52,960
+And as you can see it contains a reference at the current
+
+37
+00:01:52,960 --> 00:01:56,240
+strategy. We call this the check strategy, which is basically our
+
+38
+00:01:56,240 --> 00:01:59,910
+filter, and when the context is created by default it sets a
+
+39
+00:01:59,910 --> 00:02:02,890
+strategy to the old strategy. The old strategy is the one
+
+40
+00:02:02,890 --> 00:02:06,380
+that accepts all the input, so basically it doesn't filter out anything.
+
+41
+00:02:06,380 --> 00:02:08,320
+And we said that the context is the interface to the
+
+42
+00:02:08,320 --> 00:02:10,889
+outside world, right? So it has to provide the outside world
+
+43
+00:02:10,889 --> 00:02:14,140
+with a way of selecting the strategy, the specific algorithm to
+
+44
+00:02:14,140 --> 00:02:16,850
+be used, and it does that in this case by providing
+
+45
+00:02:16,850 --> 00:02:21,360
+this change strategy method. This method takes a strategy as input,
+
+46
+00:02:21,360 --> 00:02:24,930
+and simply replaces the current strategy with the one specified as
+
+47
+00:02:24,930 --> 00:02:28,035
+a parameter. And at this point, the context also will perform
+
+48
+00:02:28,035 --> 00:02:31,830
+the filtering. The filtering is pretty straightforward, so what it does is
+
+49
+00:02:31,830 --> 00:02:34,620
+that it opens a file that is passed as a parameter
+
+50
+00:02:34,620 --> 00:02:37,450
+so that this the file, the input file to be filtered. And
+
+51
+00:02:37,450 --> 00:02:40,560
+then it reads the file line by line and then splits
+
+52
+00:02:40,560 --> 00:02:43,620
+the lines into its composing words and then for each word in
+
+53
+00:02:43,620 --> 00:02:46,480
+each line, what it will do, it will basically invoke the
+
+54
+00:02:46,480 --> 00:02:50,270
+check method in the current strategy, which is basically the filtering method
+
+55
+00:02:50,270 --> 00:02:53,580
+and if the check method returns true, which basically means that
+
+56
+00:02:53,580 --> 00:02:57,150
+the word should be printed, it prints the word. Otherwise, it'll just
+
+57
+00:02:57,150 --> 00:03:00,480
+skip it. So basically the filter will return false for all the
+
+58
+00:03:00,480 --> 00:03:03,470
+words that have to be filtered out. Okay? This is the basic
+
+59
+00:03:03,470 --> 00:03:06,770
+way in which context works. Let's see how this is used in
+
+60
+00:03:06,770 --> 00:03:10,660
+our main method. The main method simply creates the context, reads the input file
+
+61
+00:03:10,660 --> 00:03:12,910
+from the arguments, and then what he does is simply as a
+
+62
+00:03:12,910 --> 00:03:16,720
+demonstration, it will perform the filtering using all the different filters. So
+
+63
+00:03:16,720 --> 00:03:19,310
+starting from the default one, which is the one that basically doesn't
+
+64
+00:03:19,310 --> 00:03:22,150
+do any filtering that reports all words, then it will switch to the
+
+65
+00:03:22,150 --> 00:03:25,400
+algorithm, that only considers the words that start with t, and
+
+66
+00:03:25,400 --> 00:03:28,880
+it will do that by invoking a change strategy and passing this
+
+67
+00:03:28,880 --> 00:03:30,890
+strategy as the argument, and then
+
+68
+00:03:30,890 --> 00:03:32,760
+performing the actual filtering through context.
