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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 deleted file mode 100644 index 152b961..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/1 - Lesson Overview - lang_en_vs4.srt +++ /dev/null @@ -1,31 +0,0 @@ -1 -00:00:00,230 --> 00:00:04,560 -In the last lesson, we talked about design, and we saw how difficult it can - -2 -00:00:04,560 --> 00:00:10,010 -be to come up with a good and effective design for a given software system. To - -3 -00:00:10,010 --> 00:00:12,620 -help address these difficulties, we will discuss - -4 -00:00:12,620 --> 00:00:16,560 -design patterns, which can support design activities by - -5 -00:00:16,560 --> 00:00:20,710 -providing general, reusable solutions to commonly occurring design - -6 -00:00:20,710 --> 00:00:25,410 -problems. Similar to architectural styles, design patterns can - -7 -00:00:25,410 --> 00:00:30,400 -help developers build better designed systems by reusing design solutions that - -8 -00:00:30,400 --> 00:00:33,730 -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 deleted file mode 100644 index f273441..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/10 - Choosing a Pattern - lang_en_vs5.srt +++ /dev/null @@ -1,95 +0,0 @@ -1 -00:00:00,150 --> 00:00:03,200 -But with so many patterns, how do we choose a pattern? So - -2 -00:00:03,200 --> 00:00:05,970 -this is a possible approach that you can follow. First of all, you - -3 -00:00:05,970 --> 00:00:09,140 -want to make sure that you understand your design context. You understand - -4 -00:00:09,140 --> 00:00:12,800 -what you're designing and what are the issues involved with this design. What - -5 -00:00:12,800 --> 00:00:15,200 -are the problems that you need to solve. At this point, you - -6 -00:00:15,200 --> 00:00:17,160 -can examine the patterns catalog, or,if - -7 -00:00:17,160 --> 00:00:18,750 -you're already familiar with the catalog, just - -8 -00:00:18,750 --> 00:00:22,430 -think about the possible patterns that you could use. Once you identify - -9 -00:00:22,430 --> 00:00:25,440 -the patterns that you can use, you also want to study them and - -10 -00:00:25,440 --> 00:00:29,090 -study the related patterns. So normally if you look at any pattern catalog, - -11 -00:00:29,090 --> 00:00:32,229 -for each pattern there will also be a list of related patterns. So - -12 -00:00:32,229 --> 00:00:35,010 -you can also look at those to see whether maybe some of those - -13 -00:00:35,010 --> 00:00:38,370 -might be more applicable. And finally, once you identify the pattern that you - -14 -00:00:38,370 --> 00:00:41,360 -think is appropriate, you will apply that pattern. When you do that, just - -15 -00:00:41,360 --> 00:00:44,850 -be mindful that there are pitfalls in the use of patterns. One obvious - -16 -00:00:44,850 --> 00:00:47,490 -one is the fact that you might select the wrong pattern and make - -17 -00:00:47,490 --> 00:00:50,460 -your design worse instead of better. The second one is that if you - -18 -00:00:50,460 --> 00:00:52,560 -get too excited about patterns, then you - -19 -00:00:52,560 --> 00:00:54,850 -might be abusing patterns, so just using too - -20 -00:00:54,850 --> 00:00:56,370 -many patterns, and end up with a design - -21 -00:00:56,370 --> 00:00:58,980 -that is more complicated rather than less complicated. - -22 -00:00:58,980 --> 00:01:01,890 -So always be careful, spend the time to figure out which one is the right - -23 -00:01:01,890 --> 00:01:03,577 -pattern to apply, and make sure that you - -24 -00:01:03,577 --> 00:01:05,190 -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 deleted file mode 100644 index 76a78e0..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/11 - Choosing a Pattern Quiz - lang_en_vs4.srt +++ /dev/null @@ -1,31 +0,0 @@ -1 -00:00:00,160 --> 00:00:02,780 -Now that we've discussed how to choose a pattern. Imagine that - -2 -00:00:02,780 --> 00:00:05,210 -you have to write a class that can have only one - -3 -00:00:05,210 --> 00:00:08,090 -instance. So to satisfy this requirement, I would like for you - -4 -00:00:08,090 --> 00:00:10,720 -to pick one of the design patterns that we discussed in - -5 -00:00:10,720 --> 00:00:14,580 -this lesson, and write the code here that satisfies that requirement. - -6 -00:00:14,580 --> 00:00:16,270 -And when you write the code, please make sure that your - -7 -00:00:16,270 --> 00:00:21,140 -class has only one method, without counting possible constructors, and that - -8 -00:00:21,140 --> 00:00:25,120 -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 deleted file mode 100644 index c348a2c..