+
+69
+00:03:32,760 --> 00:03:35,040
+And it will do exactly the same for the strategy that only
+
+70
+00:03:35,040 --> 00:03:37,540
+prints words that are longer than five and the one that
+
+71
+00:03:37,540 --> 00:03:40,460
+only prints words that are palindromes. So now let's look at the
+
+72
+00:03:40,460 --> 00:03:44,090
+actual algorithm. This is the interface, the algorithm interface. And you can
+
+73
+00:03:44,090 --> 00:03:47,080
+see that the only thing that the interface provides is this method,
+
+74
+00:03:47,080 --> 00:03:49,760
+which is the check method, that takes a string as input and will
+
+75
+00:03:49,760 --> 00:03:52,470
+return a boolean. So, basically, it's the boolean that we were seeing before.
+
+76
+00:03:52,470 --> 00:03:55,010
+The one that is true for the words that have to be printed
+
+77
+00:03:55,010 --> 00:03:57,490
+and false for the ones that have to be filtered out. Now, we have
+
+78
+00:03:57,490 --> 00:04:01,250
+all the different implementations of the algorithm, the simplest one is the all
+
+79
+00:04:01,250 --> 00:04:05,110
+algorithm, the simple return is always true, so all the words will be printed.
+
+80
+00:04:05,110 --> 00:04:08,740
+The second one starts with t, and again, without looking at the details
+
+81
+00:04:08,740 --> 00:04:10,660
+of implementations that don't really matter, what
+
+82
+00:04:10,660 --> 00:04:12,390
+it does is basically check that
+
+83
+00:04:12,390 --> 00:04:15,111
+the first character is t, and returns true in that case and
+
+84
+00:04:15,111 --> 00:04:17,720
+false otherwise. Similarly, for the LongerThan5
+
+85
+00:04:17,720 --> 00:04:19,380
+algorithm, also in this case, this
+
+86
+00:04:19,380 --> 00:04:23,000
+will implement the check strategy interface, and the check will be performed
+
+87
+00:04:23,000 --> 00:04:25,980
+by checking that the word is longer than five characters and returning
+
+88
+00:04:25,980 --> 00:04:29,440
+true in that case and false otherwise. And finally the Palindrome check
+
+89
+00:04:29,440 --> 00:04:32,240
+is a little more complicated, but basically it just checks whether the
+
+90
+00:04:32,240 --> 00:04:35,190
+word is a Palindrome and returns true in that case. Okay, so
+
+91
+00:04:35,190 --> 00:04:37,950
+as I said, it doesn't really matter too much what is the specific
+
+92
+00:04:37,950 --> 00:04:40,630
+implementations of these matters. What matters is that we have
+
+93
+00:04:40,630 --> 00:04:44,150
+a general interface for the algorithm and then any different concrete
+
+94
+00:04:44,150 --> 00:04:48,130
+implementations of the algorithm that implement different strategies. So again,
+
+95
+00:04:48,130 --> 00:04:50,730
+this allows you to change the behavior of your class without
+
+96
+00:04:50,730 --> 00:04:53,420
+changing class. So we have this context class that does
+
+97
+00:04:53,420 --> 00:04:57,015
+different things when the filter method in invoked, depending on what
+
+98
+00:04:57,015 --> 00:04:59,930
+is the current strategy. So the behavior of the class can
+
+99
+00:04:59,930 --> 00:05:03,310
+change dynamically, and it changes dynamically every time that we change
+
+100
+00:05:03,310 --> 00:05:06,300
+the strategy. At this point, the way this whole thing works should
+
+101
+00:05:06,300 --> 00:05:08,430
+be clear, so what we're going to do is that we're going to go to
+
+102
+00:05:08,430 --> 00:05:12,010
+our console, and we're actually going to run the strategy pattern and see
+
+103
+00:05:12,010 --> 00:05:15,710
+what happens. So here I have a file, it's called foo.txt. And if
+
+104
+00:05:15,710 --> 00:05:18,290
+we look at the content of foo, you can see that it
+
+105
+00:05:18,290 --> 00:05:21,190
+says that this is just a test to assess how well this program
+
+106
+00:05:21,190 --> 00:05:24,430