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/12 - Choosing a Pattern Quiz Solution - lang_en_vs4.srt +++ /dev/null @@ -1,79 +0,0 @@ -1 -00:00:00,220 --> 00:00:01,750 -As we discussed in the class the right thing to - -2 -00:00:01,750 --> 00:00:05,050 -do here was to use the factory pattern. So here is - -3 -00:00:05,050 --> 00:00:07,910 -a possible code to solve the problem. Of course that there - -4 -00:00:07,910 --> 00:00:11,220 -are different possible solutions. So what we did for this code - -5 -00:00:11,220 --> 00:00:16,210 -was to first create a private, static, Singleton object called - -6 -00:00:16,210 --> 00:00:19,340 -instance, which is the one that will keep track of the - -7 -00:00:19,340 --> 00:00:22,250 -only instance that can be created on the class. Then we - -8 -00:00:22,250 --> 00:00:25,750 -define the default constructor, the constructor that doesn't take any parameter - -9 -00:00:25,750 --> 00:00:29,900 -as private. In this way other classes cannot create instances - -10 -00:00:29,900 --> 00:00:33,310 -of Singleton without calling our factory method, and finally we - -11 -00:00:33,310 --> 00:00:35,650 -create the factory method. And the factory method is very - -12 -00:00:35,650 --> 00:00:38,600 -simple. The method will first check whether an instance of - -13 -00:00:38,600 --> 00:00:40,970 -the class was already created. If it was created, it - -14 -00:00:40,970 --> 00:00:44,010 -would just return that instance. Otherwise, it will create a - -15 -00:00:44,010 --> 00:00:47,550 -new instance and assign it to that instance member variable - -16 -00:00:47,550 --> 00:00:50,960 -and then return the newly created instance. So with this code - -17 -00:00:50,960 --> 00:00:53,540 -you're guaranteed that other classes cannot bypass the factory - -18 -00:00:53,540 --> 00:00:56,530 -method, because the default constructor is private. And the that - -19 -00:00:56,530 --> 00:00:59,600 -the factory method will create one and only one instance - -20 -00:00:59,600 --> 00:01:02,020 -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 deleted file mode 100644 index 6433019..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/13 - Negative Design Patterns - lang_en_vs4.srt +++ /dev/null @@ -1,51 +0,0 @@ -1 -00:00:00,100 --> 00:00:02,210 -To conclude this lesson, I want to discuss the - -2 -00:00:02,210 --> 00:00:06,170 -concept of negative design patterns, that is, patterns that should - -3 -00:00:06,170 --> 00:00:09,600 -be avoided. Interestingly, negative patterns were also mentioned in - -4 -00:00:09,600 --> 00:00:12,950 -Christopher Alexander's book, so in the first formulation of patterns. - -5 -00:00:12,950 --> 00:00:16,219 -So negative design pattern are basically guidelines on how - -6 -00:00:16,219 --> 00:00:19,689 -not to do things. In consoles with patterns, the guidelines - -7 -00:00:19,689 --> 00:00:21,920 -on how to do things. So basically, what the negative - -8 -00:00:21,920 --> 00:00:25,170 -design patterns do is, they enable recurring design defects to - -9 -00:00:25,170 --> 00:00:28,070 -be avoided. And as we will see in this class extensively, - -10 -00:00:28,070 --> 00:00:30,080 -in mini-course four, negative patterns are - -11 -00:00:30,080 --> 00:00:33,380 -also called anti-patterns or bad smells, - -12 -00:00:33,380 --> 00:00:36,540 -or bad code smells. So in mini-course four we will see several - -13 -00:00:36,540 --> 00:00:39,480 -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 deleted file mode 100644 index 5fbb886..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/2 - History of Design Patterns - lang_en_vs6.srt +++ /dev/null @@ -1,179 +0,0 @@ -1 -00:00:00,160 --> 00:00:02,780 -Let's start our decision of design patterns by looking - -2 -00:00:02,780 --> 00:00:05,280 -at the history of patterns. As you know, I like - -3 -00:00:05,280 --> 00:00:07,810 -to give this sort of historical perspective on how and - -4 -00:00:07,810 --> 00:00:10,600 -when concepts were defined. In this case, we have to - -5 -00:00:10,600 --> 00:00:14,830 -go back to 1977, when Christopher Alexander, an American professor - -6 -00:00:14,830 --> 00:00:18,300 -of architecture at UC Berkeley, introduces the idea of patterns, - -7 -00:00:18,300 --> 00:00:21,700 -successful solutions to problems, in his book called a Pattern - -8 -00:00:21,700 --> 00:00:25,640 -Language. The book contains about 250 patterns. And the idea - -9 -00:00:25,640 --> 00:00:27,700 -is that occupants of a building should be able - -10 -00:00:27,700 --> 00:00:30,110 -to design it. And the patterns in the book provide - -11 -00:00:30,110 --> 00:00:32,368 -a way to do that. And this idea of design - -12 -00:00:32,368 --> 00:00:35,964 -patterns, so, a formal way of documenting successful solutions to - -13 -00:00:35,964 --> 00:00:41,200 -problems, inspired several other disciplines. In particular, in 1987, - -14 -00:00:41,200 --> 00:00:44,810 -Ward Cunningham and Kent Beck leveraged this idea of Alexander's - -15 -00:00:44,810 --> 00:00:48,360 -patterns in the context of an object oriented language. - -16 -00:00:48,360 --> 00:00:50,840 -And in this specific the language was Smalltalk. - -17 -00:00:50,840 --> 00:00:52,666 -Some of you might know the language. So what Cunningham - -18 -00:00:54,492 --> 00:00:56,320 -and Beck did, was to create a 5 pattern - -19 -00:00:56,320 --> 00:00:59,880 -language for guiding novice Smalltalk programmers. So they did - -20 -00:00:59,880 --> 00:01:03,090 -an experiment and had several developers using their patterns, and - -21 -00:01:03,090 --> 00:01:06,330 -the experiment was extremely successful. The users were able to - -22 -00:01:06,330 --> 00:01:09,940 -create elegant designs using the provided patterns. And in case - -23 -00:01:09,940 --> 00:01:12,210 -you are interested in reading about it, Cunningham and Beck - -24 -00:01:12,210 --> 00:01:15,660 -reported the results in the article, Using Pattern Languages for - -25 -00:01:15,660 --> 00:01:17,940 -Object Oriented Programs, which was published at the - -26 -00:01:17,940 --> 00:01:21,854 -International Conference on Object Oriented Programming, Systems, Languages, and - -27 -00:01:21,854 --> 00:01:25,390 -Applications, also called OOPSLA, in 1987. At the - -28 -00:01:25,390 --> 00:01:28,480 -same time, Eric Gamma was working on his dissertation, - -29 -00:01:28,480 --> 00:01:31,030 -whose topic was the importance of patterns and - -30 -00:01:31,030 --> 00:01:34,430 -how to capture them. Between 1987 and 1992, there - -31 -00:01:34,430 --> 00:01:37,520 -were several workshops related to design patterns. And - -32 -00:01:37,520 --> 00:01:40,740 -in 1992, Jim Coplien compiled a catalog of C++ - -33 -00:01:40,740 --> 00:01:43,140 -items, which are some sort of patterns, and - -34 -00:01:43,140 --> 00:01:45,130 -he listed this catalog of patterns in his - -35 -00:01:45,130 --> 00:01:48,720 -book, which was titled Advanced C++ Programming Styles - -36 -00:01:48,720 --> 00:01:52,952 -and Idioms. Finally, in 1993 and 1994, there were - -37 -00:01:52,952 --> 00:01:56,160 -several additional workshops focused on patterns. And this - -38 -00:01:56,160 --> 00:01:59,625 -workshop brought together many patterns folks, including these - -39 -00:01:59,625 --> 00:02:03,040 -4 guys, Erich Gamma, Richard Helm, Ralph Johnson, - -40 -00:02:03,040 --> 00:02:06,040 -and John Vlissides. These guys are also known as - -41 -00:02:06,040 --> 00:02:08,970 -the gang of 4. And the result of this collaboration was the - -42 -00:02:08,970 --> 00:02:11,840 -famous book Design Patterns: Elements of - -43 -00:02:11,840 --> 00:02:14,320 -Reusable Object Oriented Software. So this - -44 -00:02:14,320 --> 00:02:17,640 -is basically The Book on design patterns. If you want to buy - -45 -00:02:17,640 --> 00:02:19,780 -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 deleted file mode 100644 index 764a309..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/3 - Patterns Catalogue - lang_en_vs4.srt +++ /dev/null @@ -1,79 +0,0 @@ -1 -00:00:00,230 --> 00:00:03,380 -This book contains a patterns catalog which is - -2 -00:00:03,380 --> 00:00:06,725 -a number of design patterns classified by purpose. And - -3 -00:00:06,725 --> 00:00:09,122 -there are five main classes of patterns. There are - -4 -00:00:09,122 --> 00:00:11,890 -fundamental patterns which are the basic patterns. There are - -5 -00:00:11,890 --> 00:00:15,170 -creational patterns which are the patterns that support object - -6 -00:00:15,170 --> 00:00:18,290 -creation. Then there are structural patterns and these are - -7 -00:00:18,290 --> 00:00:22,090 -patterns that help compose objects, put objects together. The - -8 -00:00:22,090 --> 00:00:25,280 -next class of patterns are behavioral patterns and these - -9 -00:00:25,280 --> 00:00:28,840 -are patterns that are mostly focused on realizing interactions - -10 -00:00:28,840 --> 00:00:32,820 -among different objects. Finally, there are concurrency patterns and these - -11 -00:00:32,820 --> 00:00:36,400 -are patterns that support, as the name says, concurrency, so - -12 -00:00:36,400 --> 00:00:39,700 -they're more related to concurrency aspects. And for each of - -13 -00:00:39,700 --> 00:00:43,560 -these classes there are a number of specific patterns, and - -14 -00:00:43,560 --> 00:00:46,130 -here I'm just listing some of them. Clearly we cannot - -15 -00:00:46,130 --> 00:00:48,740 -cover in one lesson all of these patterns, but what - -16 -00:00:48,740 --> 00:00:50,440 -I want to do is to cover at least a few - -17 -00:00:50,440 --> 00:00:52,670 -of those to give an idea of what patterns are and - -18 -00:00:52,670 --> 00:00:55,430 -how they can be used. In particular, we will see in - -19 -00:00:55,430 --> 00:00:59,200 -detail the Factory Method Pattern and the Strategy Pattern. And we - -20 -00:00:59,200 --> 00:01:01,590 -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 deleted file mode 100644 index 7df86c0..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/4 - Pattern Format - lang_en_vs5.srt +++ /dev/null @@ -1,71 +0,0 @@ -1 -00:00:00,180 --> 00:00:02,711 -So let's start by seeing how patterns are defined. So - -2 -00:00:02,711 --> 00:00:05,620 -what is the format of the pattern definitions. If we look - -3 -00:00:05,620 --> 00:00:08,000 -at the Gang of Four's book we can see that these - -4 -00:00:08,000 --> 00:00:11,630 -definitions contain a lot of information. In fact, what I'm listing - -5 -00:00:11,630 --> 00:00:14,980 -here is just a subset of this information. In this lesson, - -6 -00:00:14,980 --> 00:00:17,510 -what I want to do is to focus on four essential - -7 -00:00:17,510 --> 00:00:21,480 -elements of a design pattern. It's name, the intent which is - -8 -00:00:21,480 --> 00:00:25,270 -the goal of the pattern. The pattern's applicability which is the - -9 -00:00:25,270 --> 00:00:28,040 -list of situations or context in which the - -10 -00:00:28,040 --> 00:00:31,560 -pattern is applicable. I also want to cover the structure - -11 -00:00:31,560 --> 00:00:34,700 -and participants. Which is the static model that describes - -12 -00:00:34,700 --> 00:00:37,870 -the elements, so normally the classes or the object - -13 -00:00:37,870 --> 00:00:39,900 -involved in the pattern. In addition to that - -14 -00:00:39,900 --> 00:00:41,400 -the structure also describes - -15 -00:00:41,400 --> 00:00:44,420 -the relationships, responsibilities and collaborations - -16 -00:00:44,420 --> 00:00:47,264 -among these classes or objects. Finally what I want - -17 -00:00:47,264 --> 00:00:50,560 -to cover is sample code. So examples that illustrate - -18 -00:00:50,560 --> 00:00:51,490 -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 deleted file mode 100644 index c7ebddd..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/5 - Factory Method Pattern - lang_en_vs5.srt +++ /dev/null @@ -1,179 +0,0 @@ -1 -00:00:00,012 --> 00:00:02,350 -Let's now look at the first design pattern that we - -2 -00:00:02,350 --> 00:00:05,700 -will discuss, the factory method pattern. And I'm going to start - -3 -00:00:05,700 --> 00:00:09,220 -by discussing the intent of the pattern and its applicability. - -4 -00:00:09,220 --> 00:00:12,210 -As far as the intent is concerned, the factory method pattern - -5 -00:00:12,210 --> 00:00:16,690 -allows for creating objects without specifying their class, by invoking - -6 -00:00:16,690 --> 00:00:19,370 -what we call a factory method. And what that is, is - -7 -00:00:19,370 --> 00:00:22,680 -a method whose main goal is to create class instances. - -8 -00:00:22,680 --> 00:00:25,510 -So when is this pattern useful? So when is it applicable? - -9 -00:00:25,510 --> 00:00:28,080 -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 deleted file mode 100644 index 2812c39..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/6 - Factory Method Pattern Example - lang_en_vs5.srt +++ /dev/null @@ -1,127 +0,0 @@ -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 deleted file mode 100644 index 288b8d6..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/7 - Strategy Pattern - lang_en_vs5.srt +++ /dev/null @@ -1,143 +0,0 @@ -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 deleted file mode 100644 index 6d298d0..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/8 - Strategy Pattern Example & Demo - lang_en_vs5.srt +++ /dev/null @@ -1,511 +0,0 @@ -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 deleted file mode 100644 index 756f38f..0000000 --- a/usth/ICT2.7/P3L3 Design Patterns Subtitles/9 - Other Common Patterns - lang_en_vs5.srt +++ /dev/null @@ -1,295 +0,0 @@ -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. |