+performs when used on files of text. And since it checks for
+
+107
+00:05:24,430 --> 00:05:28,560
+palindromes, we will also insert one such word, level. Level is a palindrome,
+
+108
+00:05:28,560 --> 00:05:31,042
+because you can read it from both sides. Okay, so let's
+
+109
+00:05:31,042 --> 00:05:33,657
+see what happens when we run our code. So we're going to
+
+110
+00:05:33,657 --> 00:05:36,900
+run java pattern.strategy.StrategyPattern which is
+
+111
+00:05:36,900 --> 00:05:38,550
+our class, and we going to fetch
+
+112
+00:05:38,550 --> 00:05:41,460
+foo.txt as an input, and let's go back to the beginning
+
+113
+00:05:41,460 --> 00:05:43,980
+of the output to see what happened exactly. You can see
+
+114
+00:05:43,980 --> 00:05:48,040
+here that for the default strategy, which was the old strategy,
+
+115
+00:05:48,040 --> 00:05:50,810
+the whole file is printed, so every word is printed. This
+
+116
+00:05:50,810 --> 00:05:53,485
+is just a test to assess and so on and so forth,
+
+117
+00:05:53,485 --> 00:05:57,290
+as expected. For the filter that only prints words that
+
+118
+00:05:57,290 --> 00:06:00,230
+start with t, only words that start with t are printed,
+
+119
+00:06:00,230 --> 00:06:04,180
+again, as expected. Similarly, for the filter that only prints words
+
+120
+00:06:04,180 --> 00:06:06,970
+that are longer than 5, and finally for the one that prints
+
+121
+00:06:06,970 --> 00:06:09,540
+palindromes. And here you can see that we actually have two
+
+122
+00:06:09,540 --> 00:06:12,410
+because the way in which this is implemented we'll also consider
+
+123
+00:06:12,410 --> 00:06:15,300
+single letter words as palindromes because you can read them from
+
+124
+00:06:15,300 --> 00:06:18,450
+both sides. But you definitely will also have level in the output.
+
+125
+00:06:18,450 --> 00:06:21,040
+And in case you want to play with this code yourself, I
+
+126
+00:06:21,040 --> 00:06:24,600
+have made this code and also the implementation for examples of other
+
+127
+00:06:24,600 --> 00:06:28,440
+design partners available as a compressed archive. And the archive is accessible
+
+128
+00:06:28,440 --> 00:06:31,120
+through a URL that is provided in the notes for the cost.
diff --git a/usth/ICT2.7/P3L3 Design Patterns Subtitles/9 - Other Common Patterns - lang_en_vs5.srt b/usth/ICT2.7/P3L3 Design Patterns Subtitles/9 - Other Common Patterns - lang_en_vs5.srt
new file mode 100644
index 0000000..756f38f
--- /dev/null
+++ b/usth/ICT2.7/P3L3 Design Patterns Subtitles/9 - Other Common Patterns - lang_en_vs5.srt
@@ -0,0 +1,295 @@
+1
+00:00:00,060 --> 00:00:03,460
+Before concluding this lesson, let's look at a few more patterns. And
+
+2
+00:00:03,460 --> 00:00:05,880
+although it will take too long to cover them in detail, I
+
+3
+00:00:05,880 --> 00:00:08,986
+would like to at least mention and quickly discuss a few more
+
+4
+00:00:08,986 --> 00:00:12,080
+of these more commonly-used patterns. In fact, some of the patterns that
+
+5
+00:00:12,080 --> 00:00:15,400
+I will discuss, you might have used yourself. Maybe without knowing their
+
+6
+00:00:15,400 --> 00:00:18,300
+name or the fact that they were design patterns. So let's start
+
+7
+00:00:18,300 --> 00:00:21,660
+with a Visitor pattern, which is a way of separating an algorithm
+
+8
+00:00:21,660 --> 00:00:25,150
+from an object structure on which it operates. And a practical result
+
+9
+00:00:25,150 --> 00:00:28,010
+of this separation is the ability to add the new operation
+
+10
+00:00:28,010 --> 00:00:31,680
+to exist in object structures, without modifying the structures. So, basically
+
+11
+00:00:31,680 --> 00:00:34,540
+what this pattern does, is to allow for defining and easily
+
+12
+00:00:34,540 --> 00:00:37,870
+modifying set of operations to perform on the objects of the collection.
+
+13
+00:00:37,870 --> 00:00:40,570
+And the typical usage of this is, for example, when you're
+
+14
+00:00:40,570 --> 00:00:43,140
+visiting a graph, or a set of objects, and you want
+
+15
+00:00:43,140 --> 00:00:46,090
+to perform some operations on these objects. By using a visitor
+
+16
+00:00:46,090 --> 00:00:48,410
+pattern, you can decouple the operation
+
+17
+00:00:48,410 --> 00:00:50,830
+from the objects. Although not straightforward,
+
+18
+00:00:50,830 --> 00:00:53,360
+this pattern is very, very useful. So, I really encourage you
+
+19
+00:00:53,360 --> 00:00:56,060
+to look at it in more detail and get familiar with it.
+
+20
+00:00:56,060 --> 00:00:59,040
+The second pattern I want to mention is the decorator pattern.
+
+21
+00:00:59,040 --> 00:01:02,820
+The decorator pattern is basically a wrapper that adds functionality to a
+
+22
+00:01:02,820 --> 00:01:05,030
+class. So the way in which it works, is that you
+
+23
+00:01:05,030 --> 00:01:08,230
+will take a class, you will build a class that basically wraps
+
+24
+00:01:08,230 --> 00:01:12,250
+this class. So it reproduces the functionality of the original class, but
+
+25
+00:01:12,250 --> 00:01:15,900
+it also adds some functionality. And for all the functionality that was
+
+26
+00:01:15,900 --> 00:01:18,750
+already in the original class, it will simply invoke this
+
+27
+00:01:18,750 --> 00:01:21,080
+functionality and for the new one, you will implement it
+
+28
+00:01:21,080 --> 00:01:24,510
+using the services of the class. And a nice property
+
+29
+00:01:24,510 --> 00:01:26,760
+of the decorator pattern is that it's stackable. So you can
+
+30
+00:01:26,760 --> 00:01:30,210
+add decorators on decorators on decorators, and further increase the
+
+31
+00:01:30,210 --> 00:01:34,052
+functionality provided by your class. The iterator is another very
+
+32
+00:01:34,052 --> 00:01:37,810
+commonly-used pattern. And, you probably use this one yourself because,
+
+33
+00:01:37,810 --> 00:01:41,090
+it's also part of many standard libraries. What the iterator allows
+
+34
+00:01:41,090 --> 00:01:44,220
+you to do, is basically to access elements of a collection
+
+35
+00:01:44,220 --> 00:01:47,490
+without knowing the underlying representation. So the iterator will allow you
+
+36
+00:01:47,490 --> 00:01:50,630
+to just go through a set of objects without worrying about
+
+37
+00:01:50,630 --> 00:01:53,200
+how the objects are stored. So you basically just ask the
+
+38
+00:01:53,200 --> 00:01:55,810
+iterator to give you the first object, the next object and
+
+39
+00:01:55,810 --> 00:02:00,130
+so on. Another very commonly-used pattern is the observer pattern. And
+
+40
+00:02:00,130 --> 00:02:02,650
+this pattern is very useful when you have an object of
+
+41
+00:02:02,650 --> 00:02:06,190
+interest and a set of other objects that are interested in
+
+42
+00:02:06,190 --> 00:02:09,240
+the changes that might occur in this first object. So
+
+43
+00:02:09,240 --> 00:02:12,690
+what the observer pattern allows you to do is to register
+
+44
+00:02:12,690 --> 00:02:15,460
+these objects, so that they let the system know that
+
+45
+00:02:15,460 --> 00:02:18,690
+they're interested in changes in this first object. And then, every
+
+46
+00:02:18,690 --> 00:02:20,840
+time that there is a change, these other objects will
+
+47
+00:02:20,840 --> 00:02:23,030
+be automatically notified. So basically,
+
+48
+00:02:23,030 --> 00:02:25,290
+the observer pattern allows for notifying
+
+49
+00:02:25,290 --> 00:02:29,310
+dependents when an object of interest changes. If you want
+
+50
+00:02:29,310 --> 00:02:32,020
+an example of this, just think about the file system and
+
+51
+00:02:32,020 --> 00:02:35,870
+imagine having a folder. All the views of this folder will
+
+52
+00:02:35,870 --> 00:02:37,970
+want to be notified every time that there's a change in
+
+53
+00:02:37,970 --> 00:02:40,720
+the folder because they need to refresh. So instead of continuously
+
+54
+00:02:40,720 --> 00:02:44,390
+checking the state of the folder, they will just register and basically
+
+55
+00:02:44,390 --> 00:02:47,430
+say, hey, we're interested in knowing when something changes in this
+
+56
+00:02:47,430 --> 00:02:50,320
+folder. And when something changes in the folder, they will be automatically
+
+57
+00:02:50,320 --> 00:02:53,300
+notified. So it will be some sort of a push notification
+
+58
+00:02:53,300 --> 00:02:56,590
+instead of a pull notification, if you are familiar with that terminology.
+
+59
+00:02:56,590 --> 00:03:00,020
+Finally the proxy pattern is a pattern in which a surrogate
+
+60
+00:03:00,020 --> 00:03:04,370
+controls access to an object. In other words, we have our object,
+
+61
+00:03:04,370 --> 00:03:07,220
+and we have our proxy here. So all the requests to the
+
+62
+00:03:07,220 --> 00:03:09,950
+object will go through the proxy that will then forward them. And
+
+63
+00:03:09,950 --> 00:03:12,020
+all the responses from the object will also go through the
+
+64
+00:03:12,020 --> 00:03:15,580
+proxy. They will then forward them to the original requester. So what
+
+65
+00:03:15,580 --> 00:03:18,710
+the proxy allows you to do is to control how this object,
+
+66
+00:03:18,710 --> 00:03:22,180
+that is behind the proxy, is actually accessed, for example, by filtering
+
+67
+00:03:22,180 --> 00:03:24,500
+some calls. So in a sense, the proxy allows use
+
+68
+00:03:24,500 --> 00:03:27,470
+for masking some of the functionality of the object that
+
+69
+00:03:27,470 --> 00:03:31,070
+is behind the proxy. And there's many, many, many more
+
+70
+00:03:31,070 --> 00:03:34,424
+useful patterns. That can help you when designing and implementing
+
+71
+00:03:34,424 --> 00:03:37,220
+the system. So once more, I really encourage you to
+
+72
+00:03:37,220 --> 00:03:38,740
+have a look at the book, to look at the
+
+73
+00:03:38,740 --> 00:03:41,570
+resources online, and to really get more familiar with these
+
+74
+00:03:41,570 --> 00:03:43,890
+patterns, and to try to use them in your everyday work.
author	Nguyễn Gia Phong <mcsinyx@disroot.org>	2020-05-24 16:34:31 +0700
committer	Nguyễn Gia Phong <mcsinyx@disroot.org>	2020-05-24 16:34:31 +0700
commit	b2d80610db6beda38573890ed169815e495bc663 (patch)
tree	176e1bca6fe644c619d53cf1c24682c244b79cf6 /usth/ICT2.7/P3L3 Design Patterns Subtitles
parent	49376ab97c7427f1c1eca64072d1a934c2e52f50 (diff)
download	cp-b2d80610db6beda38573890ed169815e495bc663.tar.gz